GLC Determination of dl-2-(3-Phenoxyphenyl)propionic Acid (Fenoprofen) in Human Plasma

The quantitative determination of dl-2-(3-phenoxyphenyl)propionic acid (fenoprofen) in plasma is described. Fenoprofen, extracted with hexane from 1 ml. of acidified plasma, is converted to the silyl ester and then measured by GLC utilizing a flame-ionization detector. Favorable quantitation is achieved by using dl-2-(4-phenoxyphenyl)valeric acid as a mass internal standard. The assay is quantitative above 0.25 mcg./ml. Overall, precision and accuracy of the assay are approximately ±10% (RSD) and ±5% (RE) in the range of 3-8 mcg./ml. Plasma data are presented to demonstrate the clinical utility of the method.