Page 100 - Interactive Theoritical Notes of Bioharmaceutics and pharamcokinetics.docx compressed

PharmD clinical pharmacy program Level 3, Semester 2 Biopharmaceutics & Pharmacokinetics (PT608(

4. Intestinal motility and transit time

The drug must have a sufficient time (residence time) at the absorption site for optimum

absorption.

In the case of high motility in the intestinal tract, as in diarrhea, the drug has a very short

residence time and less opportunity for adequate absorption.

Intestinal residence is important in the following cases;

➢ Controlled and sustained release preparation

➢ Enteric coated dosage forms

➢ Slowly dissolved drugs

➢ Drugs absorbed by carrier mechanism.

5. Drug stability in GIT

Drugs may be chemically degraded and metabolized in the GIT that result in decreasing

of the bioavailability. For example,

➢ Penicillin, erythromycin, and azithromycin undergo acid catalysis hydrolysis

in gastric fluid.

➢ Some drugs as chloropromazine, progesterone and testosterone are

susceptible to enzymatic hydrolysis by enzymes located in the GIT.

99