A highly sensitive HPLC method for the simultaneous determination of acetylsalicylic, salicylic and salicyluric acids in biologic fluids: pharmacokinetic, metabolic and monitoring implications.

A number of methods have been developed for the determination of acetylsalicylic acid (ASA, aspirin). However, they are not sensitive enough for the simultaneous determination of ASA and its major metabolites salicylic (SA) and salicyluric (SUA) acids at the low dosage schedules (30-100 mg ASA/d). The HPLC method with UV detection described here fulfills these requirements. The calibration curves were linear at the range 0.18-10 mumol/l. Coefficients of variation were 3.9% for SUA, 7.89% for ASA and 5.88% for SA. The recovery of ASA, SA and SUA was between 90-105%. ASA administered in doses of 30-400 mg was rapidly absorbed from gastrointestinal tract and deacetylated, forming the dominant plasma metabolite SA. SA was eliminated to about 60% by conjugation with glycine and therefore SUA was a dominant metabolite in urine. ASA was never found in urine at the low-dose ASA treatment. For this reason, SUA, but not ASA, can be determined in urine and may be used for monitoring patient compliance.