JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD Pharm. D IV Year BIOPHARMACEUTICS AND PHARMACOKINETICS Previous Question Paper (June/July - 2022 - R08)

Absorption is the process by which a drug proceeds from the site of administration into the systemic circulation. Drugs are absorbed from the gastrointestinal tract (GIT) primarily through the following mechanisms:

• Passive Diffusion: The most common mechanism, where drug molecules move from a region of higher concentration to lower concentration across the lipid membrane.
• Carrier-Mediated Transport: Involves specialized transport proteins (facilitated diffusion or active transport) to move drugs that are polar or too large for passive diffusion.
• Endocytosis: The engulfment of large or macromolecular drugs by the cell membrane to form vesicles.
• Paracellular Transport: Movement of small, water-soluble drugs through the aqueous pores or tight junctions between epithelial cells.

Protein binding significantly influences the distribution and pharmacological activity of drugs. Key factors affecting this process include:

• Drug-related factors: Physicochemical properties such as lipophilicity, degree of ionization (pKa), and the concentration of the drug in the plasma.
• Protein-related factors: Variations in the concentration of plasma proteins like albumin (for acidic drugs) and alpha-1-acid glycoprotein (for basic drugs), often altered by disease states like cirrhosis or nephrotic syndrome.
• Drug-Drug Interactions: Competitive binding where two drugs compete for the same binding site on a protein, potentially displacing one and increasing its free (active) fraction.
• Physiological/Pathological factors: Conditions like uremia, malnutrition, or aging can alter protein structure or concentration, thereby changing the binding affinity.