pharmacokinetics and drug action

Question 1

what is pharmacokinetics.

Answer 1

A science that deals with the study and kinetics of the absorption, distribution, metabolism and excretion (ADME) of the drug. It also includes study of associated toxicity.

Question 2

what is absorption.

Answer 2

The process through which the drug moves from its site of administration into the systemic circulation.

Question 3

why are lipid soluble non polar drugs absorbed faster.

Answer 3

Smaller molecules diffuse faster than large molecules.

Question 4

why does most absorption occur in the intestine.

Answer 4

The area in the stomach is far smaller than that of the intestine.

Question 5

How are drugs that are completely insoluble in water absorbed.

Answer 5

Such drugs behave as fat globules, which are emulsified into smaller particles by bile salts secreted from the liver so that they can be absorbed in the intestines e.g. vitamins

Question 6

what is distribution

Answer 6

Distribution is the movement of drug molecules throughout the body to reach their site of action.

Question 7

what is the degree of distribution dependent on. (2)

Answer 7

1. lipophilicity of the drug

2. local blood flow to tissues

Question 8

what is metabolism or biotransformation.

Answer 8

This is the process of transformation of a drug into water-soluble metabolites within the body so that it can be easily excreted out by the kidneys,

Question 9

explain the phase 1 and phase ii types of metabolism.

Answer 9

phase I- includes the enzymes that biotransform the drug chemically by processes such as oxidation, reduction and hydrolysis or by removing and adding an active group
Phase II - includes the conjugation of a drug or metabolite of phase I with a polar group to make its excretion possible.

Question 10

what is excretion.

Answer 10

The removal of substances from the body.

Question 11

what is bioavailability.

Answer 11

Bioavailability is the rate and extent of absorption of the drug from dosage form into the systemic circulation or receptor site.

Question 12

what is the order of the bioavailability of orally administered drugs.

Answer 12

oral solutions - oral suspensions - capsule - tablet - coated tablet

Question 13

what factor influences the delivery of drugs from the systemic circulation to the target tissue/organ

Answer 13

whether the organ has a high or low perfusion rate.

physiochemical properties since they affect the permeability of the drug to various tissues.

Question 14

why can lipid-soluble drugs get accumulated in organs or tissues

Answer 14

they have a high partition coefficient and non polar nature

Question 15

what is the primary site in the body for drug metabolism and why is it.

Answer 15

smooth endoplasmic reticulum of the liver cell.

This is because the liver contains large amounts of many varieties of enzymes.

Question 16

Effects of drug metabolism.

Answer 16

1. Pharmacological inactivation of drugs.. metabolism results in drug metabolites that have little or no pharmacological activity.
2. Toxicological activation of drugs. The metabolites formed after the biotransformation process have a high tissue reactivity, thereby causing tissue toxicity, which may cause necrosis(death of tissue), hepatitis etc.
3. Pharmacological activation of drugs. Prodrugs (inactive) are metabolized to highly active drugs. Prodrugs when taken are inactive and get transformed into their active form after metabolism.

Question 17

what are the principle processes that determine the urinary excretion. (3)

Answer 17

1. Glomerular filtration.
2. active tubular secretion.
3. active of passive tubular reabsorption

Question 18

what does passive diffusion in the passive tubular reabsorption depend on (2)

Answer 18

lipid solubility

ionization of the drug at the existing urinary PH.