Pharmacokinetics of metronidazole in saliva

Measurement of metronidazole concentration and its pharmacokinetics from saliva and serum samples have been conducted in 8 healthy volunteers. The pharmacokinetic study was carried out after an oral ingestion of 500 mg tablet of the drug, simultaneously from saliva and serum samples. The study showed a significant positive correlation between saliva and serum metronidazole concentrations. However, a better correlation was obtained during the elimination phase (r = 0.90, n = 51, p less than 0.001) compared to that during the absorption phase (r = 0.76, n = 26, p less than 0.001). The overall ratio of saliva to serum concentration was 0.93 +/- (SEM 0.05). Not surprisingly, the half-life of metronidazole obtained from saliva samples (8.03 +/- SEM 0.59 hours) was similar to that from serum (7.97 +/- SEM 0.39 hours). The mean area under the drug concentration (AUC0-infinity) in saliva was 153.56 +/- (SEM 16.42 micrograms/ml hour) and that in serum was 179.76 +/- (SEM 11.70 micrograms/ml hour), yielding a saliva to serum ratio of 0.87 (+/- SEM 0.10). It could be concluded, therefore, that the measurement of metronidazole concentration from saliva can be used for the estimation of its pharmacokinetics and may also be used as reliable and convenient method for bioequivalence studies.