JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD Pharm. D IV Year BIOPHARMACEUTICS AND PHARMACOKINETICS Previous Question Paper (October - 2020 - R08)

Factors affecting drug absorption from the gastrointestinal tract can be classified into three categories:

• Physicochemical factors: Drug solubility, dissolution rate, particle size, polymorphism, salt form, lipophilicity (log P), and pKa of the drug.
• Physiological factors: Gastrointestinal pH, gastric emptying rate, intestinal motility, blood flow to the GI tract, and the presence of food or other components in the lumen.
• Formulation factors: Type of dosage form (e.g., solution vs. tablet), excipients used (binders, disintegrants, surfactants), and the manufacturing process.

Protein binding significantly influences the pharmacokinetics and pharmacodynamics of a drug:

• Distribution: Only the free (unbound) fraction of the drug is pharmacologically active and capable of crossing biological membranes to reach the site of action.
• Reservoir effect: Plasma proteins act as a storage depot, releasing the drug as the free concentration drops, which prolongs the drug's duration of action.
• Elimination: Protein binding restricts the glomerular filtration of drugs, thereby slowing down the rate of renal excretion.
• Drug interactions: Displacement of one drug from its protein-binding site by another agent can lead to a sudden increase in the free concentration of the displaced drug, potentially causing toxicity.