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Drug Distribution in Biopharmaceutics

Definition

Drug distribution refers to the process by which a drug is transported from its administration site to target tissues and other organs in the body via the bloodstream.

Factors Influencing Distribution

  • Physicochemical properties (lipophilicity, molecular size)

  • Tissue composition (fat, muscle, water content)

  • Plasma protein binding (e.g., albumin)

  • Transporters and receptors (facilitate or hinder drug movement)

Importance of Distribution

  • Affects drug efficacy—poor distribution to the target site reduces effectiveness.

  • Influences drug safety—excessive distribution to non-target tissues may cause side effects.

Steps in Drug Distribution

Steps in Drug Distribution

  1. First-Pass Metabolism (for oral drugs): Drug is metabolized in the liver before entering systemic circulation.

  2. Transport to Tissues: Drug circulates in the bloodstream and reaches various organs.

  3. Plasma Protein Binding: Some drugs bind to proteins like albumin, affecting availability.

  4. Tissue Diffusion: Drugs move into interstitial fluid and cells based on lipid solubility and concentration gradients.

  5. Metabolism & Elimination: The drug undergoes enzymatic metabolism and is excreted via the kidneys or bile.


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