Page 20 - controlled drug delievery

II- Biological Factors

5- Metabolism

• Poor candidates for Oral SR/CR formulation are:
• Drugs suffering significant pre-systemic metabolism either in the

gut lumen or tissue (e.g. nitroglycerin) or due to first pass effect
(e.g. propranolol, diltiazem); Why?
 Because the drug is slowly introduced to the metabolizing
enzymes allowing more complete metabolic conversion.
Consider the formulation of :
1. Oral SR Formulation of Levodopa; the drug is metabolized by

intestinal dopa decarboxylase?
Formulate with dopa-carboxylase inhibitor
use an enzymatically stable prodrug