Cotrimoxazole plasma levels, dialyzer clearance and total removal by extended dialysis in a patient with acute kidney injury: risk of under-dosing using current dosing recommendations

BACKGROUND: Dosing of antibiotics in critically ill patients is challenging. It becomes even more difficult if renal or hepatic impairment ensue. Modern means of renal replacement therapy are capable of removing antibiotics to a higher rate than decades ago, leaving clinicians with a high degree of uncertainty concerning the dose of antibiotics in this patient population. Cotrimoxazole, a combination of trimethoprim (TMP) and sulfamethoxazole (SMX) is frequently used in the treatment of several infections including Pneumocystis jirovecii pneumonia (PCP). CASE PRESENTATION: Here we describe a patient with acute kidney injury in which we investigated the TMP and SMX levels during the course of an ICU stay. Cotrimoxazole was administered every six hours i.v. in a dose of TMP/SMX 15/75 mg/kg/day. Extended dialysis was performed with a high-flux dialyzer. Blood samples, as well as pre- and postdialyzer samples and aliquots of the collected spent dialysate were collected. Observed peak concentrations (Cmax) were 7.51 mg/l for TMP and 80.80 mg/l for SMX. Decline of blood levels during extended dialysis (TMP 64%; SMX 84%) was mainly due to removal by the dialysis procedure, illustrated by the high dialyzer clearances (median of 4 extended dialysis sessions: TMP 94.0 / SMX 51.0 ml/min), as well as by the absolute amount of both substances in the collected spent dialysate (median of 6 extended dialysis sessions: TMP 556 mg / SMX 130 mg). Within the limitation of a case report our data from 4 consecutive extended dialysis sessions suggest that this procedure substantially removes both TMP and SMX. CONCLUSIONS: Dose reduction, which is usually advocated in patients with acute kidney injury under renal replacement therapy, might lead to significant under-dosing. Pharmacokinetic studies for TMP/SMX dosing in this patient population are necessary to allow adequate dosing.