JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B.Pharmacy IV Year BIOPHARMACEUTICS AND PHARMACOKINETICS Previous Question Paper (December – 2023/ January - 2024 - R17)

Pharmacokinetics is the study of the time course of drug absorption, distribution, metabolism, and excretion (ADME) in the body, essentially describing what the body does to the drug.

Pharmacodynamics is the study of the biochemical and physiological effects of drugs on the body and their mechanisms of action, essentially describing what the drug does to the body.

The first-pass effect, also known as presystemic metabolism, refers to the phenomenon where the concentration of a drug is greatly reduced before it reaches the systemic circulation. This occurs primarily when an orally administered drug is absorbed from the gastrointestinal tract and transported via the portal vein directly to the liver.

Key aspects of the first-pass effect include:

• Hepatic Metabolism: The liver acts as the primary site where enzymes, such as cytochrome P450, metabolize a significant fraction of the drug into inactive metabolites before it enters the systemic circulation.
• Bioavailability Reduction: Because a portion of the drug is eliminated during this initial passage, the overall bioavailability of the drug is decreased compared to intravenous administration.
• Clinical Significance: Drugs with a high extraction ratio (e.g., propranolol, nitroglycerin) exhibit extensive first-pass metabolism, requiring higher oral doses or alternative routes of administration (such as sublingual or transdermal) to bypass the liver and achieve therapeutic plasma concentrations.