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Protein Availability and Drug Dosing

Drug-binding proteins in serum can fluctuate in disease states.

For example, if albumin levels fall, as can occur in liver failure or nephrotic syndrome, less albumin will be available for drug binding. If this happens a new dose of drug may produce a toxic concentration of free drug since albumin is now lower.

The image on the right illustrates the loss of equilibrium between a protein-bound drug and a free drug when drug-binding proteins are diminished.

Doses of drugs that are highly protein-bound may need to be adjusted in patients with lower drug-binding protein levels.

Examples of some common drugs that are highly protein-bound include thyroxine, warfarin, diazepam, heparin, imipramine and phenytoin.