Second lecture 29/9/2008

By the end of this lecture you have to:
* Understand why there is a difference between the in vivo and in vitro results of biological activity.
* Understand that variation in biological activity is not always a matter of drug-receptor affinity or intrinsic activity.
* Know that bioavailability of the drug is a key factor in determining the therapeutic efficacy of the drug.
* Correlate between drug solubility, pKa, logP and its pharmacokinetic profile (site of action, duration of action,...etc.).
* Know how to, structurally, modify a drug so as to change its physicochemical properties and hence change or improve its therapeutic use.

Here are some T/F questions from previous exams:
1- The physicochemical properties of I.V. general anesthetics are important in that they affect ADME of the drug.
2- Micronized griseofulvin has better dissolution and absorption than regular griseofulvin.
3- High molecular weight dugs are absorbed by convective absorption.
4- Barbital and secobarbital have similar absorption rates since they have similar pKa values.
5- It is always required that drugs have high partition coefficient to ensure better absorption from GIT.
6- Neutral fat, unlike plasma protein, is regarded as a storage site for hydrophobic drugs.

Answers will be:
1- (F) because IV drugs are not absorbed through membrane barriers.
2- (T)
3- (F) it is only low MW drugs that are absorbed by convective absorption.
4- (F) because they differ in their part.coeff.
5- (F) because some drugs are required to act locally in the GIT eg. succinyl sulfathiazole.
6- (T) storage in neutral fat depends on the lipophilicity of the drug but plasma protein binding depends on the structure of the drug not lipophilicity.