A High-throughput Spectroscopic-based Bioassay Method for Determination of Fosmidomycin in Plasma: Application for Pharmacokinetic Study

Abstract

A simple, sensitive, selective and reproducible bioassay based on spectroscopic
method was developed for the determination of fosmidomycin in human plasma.
Enterobacter cloacae ATCC 23355 strain was used as a test organism. Inhibition of bacterial
growth was assessed using MTT assay. Calibration curves were prepared from concentration
response curves in plasma (0, 0.5, 1, 2.5, 5, 12.5, 25, 50 ng/μl) and were all linear with
correlation coefficients better than 0.995. The precision of the method based on within-day
repeatability and reproducibility (day-to-day variation) was below 10% (% coefficient of
variations: % C.V.) Good accuracy was observed for both the intra-day and inter-day assays,
as indicated by the minimal deviation of mean values found between the measured samples
and the theoretical values (below +10%). Limit of quantification (L.O.Q.) was accepted as
0.5 ng using 20 μl plasma or 10 μl urine sample. The mean recovery for fosmidomycin was
greater than 99%. The method was free from interference from other commonly used
antibiotics including azithromycin. The method appears to be robust and has been applied to
a pharmacokinetic study to determine the plasma of fosmidomycin in a Thai patient with
acute uncomplicated falciparum malaria following oral doses of 1,800 mg fosmidomycin
given every twelve hours for three days, in combination with azithromycin at the dose of 750
mg given every twelve hours for three days.