Pharmacokinetics of Acetylsalicylic Acid and Salicylic Acid After Intravenous Administration in Man

The pharmacokinetics of acetylsalicylic acid (ASA, 650 mg.) and salicylic acid (SA, 500 mg.) were studied following intravenous administration in males. The resultant plasma concentration-time curves were described by bi-exponential equations. The half-life of the first exponent was 2–5min. for both compounds while that of the second exponent was 13–19min. and 3.5–4.5hr. for ASA and SA, respectively. Over the dose range 0.3–1.2g. ASA, the area under the ASA plasma concentration-time curve was proportional to the dose administered. Also SA was shown to be the exclusive metabolite of ASA. Analysis of the present results, over the dose range and duration of study, showed that the data could best be fitted by conceiving the body to act as a two-compartmental open system with respect to these drugs. The significance of these findings on measurement of the rate constants of metabolism, volume of distribution, and other pharmacokinetic parameters are discussed.