Discrepancy in plasma melarsoprol concentrations between HPLC and bioassaymethods in patients with T gambiense sleeping sickness indicates that melarsoprol is metabolized

OBJECTIVE With the use of a specific high-performance liquid chromatography (HPLC) method and a bioassay which determines trypanocidal activity concen trations of melarsoprol were assessed in plasma, urine and cerebrospinal fl uid (CSF) from 8 patients with late-stage Trypanosoma gambiense sleeping si ckness. The aim was to unravel to what extent the bioassay codetermines bio logically active metabolites of melarsoprol. METHODS Subjects were given on e dose of melarsoprol i.v. per day for 4 days (1.2, 2.4, 3.0-36, 3.0-3.6 mg per kg b.w. respectively). Plasma samples were obtained before the first m elarsoprol injection, immediately after and at 1 h, 24 h and 5 days after t he 4th injection. Urine was collected before melarsoprol therapy and at 24 h after the 4th injection. CSF samples were taken once before treatment and at 24 h after the 4th injection. RESULTS HPLC analyses showed that plasma concentrations immediately after the 4th injection varied from 2200 to 15 9 00 nmol/l; dropping to 0-1800 nmol/l at 1 h; and to undetectable levels at 24 h. In urine small amounts of melarsoprol were recovered. Melarsoprol cou ld not be detected in CSF by HPLC. Immediately after injection, bioassay an alyses showed plasma concentrations of the same magnitude as HPLC assays bu t at 1 h they were 4-65-fold higher than the levels assessed by HPLC. Even 24h and 5 days after the 4th injection there was significant but decreasing activity. Urine levels were 40-260-fold higher than the measured HPLC conc entrations, whereas there was low but detectable activity in CSF CONCLUSION Results indicate that melarsoprol is rapidly eliminated from pla sma. The significant trypanocidal activity determined by bioassay and simul taneuos low or undetectable levels of melarsoprol assayed by HPLC indicate that the compound is transformed into metabolites with parasiticidal activi ty.