What role do plasma proteins play in drug distribution?

Plasma proteins play a crucial role in drug distribution by binding to various drugs and thereby affecting their free (active) concentration in the bloodstream. When a drug binds to plasma proteins, it becomes inactive because it is not available to exert its pharmacological effect on target tissues. This binding can influence both the distribution and elimination of the drug from the body.

For instance, a drug that is highly bound to plasma proteins may have a prolonged half-life because only the unbound or "free" form of the drug is available for metabolism and excretion. Moreover, variations in plasma protein levels, which could arise from conditions such as liver disease, malnutrition, or pregnancy, can significantly impact drug efficacy and safety.

This mechanism is essential for understanding pharmacokinetics and the appropriate dosing of medications, as well as potential drug interactions that can occur when multiple drugs compete for binding sites on plasma proteins. To summarize, the ability of plasma proteins to bind drugs and thus modulate their active concentration is fundamental in pharmacology.