pmcy 4200 exam 3

In order to develop medication that can be used to treat patients in a
rational way

• what effect we are trying to achieve

• whether the effect is immediate or delayed

• how much we need to give to obtain the desirable effect

• how ling the effect will last 

• what the likelihood is for unwanted effects effects to occur and how we avoid or minimize them

we need to know, in addition to the pharmacokinetics of the drug

1. the pharmacodynamics of the drugs(the relationship between the concentration and effect)

2. how the pharmacologic effect varies in individual patients

   1. the mechanism of action

therapeutic index

• most dosage regimens are based on repeated dosages at a constant interval to obtain concentrations that provide desired pharmacologic response without any side effect

  • in reality there is no absolute therapeutic range. Both the upper and lower limits are based on probabilities and will vary between individuals

Electromyography and ketamine(anesthetic)

• a technique for evaluating and recording the electrical activity produced by skeletal muscles. measured at different frequencies 

  • the median frequency of the EMG can be used as a quantitative measure of muscular pain

does the pharmacologic effect follow the plasma concentration at all times or is it more related to the average concentration?

it takes time for the drug to distribute to the site of action. after reaching the receptor the process of binding may be slow and contribute to delay in response. Then it takes time for the drug action to change the physiological intermediate substances before the drug response is observed.

why is it important to know whether the effect is instant or delayed

A delayed response mean that the effect will fluctuate less during a dosing interval and we have more flexibility when dosing a patients with less probability to see side effects or no effect

type of effects (drug interactions)

• Drug-receptor and Drug-ion channel interactions 

  • Drug-enzyme interactions

turnover of target proteins

• when the drug affects the formation or the elimination of a target protein, the clinical effect will be delayed, as the change in the pool size is dependent on the turn-over time of the protein

Placebo/Nocebo Effect

placebo - latin for “I will please” and refers to a treatment that appears real, but is designed to have no therapeutic benefit

Nocebo - A harmless substance or treatment that when taken by or administered to a patient is associated with undesirable or harmful side effects or worsening of symptoms due to negative expectations or the psychological condition of the patient

multiple dosing

steady-state is reached with multiple dosing

calculating dosing interval

loading dose = gets you to steady state faster

maintenance does = maintains steady state

therapeutic index

TI = minimum toxic concentration/minimum therapeutic concentration

adverse of drug reactions - administration of drug

• infused too quickly

• Gi distress

• irritation to skin

  • bad taste in mouth

clinical factors

• inherent person to person variability

• disease

• age and weight

  • drug-drug interactions

systemic effect

drugs administered via a route to produce therapeutic blood levels

very short half-life(<20 minutes)

therapeutic index - medium to high - constant rate administration and /or short term therapy

therapeutic index - low - not a candidate except under very closely controlled infusion

short half-life (20 minuted to 3 hours)

therapeutic index - medium to high - ratio of dosing interval to half life = 3-6 - to be give any less often than every 3 half-lives drug must have a very high therapeutic index

therapeutic index - low - only by infusion

intermediate half-life (3-8 hours)

therapeutic index - medium to high - ratio of dosing interval to half-life = 1-3 - very common and desirable regimen

therapeutic index - low - ratio of dosing interval to half life = 1 - requires 3-6 doses per day, but less frequently with controlled released formulation

Long Half-Life ( 8-24 hours)

therapeutic index - medium to high - ratio of dosing interval to half-life = 1 - very common and desirable regimen

therapeutic index - low - ratio of dosing interval to half-life = 0.5-1 - very common and desirable regimen

very long half-life (>24 hours)

therapeutic index - medium to high - ratio of dosing interval to half-life = <1 - once daily is practical. occasionally given once weekly

therapeutic index - low - ratio of dosing interval to half-life <1 - required careful control, since once toxicity is produced, drug levels and toxicity decline very slowly

peptides, proteins, antibodies and RNA as drugs

• easy to generate products aimed for targets of interest

• can often be modified to adjust PK

  • antibodies are the largest and fastest growing market of biopharmaceuticals

therapeutic proteins 

• comes in all shapes and forms, from small peptides to large monoclonal antibodies and car T-cells (living drugs)

• they vary from existing endogenous proteins to new constructs with unique characteristics 

  • in general, they are larger than small molecules but not necessarily so

peptibody fusion protein

by fusing a peptide to part or all of an antibody, a peptibody combines the biological activity of a peptide with the longer duration of activity of an antibody

oncolytic virus therapy

by deleting certain genes, viruses can be programmed to replicate in tumor cells but not in normal cells. This selective viral replication causes the tumor cells to lyse - releasing tumor-specific antigens

CAR T Cells

Therapy is provided by removing or harvesting T cells from a patient with cancer, transfecting the cells with CAR genes that are directed against the patient’s tumor type, expanding the modified T cell population, and reinfusing the cells back into the patient

CAR T-cell therapy

Remove blood from patient to get T cells → make CAR T cells in the lab → grow millions of CAR T cells → Infuse CAR T cells into patient → CAR T cells bind to cancer cells and kill them

checkpoint inhibitors in cancer treatment

• regulators of the immune system

• critical for self-tolerance to prevent he immune system for attacking endogenous cells

  • however, many cancer cells expresses the same checkpoint proteins and thereby avoid being attacked by the immune system.

types of checkpoints in cancer treatment

• CTLA-4 (cytotoxic T lymphocyte associated protein 4)

• PD-1 (programmed cell death protein 1)

• PD-L1 (programmed cell death ligand 1)

CTLA-4

Ipilmumab (yervoy) is a checkpoint inhibitor drug that blocks CTLA-4. It is a treatment for advanced melanoma and advanced renal cell cancer.

PD-1 checkpoint inhibitors

• Nivolumab (Opdivo)

• Pembrolizumab (Keytruda)

  • used to treat melanomas, hodgkin lymphoma, non small cell lung cancer, kidney cancer

PD-L1 checkpoint inhibitors

• Atezolizumab (Tecentriq)

• Avelumab(Bavencio)

• Durvalumab (lmfinzi)

  • used to treat skin cancer, lung cancer, some liver and breast cancers, cancers of the urinary tract

CTLA-4/B7

Binding inhibits T cell activation

CTLA-4

Blocking CTLA-4 allows T cell killing of tumor cell

Limitations of therapeutic antibodies

• high cost

• intracellular targets are not readily accessible

• not orally bioavailable

• inefficient delivery across the blood-brain barrier

  • inefficient tissue penetration

Kinetic considerations

• elimination of peptides and proteins is to a large degree dependent on the molecular weight and structure

  • antibodies are also eliminated via interaction with their target. kinetics of antibodies are therefore variable as it is dependent both on the concentration of the target and of the antibody

kinetic considerations cont. 

• peptides and small proteins show generally linear kinetics

• large proteins often show linear kinetics at low concentrations and saturable kinetics at higher concentrations

• antibody kinetics being also dependent on the amount of target present makes the kinetics less predictable

renal elimination of peptides and proteins 

• generally filtered by the glomerulus, we will rarely find proteins in the urine

• peptides and proteins are reabsorbed and metabolized to the constituent amino acids in the proximal tubule

  • the result is that the elimination (CL and half-life) is sensitive to renal function even though no protein is found in the urine

Hepatic uptake of peptides and proteins

• passive diffusion - if they have sufficient hydrophobicity

• pinocytosis

• receptor-mediated endocytosis

  • uptake of glycoproteins

carbohydrate side chain

proteins containing a carbohydrate side chain can be taken up by cells via certain carbohydrate receptors

glycosylation

important for elimination of proteins. different production methods can generate proteins without glycosylation or with different types of glycans

diffusion of proteins

diffusion of proteins in and out of capillaries are dependent of the molecular weight of the protein

lymphatic system

• the lymph is an open system in contrast to blood which is a closed system

• it is driven by muscle concentrations

• one of its main purposes is to maintain fluid balance and to return proteins filtered into the interstitial fluid back to blood

• approximately 3 liter of lymph is returned to blood via the subclavian veins per day

• the lymph nodes acts as filters to remove bacteria, viruses and defective proteins

  • protein absorption is slow

antibody clearance is governed by a number of different mechanisms

• specific 

• non-specific

• characteristics of antibodies 

  • other clearance mechanisms

Removal via Binding to target specific receptors

• the more target cells the faster the removal and the shorter the half-life the stronger the affinity, the faster the removal

• clearance is saturable and dose-dependent

• AUC increases disproportional with does

  • half-life changes with dose

Development of human antibodies to therapeutic antibodies

mouse (momab) > Chimeric (ximab) > Humanized (Zumab) > Human (mumab)

in general the development of antibodies increases the clearance and shortens the half-life of therapeutic antibodies

PK of small molecules

• PK usually independent of pharmacodynamics

• binding generally non-specific(can bind to a number of proteins)

• usually linear PK

• relative short half lives

• elimination by metabolizing enzymes or by excretion renal clearance often important 

  • binding to tissues, relative high V

PK of therapeutic antibodies

• PK often dependent on pharmacodynamics

• binding specific for target

• can be both linear and non-linear

• long half-lives

• metabolism by specific and non-specific clearance mechanisms. No P450s

• No renal clearance for antibodies

• distribution usually limited to blood and extracellular space, Low V

  • need parenteral dosing

Bioavailability of monoclonal antibodies

• bioavailability os usually determined if we are to administered the proteins by any other route than IV, e.g., SC.

  • Determined by the same method as for small molecules, comparing the AUC to the AUC after an IV dose

RNA oligonucleotides (ON)

can be used to interfere with protein synthesis either by blocking the production, restore protein production by inhibiting miRs, alter the splicing to correct errors in protein production or to create new isoforms

mRNA

can be used to create new proteins, as vaccines, etc.

Advantage: the effect is transient and therefore better controlled than gene therapy, works inside cells only

problems as drugs: being hydrophilic and highly bound to albumin they cross membranes with difficulties, The presence of nucleases in blood, extra cellular space and inside cells, their half-lives are often measured in seconds or minutes rather than hours and days, The immune system will sometimes identify our ON drugs as viruses and initiate an inflammatory and immune response

prolong the half life mRNA

• changes to the ON backbone - increases half-lives to days and hours

• to improve the cellular uptake, nucleotides are often conjugated with N-acetylgalactosamine that binds to the asialic acid receptor and therefore promote internalization of the compound

• positive lipid nanoparticles as vesicles for the nucleotides will also stabilize them and help them interact with cell membranes

Biopharmaceutics

The study of how the physiochemical properties of drugs, dosage forms, and route of administration affect the rate and extent of drug absorption 

Bioavailability

the rate and extent of therapeutically active drug reaching the systemic circulation

Physicochemical factors influencing bioavailability

• solubility

• solid state

• MW

• Polarity

  • Lipophilicity

Physiological factors influencing bioavailability 

• Absorption Mech.

• Gastric Residence Time

• Intestinal Motility

• Blood flow

  • Disease

Biopharmaceutical factors influencing bioavailability

• Route of Admin.

• Dosage form

• Excipients

• Drug interactions

  • dose

Transcellular

Passage through cells

Paracellular

passage between cells

Drug appearance

Drug must pass through multiple barriers to reach target site

simple diffusion

a process of mass transfer of molecules across the plasma membrane from high concentration to low concentration

no energy required

Fick’s first law 

describes the diffusion of a drug across the rate of limiting barrier of the cell - plasma membrane

the highest conc. you can reach is the solubility of the drug

permeability

the more permeable the drug, the easier it is to penetrate the plasma membrane

poor absorption or permeation

• molecular weight >500

• Log P is over 5

• more than 5 H-bond donors

  • The sum of N’s and O’s is >10 (H-bond acceptors)

factor impact of lipophilicity

lipophilicity decreases as molecules become more ionized

drug characteristics

• drugs are more soluble when ionized

• drugs are more lipophilic when unionized

  • lipophilic drugs are poorly water-soluble

diseases caused by transporter dysfunction

• tangier disease

• Dubin Johnson syndrome

  • cystic fibrosis

carrier mediated

the transporters bind to the selective solutes and undergo conformational change, then transport the molecules into the cell

ABC transporters

• large gene family

• defined by an ATPase moiety on the protein

• found in almost all absorptive, excretory, and barrier tissues

• critical for moving a wide range of physiological substances and toxins

ABCB1 - ABC transporter

multi-drug resistance; P-glycoprotein

ABCB11 - ABC transporter

Bile salt export protein

ABCC1-C9 - ABC transporter

multi-drug resistance associated

ABCG2 - ABC transporter

breast cancer resistance protein

P-glycoprotein

• a cellular efflux pump encoded by the MDR1 gene

• expressed on the apical membrane of epithelial cells in the intestine, Bile Canicular membrane of hepatocytes, kidney

• plays a role in the absorption, distribution and elimination of numerous drugs

GI - Based Drug Delivery

• preferred mode of drug administration

  • convenient for patients which improves adherence

What are the major rate-limiting steps in drug formulation at the early development phase?

Solubility and dissolution

Effect of GI Disease on drug pharmacokinetics

• primarily affect the absorption but can also influence distribution, metabolism, and excretion

Drug absorption may be affected by any disease that causes changes in:

• intestinal blood flow

• gastrointestinal motility

• changes in stomach emptying time

• gastric pH that affects drug solubility

• Intestinal pH that affects the extent of ionization

• permeability of the gut wall

• bile secretion

• digestive enzyme secretion

  • alteration of normal GI flora

Effects on drug absorption

• altered GI transit time

• rapid transit can reduce the time a drug is in contact with its absorption site, leading to decrease absorption 

• CR drugs are designed to release their active ingredients slowly over several hours

  • Poorly soluble drugs do no dissolve easily and require more time in the GI tract

  • tricyclic antidepressants and antipsychotic drugs have anticholinergic side effects and result in reduced gI motility

Effects on drug absorption 2

• Changes in GI pH - diseases or treatments

  • reduced absorptive surface area - conditions that cause inflammation to the intestinal mucusa

  • 2

effects on drug absorption 3

• altered mucosal permeability, enzymes, and transporters - inflammation and mucosal damage

  • changes in luminal contents - altered bile acid levels in Crohn’s disease

effect on distribution

• hypoalbuminemia(low albumin levels in the blood), which can occur in malnourished patients with severe IBD

  • alter the protein binding of highly protein-bound drugs

effect on metabolism

• systemic effects of chronic inflammation may affect liver and kidney function, potentially altering the metabolism and excretion of drugs

Clinical implications

• variable and unpredictable nature of these effects

• clinicians should be ware of potential issues, especially for drugs with a narrow therapeutic index

• monitoring patients for efficacy and potential adverse effects is crucial

  • dosage adjustments or alternative formulations

Hepatic function and metabolic clearance

• blood enters the liver from the hepatic artery and the portal vein

• hepatic artery delivers most of the oxygen

  • portal vein comes from the intestines and subjects orally administered drugs/nutrients to live metabolism

liver prediction

• the structure of the liver is relatively complex making it difficult to develop exact predictions of the individual factors contributing to the elimination

liver metabolism

the capacity of the liver to metabolize drugs depends on hepatic blood-flow, membrane penetration, and hepatocyte enzymes 

can be affected by liver disease

what causes increase hepatic blood flow to vary

• supine position

• food intake

• viral hepatitis

  • diarrhea

What causes decrease hepatic blood flow to vary

• upright position

• cold temp

• sever burns

• liver cirrhosis

  • propranolol

hepatic (liver) diseases

• alcoholic liver di

• disease(cirrhosis)

• chronic infections with hepatitis viruses B and C

  • drug induced hepatotoxicity is the leading cause of acute liver failure in the US

The liver disease spectrum

ranges from initial damage, such as fat accumulation, to severe, irreversible stages like cirrhosis and end-stage liver failure

Cirrhosis

a chronic liver disease characterized by the formation of scar tissue (fibrosis) in the liver

dosage considerations in hepatic disease

• liver disease can modify the kinetics of drugs biotransformed by the liver

  • in liver disease, protein synthesis may be reduced

liver dysfunction may:

• reduce the clearance of drugs eliminated by hepatic biotransformation and/or biliary excretion

  • affect plasma protein binding which in turn could affect the processes of distribution and elimination

hepatic disease may lead to:

• drug accumulation

• failure to form an active or inactive metabolite

• increased bioavailibitly after oral administration

  • alteration in drug-protein binding

effects of liver disease on ADME

• delayed gastric emptying or increase gastric transit time

• reduced protein synthesis causes fewer available binding sites for drugs

• increased free fraction of highly protein-bound drugs

• reduced enzyme activity

• decreased hepatic blood flow

• impaired biliary excretion

• renal impairment