JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD Pharm. D IV Year BIOPHARMACEUTICS AND PHARMACOKINETICS Previous Question Paper (October/November - 2019 - R08)

Biopharmaceutics is the study of the interrelationship between the physicochemical properties of the drug, the dosage form in which the drug is given, and the route of administration on the rate and extent of systemic drug absorption.

Passive Diffusion: This is the most common mechanism, where the drug moves from a region of higher concentration to lower concentration across the lipid bilayer of the cell membrane. It is a non-energy-dependent, non-saturable process that follows Fick's first law of diffusion, where the rate of transport is proportional to the concentration gradient.

Active Transport: This process involves the movement of drug molecules against a concentration gradient, requiring energy in the form of ATP and specific carrier proteins. It is characterized by being saturable, selective for specific structural analogs, and capable of being inhibited by metabolic poisons or competitive inhibitors.

Drug absorption from the gastrointestinal tract (GIT) is influenced by several factors:

• Physicochemical Factors: Drug solubility and dissolution rate are primary; poorly soluble drugs often show limited absorption. The pH-partition hypothesis states that only the unionized form of a drug can permeate the lipid membrane. Particle size reduction (micronization) increases surface area and enhances dissolution.
• Pharmaceutical Factors: The type of dosage form (e.g., solution vs. tablet), excipients, and manufacturing variables like compression force and binder concentration significantly affect disintegration and dissolution.
• Physiological Factors: Gastric emptying rate is critical; faster emptying generally leads to faster absorption. Intestinal transit time, blood flow to the GI tract, and the presence of bile salts or food can either enhance or delay drug absorption.
• Patient-related Factors: Age, disease states (e.g., achlorhydria, malabsorption syndromes), and concurrent administration of other medications can alter the GI environment and affect the bioavailability of the drug.