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ADME 1

Lecture Overview

• Importance of keeping up with lectures for final assessment preparation

  • Encouragement to attend lectures regularly to stay on track

• Emphasis on understanding and mastering foundational concepts before moving on to more complex topics

  • Mention of absorption topic requiring basic math skills

  • Assuring that the math involved is not difficult, just about rearranging equations

• Mention of Liam's ability to help students struggling with math

  • Contrasting teaching approaches between the speaker and Liam

• Call for nominees for the Staff Student Consultative Committee

  • Importance of having representation for student feedback discussions

  • Mention of Rachel and Jackie's roles in keeping student feedback in check

Staff Student Consultative Committee Nominees

• Need for nominees for the committee

  • Mention of Jackie asking for two nominees

• Importance of having at least one person representing the course

  • Benefits for CV and taking student feedback seriously

• Suggestion to have more representation for morning and afternoon streams

• Acknowledgment of Rachel and Jackie's roles in managing student feedback.

Main Ideas from the Transcript

Emphasis on Passive Diffusion

• Historical focus on passive diffusion in biological processes.

• Heavy emphasis on physical chemical characteristics driving passive processes.

• Medieval chemists believed changing lipophilic properties would enhance absorption and metabolism.

• Ignored biological processes in favor of chemical characteristics.

Importance of Transport in Pharmacology

• Transport is a crucial but understudied area in pharmacology.

• Absorption, distribution, metabolism, and excretion (ADME) are interdependent processes.

• Absorption is the initial step and a prerequisite for other processes.

• Failure in drug development often stems from inadequate understanding of pharmacokinetics in humans.

Membrane Crossing and Diffusion

• Membranes are lipophilic and polar, affecting drug absorption.

• Passive diffusion is driven by concentration gradients without requiring energy.

• Diffusion can be transcellular (through cells) or paracellular (around cells).

• Paracellular diffusion involves water-soluble substances passing through aqueous pockets.

• Tissue-dependent differences impact the rate of diffusion in various tissues.

Challenges in Drug Development

• The mantra of drug lipophilicity for absorption and hydrophilicity for excretion.

• Understanding the complexities of membrane crossing and diffusion pathways.

• Tissue-specific variations in passive diffusion rates.

By understanding the historical context of passive diffusion, the importance of transport mechanisms in pharmacology, and the complexities of membrane crossing and diffusion pathways, researchers can address challenges in drug development and optimize drug absorption and distribution in different tissues.

Blood Brain Barrier and Tissue Accumulation

• Blood Brain Barrier

  • Acts as a selective barrier for compounds

  • Cells in the brain have tight boundaries, limiting passage

• Liver and Spleen

  • Contrasted with the brain in terms of permeability

  • Liver cells have leakier boundaries allowing for easier transport

Factors Affecting Diffusion

• Passive Diffusion

  • Moves down concentration gradient

  • Influenced by surface area, membrane thickness, and molecule permeability

• Rate of Diffusion Calculation

  • Involves concentration gradient, surface area, and permeability factor

  • Determines the speed of diffusion across membranes

Lipophilicity and Partitioning

• Log P

  • Measure of lipid solubility

  • Determines if a compound favors cellular or transcellular transport

• High-Log P vs. Low-Log P

  • High log P favors lipophilic membrane crossing

  • Low log P favors paracellular transport

Examples of Compounds

• Flow to Pain

  • Lipophilic antihypertensive drug

• Ibuprofen

  • Relatively flat log P, water-soluble

• Organic Solvents in Chemical Synthesis

  • Considerations for pH regulation in tissues

• pKa and Ionization

  • Important for pharmacologists in predicting drug behavior based on tissue pH

pH and Drug Distribution

• Buffered pH

  • Tissues buffered tightly to specific pH levels

  • pH regulation critical for metabolic functions and survival

• Log P and Ionization

  • Log P values change with ionization state

• pH-Dependent Drug Distribution

  • Investigated using log P values in different pH buffers

• Upcoming Workshops

  • Further exploration of drug distribution based on tissue pH in the lab next week

Acid-Base Chemistry and Ionization

• Acid proton donor becomes negatively charged

  • Proton acceptor becomes positively charged

• Charged molecules move into acidic environments based on charge

• Ionization affects movement through membranes

  • Non-ionized forms pass through lipophilic membranes

• Henderson-Hasselbeck equation used to calculate concentration gradients

  • Equilibrium between weak acids and their ions

  • pH and pKa relationship for easier handling of numbers

• Principles of rearranging equations and logarithms

  • Logarithms simplify multiplication to addition

  • Rearranging equations to calculate ionized and non-ionized forms

Drug Absorption and Elimination

• Different pKa values for molecules affect ionization

  • Compounds with multiple pKa values

• Weak acids like penicillin-based antibiotics and aspirin

• Bases also have pKa values

  • More basic compounds more likely to pick up a proton

• Influence of pKa on drug excretion and elimination

  • Changing urine pH to alter excretion of compounds

• Impact of pH on drug absorption in the stomach

  • Weak bases and acids' absorption based on ionization

Practical Applications in Drug Testing

• Changing elimination of compounds through ion trapping

• Calculations using Henderson-Hasselbeck equation for blood and urine

• Influence of tissues on drug distribution and elimination

• Maceration in the stomach aiding drug absorption

• Prediction of drug absorption based on acid-base properties

Breast Milk and Drug Distribution

• Breast milk has a different pH, affecting drug transfer to infants

  • Concerns about exposing infants to drugs through breastfeeding

  • Calculations using Henderson-Hasselbalch equation to determine drug concentrations

• Weak acids are less concentrated in breast milk compared to more acidic substances

• Changes in drug molecules impact absorption, distribution, and elimination

• Lipophilic drugs tend to accumulate in fat tissues, requiring higher doses for efficacy

Protein Binding and Distribution

• Protein binding impacts drug concentration and distribution

  • pH influences ionic interactions affecting protein binding

• Free drug concentration is crucial for pharmacokinetics

• Irreversible binding can lead to toxicity

• Passive diffusion, lipophilicity, and ionization play roles in drug distribution

Transporters in Pharmacology

• Transporters in pharmacology require energy and can move drugs against concentration gradients

• Active transport is faster but energy-intensive compared to passive diffusion

• Various transporters like uniporters, symporters, aquaporins, ion channels, and ABC transporters play roles in drug transport

• ABC transporters like organic acid transporter, organic anion-transporting polypeptide, and cation transporter are crucial for drug movement based on ionization and charge

Key Takeaways

• Understanding drug distribution in breast milk is essential for infant safety

• Protein binding and distribution impact drug efficacy and toxicity

• Transporters play a vital role in active drug transport across membranes

• Ionization and charge influence drug uptake by specific transporters in pharmacology

Main Ideas from the Transcript

ABC Transporters

• ABC transporters are important in pharmacokinetics and pharmacodynamics.

  • Tumor cells overexpress some transporters, leading to drug resistance.

  • They are named based on substrates and have a systematic nomenclature.

  • Examples include MDR one (multidrug resistant one) and P-glycoprotein.

Importance of Blood-Brain Barrier

• Blood-brain barrier is crucial for drug effects on the central nervous system.

  • Prevents drugs from entering the brain, avoiding neurological effects.

  • Compromising the barrier can lead to unexpected drug effects.

  • Brain tumors are challenging to treat due to the barrier's protection.

Drug Safety and Transporters

• P-glycoprotein plays a key role in drug safety by preventing substances from crossing the blood-brain barrier.

  • Inhibiting P-glycoprotein can alter drug distribution and lead to unexpected effects.

  • Transporters are present on various cell membranes and play a role in excretion.

Pharmacokinetics and Absorption

• Understanding absorption processes is essential for drug effectiveness.

  • Consider passive and active absorption, ionization, and lipid-ion

ADME 2

Drug Metabolism Overview

• Metabolism Impact:

  • Metabolism affects how drugs interact with biological systems and their pharmacological activity.

  • Important in drug development and med chem for tweaking molecules.

Terminology and Concepts

• Detoxification:

  • Metabolism can lead to detoxification, making drugs safer by eliminating them.

  • All drugs are considered poisons, and detoxification helps in reducing toxicity.

• Bioactivation:

  • Some drugs can be metabolized into toxic compounds, like paracetamol leading to liver toxicity.

  • Bioactivation can also convert pro-drugs into active forms for pharmacological activity.

• Detox:

  • In some cases, metabolism can convert toxic compounds into safer forms.

  • Example with paracetamol where detoxification systems help in preventing liver damage.

Metabolism and Drug Activity

• Metabolism Overview

  • Metabolism can be both beneficial and harmful.

  • The goal is to change the chemical properties of a substance to make it more water-soluble for elimination.

  • Lipophilic substances need to be made hydrophilic for excretion through urine to avoid kidney damage.

• Drug Metabolism Impact

  • Drug metabolism aims to make compounds more polar and water-soluble.

  • Altering the chemical structure of a molecule can affect its interaction with biological targets.

  • Changes in chemical structure may not always impact pharmacological activity significantly.

• Examples of Metabolism Impact

  • Diazepam metabolism to nordiazepam shows no significant change in pharmacological activity.

  • Pro-drugs are designed to be metabolized into active agents for better absorption.

  • Codeine metabolizes into morphine and glucuronide, with the latter having better activity.

  • Aspirin's active compound is salicylic acid, which is less harsh on the stomach.

  • Tamoxifen's metabolite showed more activity than the original drug, leading to better pharmacology.

• Importance in Drug Development

  • Understanding metabolism is crucial for effective drug development.

  • Preclinical studies need to focus on the correct active compounds to ensure efficacy in humans.

Organ Specific Metabolism

• Liver as the Primary Organ

  • The liver is the main organ for drug metabolism due to its abundance of enzymes.

  • Oral drugs are first metabolized in the liver after absorption.

  • Other organs like the lungs can also metabolize drugs, impacting their effectiveness.

• Organ-Specific Enzyme Variability

  • Different organs have varying enzyme profiles, leading to organ-specific metabolism.

  • While the liver and kidneys have similar enzymes, there are differences in their metabolic activities.

Enzyme Reactions and Metabolism

• Enzyme Reactions

  • Broad categories: oxidation reduction, hydrolysis (phase one reactions)

  • Focus on oxidation due to the quantitative importance in drug metabolism

  • Today's focus: conjugation reactions to provide the other side of the story

• Cytochrome P450 (CYP) Families

  • Major families in drug metabolism: CYP1, CYP2, CYP3

  • Specific physiological roles for other CYP families (e.g., retinoic acid metabolism)

  • Importance of understanding CYP families in drug development and safety

• CYP Subfamilies and Isoforms

  • CYP proteins with a maximum spectrum at 459 nm

  • Subfamilies within major families (e.g., CYP2A, CYP2B, CYP2C, CYP2D, CYP2E)

  • Discovery order dictates numbering (e.g., CYP2C19, CYP2D6, CYP2C8 in humans)

Conjugation Reactions and Drug Metabolism

• Conjugation Reactions

  • Anabolic reactions making molecules larger and more polar

  • Involves attaching water-soluble endogenous molecules to drugs

  • Changes in molecular weight and polarity affect pharmacodynamic activity

• Phase Metabolism

  • Phase 1: Oxidation by cytochrome P450 enzymes

  • Phase 2: Conjugation reactions to add molecules like glucose or amino acids

  • Phase 3: Transporters move metabolites out of cells for excretion

• Preference in Metabolism

  • Body's preference for phase 3 over phase 2 and phase 1

  • Introduction of functional groups when phase 2 or 3 pathways are not feasible

• Importance of Conjugation Reactions

  • Quantitatively the most important pathway in drug metabolism

  • Essential for metabolizing both endogenous substances and drugs

Conclusion

Understanding enzyme reactions, CYP families, and conjugation reactions is crucial in comprehending drug metabolism and ensuring drug efficacy and safety in pharmaceutical development.

Main Ideas from the Transcript

Drug Metabolism Mechanisms

• Endogenous substrates undergo quick transition during metabolism.

  • Steroids, catecholamines, bilirubin are massively indebted to their excretion.

• Old drugs (40-70%) undergo glucuronidation for elimination.

• New drugs do not necessarily undergo glucuronidation due to alternative elimination mechanisms like Sips superfamily enzymes.

Glucuronidation Process

• Glucose acid molecule (molecular weight 877) is added to drugs to increase water solubility.

• Glucose acid makes drugs more water-soluble and terminates their activity.

• Glucuronidation involves phase one (P450 introducing hydroxyl group) and phase two (glucose acid conjugation) actions.

• Exceptions like morphine and codeine show parallel or series phase one and phase two actions.

Enzyme Specificity and Location

• Different enzymes in different locations have broad substrate selectivity.

• Enzyme importance depends on exposure route (oral vs. inhalation).

• Enzymes like 1A1 in the liver metabolize endogenous substrates and drugs.

• Enzymes like 1A3 in the GI tract are important based on route of drug administration.

Glutathione Transferase

• Glutathione transferase catalyzes reactions with glutathione to detoxify drugs.

• Different families of glutathione transferase have broad substrate selectivity.

• Glutathione transferase is not quantitatively important in drug metabolism to avoid toxicity.

Tissue-Specific Metabolism

• Different tissues have varying profiles of enzymes like glutathione transferase.

• Liver, kidney, and lung produce different metabolites impacting drug safety and effectiveness.

Acetylation and Drug Metabolism

• Acetylation was the first drug-metabolizing enzyme where polymorphisms were identified.

  • Started with an alcohol transferase enzyme.

  • Patients with adverse reactions lacked sufficient enzyme activity.

• Acetylation makes compounds less polar by masking hydroxyl groups.

  • Helps in designing drugs like aspirin for better bioavailability.

• Drug metabolism involves two major families of enzymes: polymorphic and highly inducible.

  • Expression levels depend on the substrate taken.

• New drugs are often substrates for drug-metabolizing enzymes due to polymorphisms.

• Methylation, like acetylation, reduces polarity of compounds.

  • Methylation can affect solubility and drug activity.

• Amino acid conjugation involves adding an amino acid to a compound.

  • Common in mitochondria for drug metabolism.

Complexities in Drug Metabolism

• Drug metabolism pathways can be messy and involve multiple metabolites.

• Metabolites can have different pharmacological activities than the parent compound.

• Drug metabolism is not a linear process but can involve parallel or sequential pathways.

• Transporters play a role in eliminating metabolites from the body.

  • Transporters recognize polar compounds and aid in excretion.

• Transporters can dictate whether metabolites are excreted in bile or urine.

• Drug metabolism is not as simple as just passing through membranes due to directional cells.

Conclusion

• Drug metabolism is a complex process involving various enzymes and pathways.

• Understanding drug metabolism is crucial for drug design and efficacy.

• The interplay between enzymes, polymorphisms, and transporters influences drug metabolism outcomes.

Importance of Drug Metabolism

• Variability in Drug Metabolism

  • Genetic and induction factors contribute to variability.

  • Body responds to chemical stress through induction.

• Impact of Enzyme Expression

  • Enzyme induction is a slow process, taking a couple of days.

  • Daily medication intake leads to changes in metabolic clearance over time.

• Influence of External Factors

  • Smoking, diet, and other lifestyle choices can affect enzyme expression.

  • Changes in enzyme expression complicate investigations and contribute to variability.

Drug-Drug Interactions and Genetic Variability

• Enzyme Inhibition

  • Inhibition of metabolic elimination can lead to increased drug concentration.

  • Rapid effects can occur without changes in protein expression.

• Genetic Polymorphisms

  • Drug companies screen out polymorphisms to ensure broader drug effectiveness.

  • Older drugs may be more susceptible to genetic variability issues.

Patient Factors and Drug Metabolism

• Factors Affecting Metabolism

  • Age, pregnancy, diet, and other medications impact drug metabolism.

  • Understanding individual metabolic capacity is crucial for drug efficacy and safety.

• Career Opportunities

  • Pharmaceutical companies heavily invest in drug metabolism research.

  • Drug metabolism knowledge is essential for drug development and safety assessments.

Pharmacokinetics and Predicting Interactions

• Importance of Pharmacokinetics

  • Understanding dose-concentration-effect relationships over time is crucial.

  • Predicting and preventing drug-drug interactions is vital for patient safety.

• Genetic Influence on Metabolism

  • Lack of metabolism pathways can lead to unexpected drug concentrations.

  • Genetic variations can impact drug efficacy and toxicity levels.

Conclusion

• Predicting Drug Interactions

  • Enhanced understanding of drug metabolism aids in predicting and preventing adverse interactions.

• Future Discussions

  • Further lectures and lab sessions will delve into reaction phenotyping and genetic influences on drug metabolism.

Main Ideas from the Transcript

Eyes as Reducing Toxicity

• Eyes can be used to reduce toxicity through drug interactions.

• Drug interactions can prevent people from experiencing toxicity.

• Examples of using drug interactions to prevent toxicity are rare.

Species Differences in Metabolites

• Species like mice, rats, rabbits, and humans metabolize drugs differently.

• Enzyme cytochrome P450 varies slightly in amino acid sequence between species.

• Variations in enzyme sequences lead to differences in substrate selectivity among species.

ADME 3

Chapter 1: Introduction

• Adeyemi's importance in pharmacokinetics emphasized by Jackie.

  • Processes to focus on: absorption, distribution, metabolism, excretion.

• Henderson Hasselbeck equation discussed in detail.

  • Precision and accuracy in understanding demonstrated by students.

• Routes of drug excretion explained.

  • Factors influencing renal function highlighted.

  • Drug journey from absorption to excretion through liver and kidneys described.

• Importance of understanding drug elimination pathways stressed.

  • Different factors affecting excretion into bile or urine mentioned.

  • Molecular weight cut-off for excretion discussed, with variations between species.

• Significance of biliary excretion and transporters in drug elimination emphasized.

  • Polarization of cell membranes and transport mechanisms explained.

Chapter 2: Process Of Concentration

• Inhalation anaesthetics are older drugs that are designed to be pharmacologically active but chemically inactive.

  • Metabolism of inhalation anaesthetics can lead to toxicities.

  • They are eliminated through exhalation, making it easy for anaesthetists to adjust dosage.

• Sweat can also be a route of elimination for certain drugs like amphetamines, cocaine, and cannabinoids.

  • Some drugs can be detected in sweat, providing information on substances taken.

• Kidney function involves pressure filtration in the glomerulus and concentration processes in the tubules.

  • Water and substances are reabsorbed to maintain body hydration and balance.

  • Presence of blood or protein in urine can indicate kidney damage.

Chapter 3: Active Active Secretion

• Drug excretion through the kidney involves physical processes like glomerular filtration rate and active tubular secretion.

  • Different transporters in the proximal and distal tubules handle substances like Penicillins based on charge.

• Changes in urinary pH can affect drug equilibrium and secretion.

• Transporters in cells play a crucial role in absorption and secretion processes.

  • Transporters in the kidney help in reabsorption or active secretion of substances.

  • Similar transporters are involved in processes like blood-brain barrier regulation.

Chapter 4: Know Increasing Urine

• Passive Reabsorption in the Loop of Henle

  • Loop length varies based on water conservation needs

  • Cats have long loops for water salvage, leading to concentrated urine

• Factors Affecting Renal Drug Excretion

  • GFR and urine flow rate impact drug excretion

  • Ionization of weak acids affects passive reabsorption

• Active Processes and Transporters

  • Inhibition of active transporters can alter drug absorption, distribution, and excretion

• Influence of Urine Flow on Drug Concentration

  • Increased urine flow decreases drug concentration

  • Passive process driven by mass action law

Chapter 5: Know The Structure

• Glomerular Filtration Rate (GFR)

  • Total volume of filtrate produced by the Nephron

  • Changes in blood flow affect GFR, about 10% of blood volume filtered

• Significance of GFR in Health

  • GFR decreases with age, impacting drug elimination and dosing

  • GFR is a marker of kidney function without invasive procedures

• Measurement of GFR

  • Ideal compounds for GFR measurement undergo only passive filtration

  • Inulin is a gold standard compound for GFR measurement

Chapter 6: Steady State Concentration

• Creatinine as an Indicator

  • Creatinine is used to estimate renal function.

  • Creatinine levels vary based on sex and muscle mass.

  • Steady state concentration of creatinine in the body is maintained.

  • Kidneys play a crucial role in maintaining steady state concentration.

• Drug Elimination and GFR

  • Drug elimination depends on glomerular filtration rate (GFR).

  • Higher GFR leads to faster drug elimination through urine.

  • Adjusting drug doses based on individual GFR levels ensures safe and effective drug concentration.

  • Useful for drugs with narrow therapeutic windows.

• Dosing Adjustment

  • Dose adjustment based on GFR helps achieve desired drug concentration.

  • Different individuals may require different doses to reach the same safe concentration.

  • Important for drugs with narrow therapeutic windows to prevent adverse effects.

• Ionized Concentration Calculation

  • Adjusting ionized concentration helps determine drug flow across membranes.

  • Understanding ionized concentration gradients guides drug elimination pathways.

  • Important in scenarios like aspirin overdose for effective treatment.

• Aspirin Overdose

  • In aspirin overdose, understanding ionized concentration gradients is crucial.

  • Higher ionized concentration in urine facilitates drug elimination.

  • Monitoring peak drug levels and ionized concentrations aids in treatment planning.

Chapter 7: Drug Elimination and Pharmacokinetics

• Weak acids like herbicides can be toxic if ingested mistakenly

  • Alkalizing urine can aid in eliminating the toxin before harm

• Weak bases like methamphetamine can be manipulated for drug tests

  • Pharmacological knowledge can help in altering drug concentrations for desired effects

• Drug elimination involves active transport into bile and excretion into the gut

  • Reabsorption from the gut can lead to prolonged drug effects and altered pharmacokinetics

Chapter 8: Drug Disposition in the Body

• Drug absorption and distribution are crucial for pharmacological effects

  • Protein binding and tissue distribution impact drug availability and efficacy

• Fat distribution in the body affects drug partitioning and availability

  • Different body compositions can influence drug effects and intensity

Chapter 9: Competing Processes in Drug Metabolism

• Drug metabolism and excretion occur simultaneously with drug effects

  • Intrahepatic recirculation through bile can impact drug concentrations and efficacy

Conclusion

• Emphasizes the complexity of drug elimination and metabolism

• Highlights the importance

PK1

Introduction

• Pharmacokinetics is an important area related to medicines

• It is essential for understanding how drugs work in the body

• The focus is on dose to concentration relationship

Importance of Pharmacokinetics

• Pharmacokinetics is crucial for achieving therapeutic effects of medicines

• Understanding drug absorption, distribution, metabolism, and excretion is key

• Factors like dose, route, duration, and tissue targeting are considered

• Safety, toxicity, and pharmacodynamics are also important aspects

Pharmacokinetic Processes

• ADME (Absorption, Distribution, Metabolism, Excretion) are key processes

• Absorption involves factors like tissue characteristics, ionization, and drug size

• Distribution refers to where the drug travels in the body and its reversibility

• Elimination involves excretion and metabolism of the drug

• Various factors like tissue binding, transporters, and body size influence drug distribution

• Genetic differences and lifestyle factors can impact pharmacokinetic processes

Conclusion

• Pharmacokinetics plays a vital role in ensuring drugs reach the right place at the right time in the body

• Understanding ADME processes is essential for effective drug therapy

• Factors like absorption, distribution, and elimination are complex and influenced by various physiological and external factors

Pharmacokinetics Simplified

Drug Absorption and Distribution

• Drug process overlaps as soon as it enters systemic circulation

  • Distribution and elimination occur simultaneously

• Pharmacokinetics simplifies complex processes

  • Focuses on input, distribution, and elimination

• Absorption may not occur in some cases

  • Example: I.V. bolus directly injected into circulation

• Pharmacokinetic models focus on how drugs enter the system

Importance of Pharmacokinetics

• Integrates data to make informed decisions

• Quantitative description of drug concentration over time in the body

• Emphasizes measuring plasma concentrations for dose-effect relationship

Concentration and Drug Effect

• Plasma concentration crucial for drug effect

• Circulation delivers drug to target organs and sites of action

• Steady state reached with consistent concentration throughout the body

• Plasma concentration serves as a proxy for receptor concentration

Significance of Plasma Concentration

• Acts as a bridge between dose and effect

• Allows understanding of dose-concentration-effect relationships

• Facilitates targeting desired drug concentrations for specific effects

Therapeutic Range and Pharmacodynamic Curves

• Definition of Therapeutic Range

  • Range of drug concentration in the body that produces the desired effect without causing significant adverse effects.

• Pharmacodynamic Curves

  • Two curves shown: one for the desired effect and the other for adverse effects.

  • Example of Propofol, a hypnotic drug used as an anesthetic.

    • Effect curve could represent going to sleep, while adverse effects curve could represent hemodynamic instability.

• Relationship Between Concentration and Effects

  • As drug concentration increases, adverse effects may emerge.

  • Overlapping of the curves determines ease of using the medicine.

    • Closer overlap means less separation between effective and harmful concentrations.

• Example with Paracetamol

  • Taking two 500mg tablets for a headache is common and safe.

  • Taking a whole packet can lead to problems due to overdose risk.

  • Despite safety, overdoses of paracetamol are common.

• Population and Drug Safety

  • Most of the population takes similar drugs.

  • Discussion on the width of the curves for drug safety assessment.

    • Participants agree that the curves shown are quite close together, indicating a narrow therapeutic range.

• Therapeutic Range and Achieving Therapy

  • The therapeutic range aims to achieve therapy at the upper ranges of the curve for the desired effect.

Main Ideas

Determining Therapeutic Index

• Defining narrow therapeutic rang

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  • Challenging to eyeball, so a number is assigned.

  • Examples of drugs with narrow ranges: antiepileptic drugs, antibiotics like Gentamicin, antiarrhythmics, lithium.

• Understanding curve steepness

  • Not all parts of the curve are equally steep.

  • Changes in concentration can have varying effects based on curve steepness.

• Using target concentration for dosing decisions

  • Selecting a target concentration within the therapeutic range.

  • Using models and equations to determine appropriate doses based on patient factors.

Pharmacodynamic Plot Analysis

• Non-linear relationship between response and plasma concentration

  • Curve shape is sigmoidal, not linear.

  • Changes in concentration have different effects based on curve steepness.

• Impact on dosing decisions

  • Concentrations closer to edges of the therapeutic range can lead to significant changes in effects.

  • Importance of selecting appropriate target concentration for dosing decisions.

Rational Drug Administration

• Selecting target concentration

  • Common sense approach to choosing a concentration within the therapeutic range.

  • Using models and equations to calculate doses based on patient-specific factors.

• Role of pharmacokinetics

  • Essential for determining appropriate drug doses based on therapeutic index and patient characteristics.

Understanding Rational Dosing in Pharmacokinetics

Factors to Consider for Rational Dosing

• Distribution into the body

  • Drug distribution into plasma or other tissues affects dosing.

• Rate of elimination

  • Matching elimination rate with input rate is crucial for maintaining target concentration.

Parameters in Pharmacokinetics

• Definition

  • Parameters are constants describing the system, e.g., volume distribution, clearance.

• Estimation

  • Parameters are estimated from data due to variability in individuals.

• Importance of Variability

  • Understanding variability helps in adjusting drug doses based on individual differences.

Volume Distribution

• Equation: Concentration = Dose/Volume

• Significance

  • Volume distribution explains the relationship between dose and measured concentration.

• Examples

  • Different concentrations indicate varying volume distributions based on drug characteristics.

Importance of Volume Distribution in Dosing

• Equation for Dosing

  • Concentration = (Loading Dose)/Volume helps in dosing to achieve target concentration.

• Apparent Volume

  • Volume distribution is theoretical but correlates with drug characteristics for dosing accuracy.

Standardization of Volumes

• Standardized to 70 kilograms for adult body size

  • Used in physiology literature for comparison

• Volume of distribution estimates vary for different drugs

  • Larger body size results in a bigger volume distribution

• Examples of volume distribution estimates

  • Plasma: 3 liters for a 70 kg adult

  • Heparin: stuck in plasma due to being a macro molecule

  • Warfarin: about 98% bound to plasma proteins

  • Antibiotics: similar volume distribution to extracellular fluid

  • Total body water: about 40 liters for a 70 kg adult

  • Digoxin: binds tightly to tissue proteins, leading to a theoretical value

Factors Affecting Volume Distribution

• Ethanol, alcohol, and caffeine have similar volume distribution to body water

• Digoxin binds to albumin and other plasma proteins

• Lean body mass influences volume distribution

  • Reduction in lean body mass in elderly affects distribution

• Loading doses adjustment needed for neonates due to rapid changes in body water

Different Terms and Estimation Methods

• Different terms like V, Vd, V1, V2 used in compartment models

• Different ways to estimate volumes in literature

• Volume steady state ratio differs from compartment volumes estimation

• Non-compartmental analysis for basic estimation of parameters

• Early concentration measurement for volume of distribution estimation

• Nonlinear regression for precise parameter estimation using complex software

Conclusion

• Nonlinear regression is essential for precise parameter estimation in pharmacokinetics

• Computers used for complex calculations instead of manual methods

Key Points from the Transcript:

• Scaling with Body Size

  • Bigger body = bigger volume distribution; smaller body = smaller volume distribution.

  • Need to consider scaling for both preclinical and clinical scenarios.

  • Challenge: Scaling doses from adults to neonates or from one species to another.

• Matrix Scaling

  • Based on extensive data from various species over many years.

  • Volumes typically scale linearly with weight.

  • Formula: Population volume * individual weight / population weight = estimated individual volume.

• Physiologically Based Approaches

  • More complex methods for scaling doses.

  • Utilize different approaches to transition between preclinical species and human trials.

• Software Models

  • Commercially available software based on years of data.

  • Helps in predicting dose scaling for different scenarios.

PK 3

Introduction

• Pharmacokinetics may seem dry but is crucial for safe and effective medicine use.

• Understanding clearance, volume, absorption, and elimination is essential for dosing.

Clearance and Renal Component

• Clearance is a proportionality constant describing drug elimination rate and body concentration.

• Renal clearance involves glomerular filtration, active secretion, and passive reabsorption.

  • Glomerular filtration filters unbound small molecules.

  • Active secretion pumps substances across, creating concentration gradients.

  • Passive reabsorption reabsorbs filtered substances due to concentration gradients.

• Renal clearance can be tied back to drug knowledge from pharmacokinetics.

• Example with metformin shows how interactions like with cimetidine can affect clearance and exposure.

Hepatic Clearance

• Liver plays a significant role in drug metabolism for elimination.

• Most drug metabolism occurs in the liver, contributing to overall elimination processes.

• Some drugs undergo metabolism in the kidney, but liver metabolism is predominant.

Conclusion

• Understanding renal and hepatic clearance is vital for predicting drug interactions and dosing adjustments.

• Pharmacokinetics forms the foundation for safe and effective medication use.

Enzymes and Cofactors

• Enzymes require cofactors to function effectively.

  • Enzymes and cofactors are present in high concentrations in the body for specific purposes.

  • Cofactors help in metabolizing medicines.

• Enzymes and cofactors form complexes to metabolize drugs.

  • Enzymes are taken up in the complex and release metabolites.

  • Sometimes enzymes dissociate to act on other drug molecules.

First-Order Kinetics

• In first-order kinetics, there is a proportional relationship between concentration and rate of elimination.

  • Concentration increase leads to a proportional increase in the rate of elimination.

  • Doubling the dose doubles the concentration, following a proportional relationship.

Zero-Order Kinetics

• Zero-order kinetics occurs when the rate of elimination becomes independent of concentration.

  • The system operates at its maximum capacity.

  • The rate of elimination curve appears flat on a concentration versus rate graph.

Nonlinear Kinetics

• Nonlinear kinetics occur when drugs operate in the upper part of the curve.

  • V max (maximum velocity) and K M (Michaelis constant) describe the curve's shape.

  • The elimination rate equation involves V max, K M, and concentration.

• Drugs displaying nonlinear kinetics may have restrictions on clearance pathways.

  • Enzymes and transporters are often involved in nonlinear kinetics.

  • Clearance is a constant proportional to concentration in first-order kinetics.

Example: Phenytoin

• Phenytoin is an example of a drug with nonlinear kinetics.

  • It has a narrow therapeutic range.

  • Concentrations outside the therapeutic range can lead to severe side effects.

• Phenytoin's pharmacokinetics are affected by genetic variability in metabolizing enzymes.

  • Genetic variations can impact the metabolism of phenytoin, making its use challenging for some patients.

Linear vs Non-linear Kinetics

• Linear Kinetics

  • Relationship between dose and concentration: Proportional relationship in linear kinetics.

  • Half-life: Independent of concentration, takes 4 to 5 half-lives for drug elimination.

• Non-linear Kinetics

  • Dose and concentration relationship: Not proportional in non-linear kinetics.

  • Half-life: Not applicable in non-linear kinetics, elimination time varies.

  • Impact of concentration: High concentrations lead to longer drug presence in the body.

Phenytoin Example

• Dose Influence on Concentration

  • Linear Kinetics: Predictable relationship between dose and concentration.

  • Non-linear Kinetics: Small dose changes result in significant concentration variations.

  • Therapeutic Range: 10 to 20 units, critical for dosing accuracy.

Ethanol Metabolism

• Ethanol Clearance

  • Metabolism: Involves multiple pathways for clearance.

  • Clearance Rate: Maximum velocity for ethanol elimination.

  • Comedic Example: Study on ethanol infusions showing accumulation and redistribution phases.

Conclusion

• Assessment in Drug Development

  • Proportional vs Non-linear Kinetics: Essential for determining dosing strategies.

• Real-life Example: Ethanol

  • Metabolism Complexity: Various pathways for ethanol clearance.

• Study Example

  • Ethanol Infusion Study: Demonstrating accumulation and redistribution phases in drug concentration.

Main Ideas

Ethanol Kinetics

• Ethanol elimination involves redistribution, zero-order kinetic profile, and first-order kinetic profile.

  • Redistribution occurs rapidly due to ethanol being a small molecule.

  • Zero-order kinetic profile represents constant metabolization rate.

  • First-order kinetic profile reemerges after saturation.

• Rate of elimination is determined by clearance and concentration for non-saturated components.

  • Renal clearance and hepatic clearance contribute to the elimination process.

  • Hepatic clearance is described by Michaelis-Menten equation.

Nonlinearity in Kinetics

• Nonlinearity can be observed in processes like clearance and metabolism.

• Example of nonlinearity in EPO kinetics due to complex receptor-mediated kinetics.

  • EPO dose versus area under the curve relationship is nonlinear.

  • Nonlinearity not due to metabolism but receptor binding and degradation.

• Two-compartment model used to describe EPO kinetics.

  • Includes distribution compartment and receptor-mediated elimination pathway.

Absorption and Bioavailability

• Absorption process involves extent and rate components.

• Extent refers to how much drug is absorbed, while rate is how fast absorption occurs.

• Bioavailability represents the fraction of the dose reaching circulation intact.

• Incomplete absorption may occur due to various factors like metabolism and loss in different organs.

• Extraction ratio in the liver indicates efficiency in drug elimination.

• Issues with bioavailability can lead to drugs dropping out of development pipelines.

Note

In the discussion, the speaker explains the kinetics of ethanol elimination, highlighting redistribution, zero-order, and first-order kinetic profiles. The rate of elimination is determined by clearance and concentration for non-saturated components. Nonlinearity in kinetics is exemplified through EPO kinetics, where receptor-mediated kinetics lead to a nonlinear relationship between EPO dose and area under the curve. A two-compartment model is used to describe EPO kinetics, incorporating a distribution compartment and a receptor-mediated elimination pathway. The speaker also touches on absorption and bioavailability, emphasizing the importance of understanding the extent and rate of absorption, as well as factors affecting bioavailability like metabolism and organ-specific drug loss. Extraction ratio in the liver is discussed as a measure of drug elimination efficiency, with issues in bioavailability being a significant challenge in drug development.

Main Ideas

Bioavailability

• Small changes in drug formulation can lead to changes in bioavailability.

  • Concentrations can go out of the therapeutic range.

• Bioavailability affects the height of the peak concentration.

  • More drug leads to a higher peak.

• Comparisons are made to IV doses to determine bioavailability.

  • IV doses are considered the gold standard for comparison.

Absorption Rate

• Rate of absorption is determined by parameters like Ka or T half.

  • Ka represents the rate constant.

• Rate of absorption influences peak concentration and timing.

  • Faster absorption leads to a higher and quicker peak.

• Parameters like Cmax and Tmax are used to assess absorption profiles.

  • Cmax is the maximum concentration, and Tmax is the time of peak concentration.

Pharmacokinetic Studies

• Pharmacokinetic studies focus on parameters like dose, Cmax, Tmax, and AUC.

  • These parameters are crucial for regulatory approval.

• Variability in estimates should be considered in study data.

  • Important for understanding the reliability of results.

Preclinical Work and Drug Development

• Preclinical work involves scaling up from animal studies to human trials.

  • Understanding absorption, clearance, and formulation is essential.

• Pharmacokinetics provides a quantitative framework for drug development.

  • Helps in predicting outcomes and ensuring safety and efficiency.

Conclusion

• Pharmacokinetics plays a vital role in drug development and safety.

• Understanding absorption rates, bioavailability, and variability is crucial.

• Preclinical studies and scaling up information are essential for successful drug

DD

Importance of Understanding Drug Interactions

• Link between pharmacokinetics and drug safety

• Impact of pharmacokinetic changes on medicine effectiveness

• Need for understanding pharmacology, pharmacodynamics, and AGM processes to avoid drug interactions

• Chemical and pharmacological mechanisms of drug interactions

• Prediction as a key factor in reducing drug interactions

Pharmacokinetics and Drug Concentration

• Focus on changing drug concentration through pharmacokinetics

• Achieving steady state concentration for effective and safe treatment

• Impact of drug interactions on steady state concentrations

• Consequences of sub-therapeutic or unsafe drug concentrations

Strategies for Managing Drug Concentration

• Ways to manage drug concentration with short half-life drugs

  • Adjusting dosing frequency, metabolic clearance inhibitors

• Importance of medicinal chemistry in altering drug metabolism

• Considerations for achieving higher steady state concentrations

• Deliberate strategies versus unconscious co-medication decisions

Medicine and Drug Interactions

Lack of Communication between Healthcare Providers

• Clinical pharmacologist in Christchurch uses phone to check patients' medications

  • Highlights the issue of lack of communication between healthcare providers

• Patients may be in a position where consultants are unaware of their current medications

  • Can lead to prescribing new medications without considering potential interactions

Impact of Drug Interactions

• Drug interactions can lead to adverse effects and decrease the safety and effectiveness of medications

• Various processes can affect drug interactions such as absorption, metabolism, and clearance

  • Changes in these processes can impact the concentration and effectiveness of medications over time

Importance of Drug Interaction Studies

• Drug companies take drug interactions seriously to ensure medication safety

• Animal studies may not accurately predict human responses to drug interactions

  • Differences in enzyme metabolism across species can lead to uncertainties

Clinical Evaluation of Drug Interactions

• Historically, drug interactions were evaluated empirically by administering medications together

• Preclinical evaluation involves using in vitro systems with human tissues to screen compounds

• Understanding the mechanisms behind drug interactions is crucial for drug development and safety

Future of Drug Interaction Studies

• In vitro systems allow for screening of compounds before human trials

• Understanding factors like absorption and metabolism can help predict and prevent drug interactions

• Identifying specific enzymes and transporters involved in drug metabolism is essential for ensuring medication safety

Enzyme Metabolism and Drug Interactions

• Identifying Metabolizing Enzymes

  • Enzymes like cytochrome P450 play a crucial role in metabolizing drugs.

  • Understanding which enzyme metabolizes a specific drug is essential.

• Database of Metabolized Drugs

  • Creating a database of drugs metabolized by specific enzymes helps predict interactions.

  • Knowing if a drug is metabolized by a certain enzyme can guide prescription decisions.

• Experimental Approach

  • Historically, human livers have been used to study drug metabolism.

  • Liver chunks are processed to create microsomes for enzyme activity analysis.

• Advantages of Microsomes

  • Microsomes offer stability and consistency compared to hepatocytes.

  • They provide a reliable model for studying drug metabolism and enzyme expression.

Transporters and Drug Interactions

• Transporter Phenotyping

  • Understanding transporter involvement in drug metabolism is crucial.

  • Cell models with overexpressed transporters help study drug uptake and efflux.

• Predicting Interactions

  • Reaction phenotyping helps predict drug interactions based on enzyme and transporter involvement.

  • Factors like affinity and capacity influence the likelihood of drug-enzyme interactions.

• Inhibitors vs. Substrates

  • Compounds can act as inhibitors without being substrates, impacting enzyme activity.

  • Recognizing non-substrate inhibitors is vital in drug development and interaction studies.

Kinetics and Inhibition

• Enzyme Inhibition Types

  • Reversible and irreversible inhibition affect enzyme activity differently.

  • Irreversible inhibition poses challenges as enzyme activity can only be restored by producing new enzymes.

• Irreversible Inhibition

  • Compounds like organophosphates can irreversibly inhibit enzymes, requiring enzyme regeneration for recovery.

• Medicinal Chemistry Implications

  • Understanding enzyme inhibition mechanisms is crucial for medicinal chemists in drug development.

This note summarizes the importance of identifying metabolizing enzymes, studying transporter involvement, predicting drug interactions, recognizing enzyme inhibition types, and understanding the implications for medicinal chemistry.

Main Ideas

Drug Design and Irreversible Inhibitors

• Active groups within drug molecules should be considered.

  • Avoid irreversible inhibitors unless designing one for therapeutic purposes.

  • Penicillin is an example of an irreversible inhibitor that works effectively and safely.

Drug Interaction and Therapeutic Range

• Drug interactions are usually not utilized positively.

  • Example of using cimetidine to inhibit toxic metabolite formation and increase therapeutic range.

  • Improved therapy with fewer adverse effects demonstrated in patients.

Case Study and Pharmacological History

• Example of using cimetidine to enhance therapy and reduce adverse effects in patients with a specific disease.

• Strategy of reversible inhibition to increase therapeutic range and improve patient outcomes.

• Approval of a similar strategy in recent years for COVID treatment.

Expediency in Drug Development

• Example of using ritonavir as an inhibitor to extend the half-life of a drug during the COVID pandemic.

• Expediency-driven strategy to overcome short half-life challenges in drug administration.

Pharmacokinetics and Drug Screening

• Importance of maintaining drug concentration above minimum inhibitory concentration for effectiveness.

• Screening out inducers to prevent enhanced drug clearance.

• Use of intact systems like primary human hepatocytes for drug metabolism studies.

Drug Metabolism Studies

• Utilization of probes like midazolam for studying drug metabolism.

• Complex assays to assess protein expression and catalytic activity for drug interactions.

Note

The discussion covers the importance of considering active groups in drug molecules, the use of irreversible inhibitors like penicillin, and the positive impact of drug interactions in enhancing therapeutic range. A case study illustrates the application of cimetidine to improve therapy outcomes. Additionally, expedient strategies in drug development during the COVID pandemic and the significance of drug metabolism studies using intact systems are highlighted.

Main Ideas

Importance of Transporters in Drug Disposition

• Transporters play a crucial role in drug disposition in various organs like the intestine, liver, kidney, and blood-brain barrier.

• Understanding transporters involved can impact drug concentration, efficacy, and safety.

• In vitro studies help identify routes of elimination but have limitations due to not replicating integrated physiological systems.

Significance of Enzyme Metabolism

• Enzyme metabolism, like CYP2D6, affects drug metabolism and potential interactions.

• Genetic polymorphisms in enzymes can lead to variations in drug metabolism among individuals.

• Screening for drugs metabolized by multiple pathways reduces the risk of adverse effects in poor metabolizers.

Drug Interaction Potential Assessment

• Drug companies rigorously assess drug-drug interaction (DDI) potential by studying enzyme substrates, inhibitors, and inducers.

• In vitro data on enzyme inhibition may not always translate to clinical outcomes due to complex in vivo factors.

• Aggressive screening during drug development minimizes the risk of significant drug interactions in marketed drugs.

Pharmacokinetic Considerations

• Pharmacokinetics involve chemical interactions impacting drug absorption, distribution, metabolism, and excretion.

• Pharmacological mechanisms can influence drug interactions by affecting factors like gastric emptying and absorption rates in the gastrointestinal tract.

Research on FDA Drug Approvals and DDI Potential

• Research on recent FDA drug approvals focuses on assessing DDI potential based on enzyme and transporter interactions.

• Continuous evaluation of drug interactions is crucial for drug companies and regulators to ensure drug safety and efficacy.

Note

Transporters and enzymes play vital roles in drug disposition and metabolism, impacting drug efficacy and safety. Understanding their involvement is crucial for predicting drug interactions and optimizing therapeutic outcomes. In vitro studies help identify elimination routes but have limitations in replicating complex physiological systems. Genetic polymorphisms in enzymes like CYP2D6 can lead to variable drug metabolism among individuals. Rigorous assessment of drug interaction potential by drug companies aids in minimizing risks through aggressive screening during development. Pharmacokinetics, influenced by chemical and pharmacological factors, affect drug absorption and distribution. Continuous evaluation of drug interactions in FDA-approved drugs is essential for ensuring patient safety and drug efficacy.

Main Ideas from the Transcript

Controlled-Release Morphine

• Morphine dosage and concentration should be carefully controlled to avoid respiratory depression.

• The goal is to provide enough morphine for pain relief without risking overdose.

Effects on Drug Absorption

• Certain substances can impact the absorption of drugs in the stomach by changing ionization ratios.

• Altering ionized to non-ionized ratios can significantly affect drug uptake.

Drug Interactions

• Drugs like itraconazole can unintentionally impact kidney function and decrease the elimination of other drugs like methotrexate.

• Probenecid, initially developed for gout, can inhibit the elimination of penicillin, leading to higher concentrations and improved clinical effectiveness.

Enzyme Expression and Cytokines

• Cytokines play a role in altering enzyme expression during inflammation, affecting drug metabolism.

• Decreasing disease burden with medication can restore enzyme expression levels, impacting drug clearance and steady state.

Concentration and Drug Safety

• Concentration plays a crucial role in drug safety and effectiveness.

• Screening out compounds with narrow therapeutic windows can enhance drug robustness and safety.

Pharmacokinetic Interactions

• Understanding pharmacokinetic interactions is essential for safe drug administration.

• Considering both pharmacokinetic and pharmacodynamic interactions is crucial for drugs like Propofol to ensure patient safety.

Drug Development Success

• Despite minor headlines, drug development success stories like self-editing are significant achievements in the field.

• Incremental changes in drug efficacy, even by small percentages, contribute to overall progress in drug

Genotoxicity and Mutagenicity Testing

Learning Objectives

• Explain genetic damage after drug exposure

• Describe the role of genotoxicity testing in drug development

• Compare models for assessing carcinogenic potential

Genotoxicity

• DNA damage can lead to mutations, altered chromosomes, and genes

• Consequences include cancer in somatic cells and genetic disorders in germ cells

• DNA damage can be caused by various factors like radiation and chemicals

Mutations

• Mutations are heritable changes in DNA sequence

• Mutagens cause mutations, leading to genetic disorders, infertility, and cancer

• Mutations can affect germ cells or somatic cells, whole chromosomes, or single genes

Chromosome Aberrations

• Changes in chromosome number or structure

• Aneuploidy and polyploidy are examples of chromosome number abnormalities

• Structural abnormalities include deletions, duplications, inversions, and translocations

Mutations Affecting Single Genes

• Point mutations can be base pair substitutions or small additions/deletions

• Base pair substitutions can be transitions or transversions

• Small additions/deletions can cause frameshift mutations

Consequences of Mutations

• Protein alterations due to point mutations

• Synonymous, missense, nonsense, and frameshift mutations

• Impact of mutations on protein function and structure

Mutagenicity Testing

• Involves hazard identification and mechanisms like apoptosis

• OECD guidelines list various tests for genotoxicity and carcinogenicity

• Short-term mutagenicity assays help identify DNA-damaging agents

Conclusion

• Understanding genotoxicity and mutagenicity is crucial for drug development and safety testing.

In Vitro Gene Mutation Assays (Page 18)

• The Ames test is a bacterial reverse mutation assay.

  • Detects chemicals causing DNA damage and gene mutations.

  • Uses bacteria strains with pre-existing mutations in histidine or tryptophan genes.

  • New mutations allow bacteria to grow in the absence of histidine or tryptophan.

Salmonella typhimurium and E. coli Tester Strains (Pages 19-20)

• Salmonella typhimurium strains are histidine-dependent with additional mutations for sensitivity to mutagens.

  • Rfa mutation increases cell wall permeability.

  • uvrB-bio deletion reduces DNA repair.

• E. coli strains have mutations in tryptophan operon and uvrA gene.

  • Less able to repair DNA damage.

• Salmonella strains are Biological Safety Level 2, while E. coli strains are Level 1.

Specific Mutation Events Detected (Page 21)

• Different Salmonella strains detect various mutation events.

  • Base pair substitutions, frameshifts, transitions/transversions, cross-linking.

• E. coli detects AT base-pair substitutions.

Mammalian Enzyme System and Metabolism (Page 22)

• Carcinogenic chemicals need metabolizing enzymes for activation.

  • CYP enzymes in humans metabolize chemicals to DNA-reactive forms.

• S9 from rat liver is used to add mammalian metabolizing enzymes.

  • Arochlor 1254 historically used, now replaced by other inducers.

Mouse Lymphoma Assay and HPRT Gene Mutation Assay (Page 23)

• Mouse Lymphoma Assay detects mutations in the thymidine kinase gene.

• HPRT gene mutation assay is similar but focuses on the X chromosome.

Chromosomal Alterations Tests (Pages 24-25)

• Chromosome Aberration Test detects alterations in metaphase cells.

• Micronucleus Assay detects genotoxic damage in interphase cells.

In Vivo Assays (Pages 26-27)

• In vivo chromosome aberration test in rodents.

• Unscheduled DNA Synthesis in mammalian liver cells detects DNA repair.

Big Blue® Transgenic Rodent Gene Mutation Assay (Page 28)

• Uses transgenic rodents with reporter genes to detect mutations.

• Can analyze mutations in various rodent tissues.

ICH Guidelines on Genotoxicity Testing (Pages 29-30)

• Standard battery for genotoxicity testing includes gene mutation assay and cytogenetic tests.

• Carcinogenicity studies are recommended for pharmaceuticals with continuous use over 6 months.

• Genotoxic compounds are presumed to be trans-species carcinogens and may not need long-term carcinogenicity studies.

Page 31

• Carcinogenicity Testing Guidance

  • Dose selection is crucial for safety over human exposure.

  • Consider clinical use, exposure patterns, and metabolite profile.

  • Lifespan observation of animals for about 2 years.

  • Full pathological analysis of tissues and organs at the study's end.

Page 32

• Genotoxicity Testing Guidance

  • Understanding existing information on drug safety is essential.

  • Weight of Evidence approach introduced in 2012, finalized in 2022.

  • Predicting outcomes of rat carcinogenicity study and human carcinogenicity.

Page 33

• Investigative Approaches for 2-Year Rat Study

  • Factors influencing the likelihood of conducting a 2-year rat study.

  • Different scenarios based on biologic pathways, pharmacology, histopathology, genotoxicity, immune effects.

  • Potential investigative approaches include special stains, biomarkers, clinical data.

Page 34

• Requirements prior to FIH Trials

  • Single gene mutation assay for single-dose trials.

  • Additional chromosomal damage tests for multiple-dose trials.

  • Carcin