Question

Explain the volume of distribution and its importance in pharmacology. If Vd of a drug is 35 L, in which compartments does the drug distribute in?

4. What occurs when a drug depresses the activity of CYP enzymes? (max with 4-5 sentences).

Answer 1

#Volume of distribution of drugs and its importance.

before understanding it you have go what is PHARMACODYNAMICS & PHARMACOKINETICS ?

PHARMACOKINETICS -to make it easy to remember, it is what body does to drug - Definition is drug movement in thr body,through the body and out of the body.

- it includes ABSORPTION, DISTRIBUTION, METABOLISM and EXCRETION.

PHARMACODYNAMICS-similarly, it is what drug does in over body - it is study of drug effects and its side effects.

#Now coming to your Question.

Q-1 Volume of distribution of drugs and its importance.

Once any drug reaches to blood. ia different route of absorption then it starts distributing in different tissue like heart, brain, fat, muscle, liver etc, this depends on following

1) lipid solubility, - more the lipid soluble drug more is it diffusion into tissue.

2) ionization at physiological pH - non-ionized drug can easily get transfer into tissue.
3) extent of drug to bind to plasma and tissue proteins -transport make drug easy to reach at its target.

4)differences in regional blood flow. - more is the blood flow to organ more drug can enter into that organ.

Importance to know this is to make us easy to understand that knowing about property of different drug and comparing it to understand why they behave such so.

Q-2 Vd of drug is 35L, in which compartment does the drug distribute?

Vd literally means apparent volume of distribution

Vd = totzl drug in body / drug blood plasma concentration

so Vd represents the degree of drug distribution in body TISSUE

Higher the Vd high is tissue distribution

So here in Q Vd is 35 so it is maximum in TISSUE COMPARTMENT and less in plasma.

Q-3 What occurs when drug depress CYP enzymes activity?

So let us first understand about what are CYP enzymes. these are different enzymes in liver which metabolize drugs.

-There are different drug which either induces or inhibits CYP enzymes, so if induced than the effective drug gets metabolized faster and so decreases efficacy of drug, Similarly if drug inhibits CYP enzymes, effective drug gets metabolized slower and so increases efficacy of drug,

eg. of some drugs causes inhibitions/depresses CYP activity are - Allopurinol, erythromycin, clarithromycin, ketoconazole, metronidazole etc

eg. of drug causing CYP induction - Phenytoin, phenobarbitone, rifampin.

so the answer to this Q is that when drug depress CYP activity it causes decreases in effective drug metabolism and so the efficacy of effective drug increases.