Pharmacokinetics 🏥2

Question 1

Drug Absorption

Answer 1

Transfer of a drug from its site of administration to the bloodstream, with rate and efficiency depending on the route of administration.

Question 2

Bioavailability

Answer 2

Defined as the proportion of a drug that enters systemic circulation when introduced into the body, affected by factors like route of administration.

Question 3

Drug Distribution Factors

Answer 3

Factors include blood flow, drug binding to plasma proteins, drug tissue binding, and drug liposolubility.

Question 4

Drug Metabolism

Answer 4

Metabolism of lipophilic drugs into hydrophilic metabolites is necessary for excretion and termination of biological activity.

Question 5

Phase I reactions

Answer 5

Phase I reactions generally result in the conversion of the parent drug to a more polar metabolite, leading to inactive metabolites.

Question 6

Blood-Brain Barrier

Answer 6

The barrier restricts penetration of polar molecules into the brain; drugs must be liposoluble or have active transport for CNS entry.

Question 7

Phase II reactions

Answer 7

Phase II reactions involve conjugation reactions where a covalent bond is formed between the drug molecule and compounds like glucuronate, acetate, glutathione, amino acids, or sulfate.

Question 8

Enzyme induction

Answer 8

Some cytochromes P450 are inducible by certain drugs, leading to increased transcription and potential clinical consequences like altered drug metabolism.

Question 9

Factors Influencing Drug Absorption

Answer 9

pH effect, surface area available, blood flow to absorption site, contact time, and involvement of P-glycoprotein all influence the absorption of drugs.

Question 10

Weak Acid Properties

Answer 10

Weak acids like aspirin are more liposoluble in their protonated (uncharged) form, HA.

Question 11

Applications of H-H Equation

Answer 11

One application is ion trapping for drug excretion manipulation by adjusting urine pH.

Question 12

Liver in drug metabolism

Answer 12

The liver is the main organ for drug metabolism and plays a crucial role in the first-pass effect.

Question 13

Drug excretion

Answer 13

Metabolism enhances the hydrophilicity of drugs and their metabolites, aiding in drug excretion, with renal excretion being the most common mechanism.

Question 14

First-Pass Effect

Answer 14

Fraction of ingested drug metabolized in the gut wall and liver before reaching systemic circulation, impacting drug absorption.

Question 15

Routes of Drug Administration

Answer 15

Include enteral routes (oral, sublingual, rectal) and parenteral routes (IV, IM, SC, ID), each affecting drug absorption differently.

Question 16

H-H Equation

Answer 16

The Henderson-Hasselbalch Equation is used to calculate the pH of a buffer solution and the ratio of the conjugate base to weak acid.

Question 17

Cytochrome P450

Answer 17

Most phase I reactions are catalyzed by the cytochrome P450 system, a superfamily of heme-containing isozymes responsible for metabolizing 80% of drugs in clinical use.

Question 18

Enzyme inhibition

Answer 18

Certain drugs can inhibit cytochromes P450, leading to decreased drug metabolism and potential drug toxicity due to elevated drug concentrations.