Movement of unchanged form of drug molecules from site of administration to systemic circulation is called absorption. Various factors affect the rate of absorption they are listed as follows, Physico-chemical, Pharmaceutical and, Physiological. PHYSICOCHEMICAL FACTORS: Drug solubility and dissolution rate Particle size and effective surface area Polymorphism and amorphism Pseudo polymorphism (hydrates / solvates). Salt form of the drug. Lipophilicity of the drug – (pH partition hypothesis). pKa of the drug and pH – (pH partition hypothesis). Drug stability. PHARMACEUTICAL FACTORS: Disintegration time (tablets / capsules). Dissolution time. Manufacturing variables. Pharmaceutical ingredients (excipients / adjuvants). Nature and type of dosage form. Product age and storage conditions PHYSIOLOGICAL FACTORS: Age. Gastric emptying time. Intestinal transit time. Gastrointestinal pH. Disease states. Blood flow through the GIT. Gastrointestinal contents: Other drugs b) Food c) Fluids d)
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