Concentrations of metronidazole in human plasma and saliva after tablet or gel administration

Objectives The aim of this study was to determine the pharmacokinetic profile of metronidazole (Mtz) tablet and to compare Mtz gel and tablet concentrations in both blood plasma and saliva. Methods In this randomized cross-over study with a 1-week washout period, 13 volunteers randomly received one (a single oral dose of 750 mg Mtz (Flagyl® - tablet) and 2) 3 g of 15% Mtz benzoate gel (applied by using a dental tray). The HPLC with ultraviolet detection was used to quantify plasma and saliva concentrations of Mtz. The pharmacokinetic parameters (PPs) areas under the curves from 0 to 48 h (AUC _0-48) and from 0 to infinity (AUC_0-∞), the maximum plasma concentration (C_max), the time to C_max, volume of distribution and renal clearance were determined for Mtz tablet. Key findings Considering the Mtz tablet, plasma showed higher Mtz concentration from 6 to 24 h after drug administration and the highest values concerning AUC _0-48h and AUC_0-∞ than those obtained in saliva (P < 0.05). No significant differences were observed between plasma and saliva concentrations for Mtz gel. Conclusions The study showed that some PPs were higher in plasma (P < 0.05) than in saliva concerning Mtz tablet. Gel formulation had similar Mtz bioavailability in plasma and saliva resulting in systemic absorption.