MONITORING OF COTRIMOXAZOLE CONCENTRATIONS IN SERUM DURING TREATMENT OF PNEUMOCYSTIS-CARINII PNEUMONIA

The purpose of this prospective randomized open trial was to investiga te the impact of monitoring concentrations in;serum on the efficacy an d side effects of high-dose co-trimoxazole therapy, Forty consecutive patients with microscopically confirmed Pneumocystis carinii pneumonia were enrolled, Therapy was started with 5 and 25 mg bf trimethoprim a nd sulfamethoxazole, respectively, per kg of body weight given every 6 h for 2 days and continued every 8 h either with (group A) or without (group B) monitoring and dose adjustments according to sulfamethoxazo le levels in serum (target, 150 to 200 mu g/ml) for a total of 21 days , Only 7 of 19 (group A) and 11 of 21 (group B) patients tolerated a f ull S-week course, Adverse effects were observed in 33 patients (83%). Patients who mere treated for the full period and patients for whom c o-trimoxazole was prematurely stopped had similar concentrations of su lfamethoxazole (157 +/- 52 versus 155 +/- 47 mu g/ml) and trimethoprim (5.0 +/- 1.4 versus 5.6 +/- 1.9 mu g/ml). Concentrations of sulfameth oxazole and trimethoprim in group A (158 +/- 39 and 5.6 +/- 1.8 mu g/m l, respectively) did not differ from those in group B (153 +/- 57 and 5.1 +/- 1.6 mu g/ml, respectively), and the average daily maintenance doses for groups A (75.4 mg/kg plus 15.1 mg/kg) and B (76.4 mg/kg plus 15.3 mg/kg) were nearly identical, Although the average sulfamethoxaz ole concentrations were maintained within the target zone in the monit oring group (day 5, 160 +/- 44 mu g/ml; day 10, 160 +/- 41 mu g/ml; da y 15, 168 +/- 61 mu g/ml; and day 21, 157 +/- 95 mu g/ml), only 28% of the individual sulfamethoxazole levels were within the target range o f 150 to 200 mu g/ml after the dose adjustments (32% in group B withou t intervention), Response rates were similar in both groups, Complete response or improvement was observed in 18 of 19 (group A) and 19;of 2 1 (group B) patients, The method used for monitoring sulfamethoxazole levels with subsequent dose adjustment did not allow us to reliably ac hieve the target concentrations and did not significantly alter the in cidence of side effects or the efficacy of the therapy.