Pharmacokinetics: Absorption, Distribution, Metabolism, and Excretion of Drugs

Drug Distribution: Plasma Protein Binding, Tissue Permeability, and Volume of Distribution

Pharmacokinetics is the study of how drugs move through the body, including absorption, distribution, metabolism, and excretion. One of the most important aspects of pharmacokinetics is drug distribution, which determines the extent and speed at which a drug reaches its target tissues.

Plasma Protein Binding

Many drugs bind to plasma proteins, such as albumin, which affects their bioavailability and therapeutic effects. Highly protein-bound drugs remain in circulation longer, while unbound drugs exert their pharmacological action.

Tissue Permeability

Drug permeability into tissues is influenced by factors such as lipid solubility, molecular size, and active transport mechanisms. Lipophilic drugs readily cross cell membranes, whereas hydrophilic drugs may require transport proteins.

Volume of Distribution (Vd)

Volume of distribution (Vd) quantifies the extent of drug dispersion in the body. A high Vd indicates extensive tissue distribution, while a low Vd suggests confinement to plasma. This parameter affects dosing regimens and therapeutic monitoring.

Conclusion

Understanding drug distribution mechanisms helps optimize pharmacotherapy, ensuring effective treatment while minimizing toxicity. Factors such as protein binding, tissue permeability, and Vd play critical roles in drug behavior within the body.