Plasma Concentrations of Oral Metronidazole in the Early Post-Laparotomy Periods

Background: The bioavailability of metronidazole after oral ingestion, in ordinary conditions, is quite similar to intravenous administration of the drug.  However, the degree of its absorption is not known in the early periods after laparotomy. Objective:  To determine plasma levels of metronidazole in pediatric patients following elective abdominal surgery. Methods: The study group was comprised of 25 pediatric patients with mean age of 8.25 years.  They took 10 mg/kg metronidazole (ingested or taken via nasogastric tube) a few hours after operation, followed by every eight hours for a total of three successive doses.  We obtained blood samples 1-2 hours after each drug intake. Results: The mean±SD of plasma drug concentrations after the first, second and third doses were 1.43±0.81, 6.26±3.86 and 10.21±4.28 mg/ml, respectively, showing a significant rise after each dose (p<0.001).  The majority of patients (84%) obtained a level equal to, or above the minimal bactericidal concentration (MBC) after the third dose.  Ninety-two and 96% of patients achieved the plasma minimal inhibitory concentration or higher following the second and third doses, respectively, as compared to 4% after the first dose (p<0.00001).  Conclusion:  Absorption of oral metronidazole after elective laparotomy is disturbed only temporarily, as in the majority of patients the drug attains an acceptable level before the second post-operative day.  Therefore, parenteral metronidazole therapy, if necessary, is recommended only during the first 24 hours, and it may be replaced by oral preparation afterward.