GLC Determination of Ibuprofen [(±)-2-(p-Isobutylphenyl)propionic Acid] in Plasma

To evaluate the pharmacokinetics and drug availability from various dosage formulations, a method for the determination of ibuprofen [(±)-2-(p-isobutylphenyl)propionic acid] in human plasma was required. A simple, rapid, sensitive, and specific procedure, based on a benzene extraction of the acidified specimen and subsequent GLC analysis of the methyl esters of the extract residue, was developed. The method is sensitive to 0.5 μg ibuprofen/ml plasma. Statistical analyses indicate an average recovery of 94.8 ±6.6% (SD), which is adequate to differentiate assay error from normal biological variation. Mass spectrometric analysis, in conjunction with GLC, confirmed the specificity of the method for intact drug. The procedure was successfully applied to drug absorption studies in humans.