Pharmacology: Absorption & Distribution

A comprehensive set of flashcards covering key concepts related to Pharmacokinetics, focusing on drug absorption, distribution, and related physiological factors.

What is Pharmacokinetics (PK)?

The quantitative study of how the body interacts with administered substances during exposure.

List the four key processes of Pharmacokinetics.

Absorption, Distribution, Metabolism, and Excretion.

What does ADME stand for in pharmacokinetics?

Absorption, Distribution, Metabolism, and Excretion.

What is the role of the small intestine in drug absorption?

It is the major site of drug absorption due to its large surface area.

What is the first-pass effect?

The metabolism of a drug in the liver before it reaches systemic circulation.

What is bioavailability?

The rate and extent of a drug reaching systemic circulation after administration.

What does P-glycoprotein (P-gp) do?

It is an efflux pump that extrudes drugs and xenobiotics out of cells, affecting absorption.

How does the pH-partition hypothesis affect drug absorption?

It states that a drug only passively crosses membranes in an unionized form.

What are carrier-mediated transporters?

Proteins that facilitate the movement of drugs across cell membranes using specialized pathways.

What is the role of albumin in drug distribution?

Albumin binds to drugs and restricts their uptake into target sites.

Define volume of distribution (V).

It characterizes the distribution of drugs between intravascular and extravascular spaces.

What happens to drug absorption when gastric emptying rate (GER) is prolonged?

It improves the quality and quantity of drug absorption.

What is the significance of fraction unbound (fu)?

It measures the extent of drug-plasma protein binding, affecting pharmacological activity.

How does molecular size affect drug permeability?

Permeability drops as molecular weight increases, particularly beyond 500 g/mol.

What is facilitated diffusion?

Transport of molecules across a membrane along the concentration gradient without energy.

What factors influence the pharmacokinetic processes?

Drug, physiological, and disease factors can influence absorption, distribution, and bioavailability.

What is the difference between absolute and relative bioavailability?

Absolute bioavailability compares bioavailability against IV, while relative compares formulations of the same drug.

How do diseases affect gastrointestinal function?

Diseases can accelerate intestinal peristalsis, alter gut flora, and affect drug metabolism.

What is the clinical relevance of the first-pass effect?

It necessitates larger oral doses compared to intravenous administration.

Explain the term 'drug distribution'.

The transfer of drug from the bloodstream to different parts of the body.

What is the effect of lipophilicity on drug permeability?

Higher lipophilicity generally increases permeability across membranes.

What types of drugs bind to alpha1-acid glycoprotein?

Lipophilic amines, like β-blockers and antidepressants, have a selective affinity for this protein.

What is a drug's half-life?

The time required to eliminate the drug concentration in the body by 50%.

How does the drug size influence its distribution?

Smaller drugs typically have better permeability and can distribute more readily.

What are the implications of the pharmacokinetic parameter 'clearance'?

Clearance determines how quickly a drug is eliminated from the body.

Describe active transport in drug movement.

Movement of molecules against concentration gradient using energy (ATP).

What are the consequences of high protein binding for a drug?

It may restrict the drug's distribution and pharmacological activity.

How does the blood-brain barrier affect drug delivery to the CNS?

Only select drugs with appropriate properties can pass through, influencing CNS drug efficacy.

What factors contribute to drug barriers in tissue distribution?

Permeability issues and blood flow rates (perfusion) affect drug distribution.

What is a characteristic of first-generation antihistamines?

They can cross the blood-brain barrier, often causing sedation as a side effect.

What factor increases the absorption rate of oral drugs?

Liquid formulation absorbs faster than solid oral formulations.

What happens when pH > pKa for weak acidic drugs?

The drug becomes ionized, affecting its ability to cross membranes.

What is the role of cytochrome P450 enzymes in drug metabolism?

They are responsible for the pre-systemic metabolism of drugs in the liver.

What is the relationship between volume of distribution and half-life?

Smaller volume of distribution corresponds to shorter half-life and faster elimination.

Why do drugs with larger molecular weight require special administration routes?

They may have limited absorption through oral routes due to their size.

What is the clinical significance of using the term 'bioavailability' in pharmacology?

It helps in determining the effective dose of a drug when entered systemically.

How does increased intestinal motility affect drug absorption?

It may decrease the time for drugs to be absorbed, reducing overall absorption.

Explain the relationship between drug pKa and ionization.

The pKa influences whether a drug will be ionized or unionized in various body environments.

What does 'tissue perfusion' refer to in pharmacokinetics?

The blood flow rate to organs affects how quickly drugs can distribute through the body.

Why is it important for drugs to remain unionized for absorption?

Unionized drugs can more easily cross cell membranes and enter systemic circulation.

What challenge do efflux transporters present for drug absorption?

They can pump drugs back into the intestinal lumen, reducing absorption efficiency.

What are the consequences of impaired liver function on drug metabolism?

Lower levels of plasma proteins can increase unbound drug concentration, affecting drug action.

Why is the understanding of pharmacokinetics critical in drug development?

It informs dosing regimens and therapeutic effectiveness based on how drugs behave in the body.

What is the significance of the area under the curve (AUC) in pharmacokinetics?

It reflects the total drug exposure over time and is used to calculate bioavailability.

How do physiological factors alter drug absorption?

Factors like blood flow, gastrointestinal pH, and presence of food can significantly change absorption rates.

Explain the effect of substrate specificity of drug transporters on drug absorption.

Transporters may preferentially allow some drugs to cross membranes while excluding others.

What determines whether a drug is 'bounded' or 'unbounded' in plasma?

It depends on the affinity of the drug for plasma proteins like albumin and alpha1-acid glycoprotein.

What is the main impact of drug carrier systems on pharmacokinetics?

Carrier systems can manipulate how drugs are absorbed, distributed, and eliminated.

How can formulation and route of administration influence bioavailability?

Different formulations (e.g., tablets vs liquids) have variable absorption rates impacting bioavailability.

What are some examples of physiological abnormalities affecting drug absorption?

Conditions like gastrointestinal inflammatory diseases can alter absorption mechanisms.

Define systemic circulation in the context of pharmacokinetics.

The pathway in which absorbed drugs are distributed throughout the body via the blood.

What physiological parameter does the term 'perfusion' relate to?

It relates to the rate of blood flow to the organs, influencing drug distribution.

What happens to drug absorption with the presence of food?

Food can both enhance and impair drug absorption depending on the drug and formulation.

How does renal function impact drug clearance?

Impaired renal function can lead to decreased clearance, extending the drug's half-life.

What role does drug solubility play in oral bioavailability?

Higher solubility often leads to better absorption and bioavailability in the body.

What is the relevance of understanding pharmacodynamics in relation to pharmacokinetics?

It helps in evaluating drug efficacy and safety by linking drug concentration to its effect.

How does the route of administration influence the onset of drug action?

Intravenous administration offers the fastest onset, while oral routes are generally slower.

Why might some drugs be less effective in patients with liver disease?

Altered metabolism and decreased protein production affect the drug's efficacy and safety profile.

What is the function of drug plasma levels in determining therapeutic efficacy?

Monitoring plasma levels helps to ensure effective dosage while avoiding toxicity.

What is the importance of knowing a drug's clearance and half-life during treatment?

These parameters guide dosing schedules and help avoid potential drug accumulation.

Describe how the hepatic portal vein relates to first-pass metabolism.

It carries absorbed drugs from the intestines to the liver for initial metabolism before systemic circulation.