DETERMINATION OF ACETYLSALICYLIC-ACID AND SALICYLIC-ACID IN SKIN AND PLASMA BY HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHY

This study describes a HPLC method to determine the concentrations of acetylsalicylic acid (ASA) and salicylic acid (SA) in human stratum co rneum and in plasma. The stratum corneum layers for ASA/SA analysis we re removed from three patients with postherpetic hyperalgesia treated with topical and oral aspirin. Blood samples were also collected from the same patients. Tape strippings were placed in acetonitrile and son icated for 15 min. After centrifuging, aliquots of the supernatant wer e injected into the chromatograph. ASA and SA from plasma samples were extracted on Isolute C-8 columns. Due to interfering peaks in the tap e samples, HPLC conditions were slightly different for tape and plasma samples. ASA and SA were separated on a LiChrospher 100 RP-18 column at 1 ml/min using a water-phosphate buffer (pH 2.5)-acetonitrile mobil e phase (35:40:25, v/v/v). A linear response to quantities of ASA from 0.1 to 100 mu g/cm(2) and of SA from 0.1 to 5 mu g/cm(2) in tape and to quantities of ASA 0.1 to 2 mu g/ml and 1 to 50 mu g/ml was obtained and the recovery from tape and plasma samples was over 98%. The metho d is sensitive (C.l mu g/cm(2)) and specific enough to allow the deter mination of the drugs in the skin not only after topical but also afte r oral administration. A good sensitivity was also obtained in plasma (0.1 mu g/ml) allowing study of the kinetics of ASA and SA in plasma a fter oral administration. Concentrations of ASA after topical administ ration were 100-200 times higher than after oral administration. Plasm a levels of ASA and SA after oral administration were similar to those previously found. No ASA or SA were detected in plasma after topical ASA administration. (C) 1998 Elsevier Science B.V.