plasma protein binding

Full Definition

Extent to which a medication attaches to proteins in blood plasma, affecting the amount of free (active) drug available to reach target tissues. In psychopharmacology, highly protein-bound drugs are more susceptible to drug interactions when competing for the same binding sites, and conditions affecting protein levels (malnutrition, liver disease, aging) can alter free drug concentrations. Only unbound drug is pharmacologically active, so changes in protein binding can significantly affect therapeutic response and toxicity risk.

Usage

Usage note: Often expressed as a percentage (e.g., '95% protein bound'). Remember only free drug is active.

In Context

• "High plasma protein binding explained the drug interaction when albumin levels were low." — Clinical pharmacology report
• "Changes in plasma protein binding affected the patient's response to the psychiatric medication." — Clinical case study