Plasma Levels of Aspirin Metabolites in Libyan Patients with Rheumatoid Arthritis and Rheumatic Fever

Plasma aspirin metabolite levels were studied in Libyan adult patients with rheumatoid arthritis (RA) (Number: 4, age: 37-50 years, sex: 2 males, 2 females) and in pediatric patients with rheumatic fever (RF) (Number: 6, age: 5-12 years, sex: 3 males, 3 females) given high doses of aspirin. Two hours after the daily dose of aspirin therapy, plasma salicylic acid (SA), salicyluric acid (SU) and gentisic (GA) were analyzed by high performance liquid chromatography system. In adult patients with RA, plasma levels of GA varied from 1.2 mg/L on day 1 to 2.7 mg/L on day 7, while SU levels varied from 4.9 mg/L on day 1 to 10.2 mg/L on day 7 and SA varied from 60.2 mg/L on day 1 to 305 mg/L on day 7. All adult patients with RA reached steady state for SA between 5th and 6th day of high aspirin doses. In pediatric patients with RF, plasma SA level varied from 130.2 mg/L to 610 mg/L, while SU level varied from 1.8 mg/L to 17.5 mg/L. Some pediatric patients showed very low levels of plasma GA, while others exhibited plasma GA levels as high as 4.1 mg/L. The females, in both groups of patients, had higher plasma SA levels than males. The female children with RF had higher GA levels than adult patients with RA (3.9±0.1 vs 2.6±0.08 t=12.7, df = 5, p<0.01). Thus this study had shown that there is a wide variation in the pharmacokinetics of aspirin metabolism. It is therefore suggested that plasma aspirin metabolite levels of patients on long term high dose salicylate therapy be monitored routinely to ascertain if therapeutic, rather than toxic, plasma levels are reached and being maintained.