DIRECT DETERMINATION OF IBUPROFEN AND IBUPROFEN ACYL GLUCURONIDE IN PLASMA BY HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHY USING SOLID-PHASE EXTRACTION

A method for the simultaneous determination of ibuprofen and its labil e, reactive metabolite, ibuprofen acyl glucuronide, in plasma is descr ibed. Reversed-phase high-performance liquid chromatography (HPLC) emp loyed a C18 column using methanol-10 mM trifluoroacetic acid as the mo bile phase with ultraviolet detection at 225 or 214 nm. It is essentia l that blood is handled rapidly and plasma is acidified upon collectio n prior to freezing. Plasma samples first are deproteinated with aceto nitrile, the supernatant is diluted with phosphate buffer, and ibuprof en, ibuprofen glucuronide, and ibufenac (internal standard) are initia lly isolated by solid-phase extraction on C18 cartridges. Upon elution , the residue is evaporated, dissolved and injected onto the HPLC syst em. Recovery is 94 +/- 8 and 70 +/- 9% for ibuprofen glucuronide and i buprofen, respectively. The measurable concentration range is linear f rom 0.1 to 10 mug/ml for ibuprofen glucuronide and from 0.5 to 100 mug /ml for ibuprofen. The method is satisfactory for the analysis of ibup rofen and ibuprofen glucuronide from pharmacokinetic studies in humans . The direct determination of ibuprofen glucuronide allows accurate me asurement of this conjugate at low levels relative to the parent compo und, ibuprofen, a distinct advantage compared to previously employed i ndirect methods.