A liquid chromatography assay for the study of serum and gastric juice metronidazole concentrations in the treatment of Helicobacter pylori.

Metronidazole is an important component of combination antimicrobial therapies used in the eradication of Helicobacter pylori, a recognized cause of gastritis and duodenal ulcer. Studies are needed to understand which pharmacokinetic factors determine the success of metronidazole therapy and what role drug monitoring plays. Such studies require a rapid, accurate assay for small volumes of sample, including gastric juice, over a 200-fold range of concentrations. Using an isocratic high-performance liquid chromatography (HPLC) method, with an 8-min run time and protein precipitation of samples, metronidazole could be measured reliably to as low as 0.5 mg/L in 100 microliters samples of serum, gastric juice, or saliva. Standard curves for serum and gastric juice were linear between 0.5 and 50 mg/L. Within-day coefficients of variation (CVs) (n = 5 at six concentrations) ranged from 1.1 to 4.8% over this range and the between-day CV (n = 7 days) was 5.8%. Neither omeprazole nor common gastroenteric and cardiac medications interfered with this assay. A pilot study, done in four healthy volunteers given intravenous metronidazole 500 mg before and after 7 days of omeprazole therapy, found metronidazole to be present in higher concentrations in gastric juice and saliva than in serum 2 h after intravenous administration. The range and accuracy of the assay proved to be suitable for carrying out pharmacokinetic studies at clinically used doses of the drug.