Question

Provide five reasons for why plasma concentrations of a drug taken orally (P.O.) can be significantly different among individuals taking the same dose. Answers must be detailed, complete sentences, and provide a short example.

Answer 1

1.Gastric emptying time among individuals varies and faster gastric emptying accelerates during absorption in general.

2.Presence of food in stomach, dilutes the drug and retards absorption time among individuals as food delays gastric emptying.

3.Certain drugs are degraded in gastrointestinal tract as enteric coated tablets and sustained release preparations, where a gastric disease retards the rate of absorption among individuals.

4.Oral absorption of certain drugs is low and differ among individuals, because a fraction of absorbed drug is extruded back into intestinal lumen by efglux of transporter P-gp located in gut epithelium.

5.Absorption of a drug can also be affected by other comcurrently ingested drugs in each individual.

6.First pass metabolism of every individual show a great variation particularly in those with any severe liver disease and affects their absorption and plasma comcentration.

Example:

Tetracyclines are the antibiotics given in some situations to treat infections and the plasma concentration of this antibiotic is achieved by proper absorption of the drug which varies in different individuals, especially when an individual takes tetracycline along with milk.The calcium in the milk delays gastric emptying, thus retarding its absorption.