Drug Distribution in Biopharmaceutics

Drug Distribution in Biopharmaceutics explains how drugs move from blood to tissues, influenced by protein binding and permeability.

Definition of Drug Distribution in Biopharmaceutics

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

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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