A drug can change a laboratory reaction even when the assay measures the breakdown of a different substance. Ascenzi and colleagues studied this distinction in an experiment with purified human serum albumin.
The investigators measured the hydrolysis of three 4-nitrophenyl esters. Diazepam was one of five compounds they tested as inhibitors. Under the tested conditions, the inhibition behaved competitively. The authors interpreted the result in terms of ligand binding in the FA3–FA4 cleft of albumin, near the tyrosine residue involved in the reaction.
The measured reaction was ester hydrolysis by albumin under controlled conditions. It was not a measurement of how fast patients eliminated diazepam. When citing the paper, identify the substrate, the protein, and the experimental conditions. A claim about a patient’s drug concentration requires evidence that addresses disposition in a relevant biological system.