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 an area of higher concentration to an area of lower concentration across the lipid bilayer. It is a non-energy-requiring, non-saturable process that follows Fick's first law of diffusion. The rate of transport is directly proportional to the concentration gradient, lipid solubility, and surface area of the membrane.

Active Transport: This process involves the movement of drug molecules against a concentration gradient (from low to high concentration). It requires energy in the form of ATP and specific carrier proteins. This mechanism is saturable, shows structural specificity, and can be inhibited by metabolic poisons.

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

• Physicochemical factors: Drug solubility and dissolution rate are primary determinants. The pH-partition theory states that only the unionized form of a drug can permeate the lipid membrane. Smaller particle size increases surface area, enhancing dissolution.
• Biological factors: Gastric emptying rate significantly affects absorption; faster emptying generally leads to faster absorption for drugs absorbed in the small intestine. Intestinal transit time, the presence of food, and the surface area of the absorbing membrane also play critical roles.
• Formulation factors: The type of dosage form (e.g., solution vs. suspension), the presence of excipients (binders, lubricants, disintegrants), and the manufacturing process (granulation, compression force) dictate the release rate of the drug.
• Patient-related factors: Age, disease states (e.g., achlorhydria, malabsorption syndromes), and blood flow to the GI tract can alter the rate and extent of drug absorption.