In vitro transcorneal penetration of metronidazole and its potential use as adjunct therapy in Acanthamoeba keratitis

Cornea. 2004 May;23(4):386-9. doi: 10.1097/00003226-200405000-00014.


Purpose: To investigate the in vitro permeation of metronidazole through rabbit and human corneas in the presence and absence of 0.01% benzalkonium chloride and to suggest its use as adjunct therapy in the treatment of Acanthamoeba keratitis.

Methods: Metronidazole permeation through rabbit and human corneas, the latter being unsuitable for transplantation, were used for all permeability experiments. Flux rates for metronidazole from 0.5% and 1.0% aqueous solutions in the presence and absence of 0.01% benzalkonium chloride (BZCL) were determined. ANOVA and the Duncan multiple range test were used to test for steady state and an unpaired t test with the Welch correction was used to test for differences between the mean flux values at each time point. A significance level of 5% was used for all the statistical tests. In the clinical cases described, 0.5% aqueous solution was used.

Results: Steady-state flux rates for metronidazole from 0.5% and 1.0% solutions across both rabbit and human corneas were achieved after 6 and 4 hours, respectively. No statistically significant differences were obtained in the presence and absence of 0.01% BZCl (P < 0.05) between the steady state flux values at both concentrations of metronidazole of human and rabbit corneas, except for 0.5% metronidazole across rabbit corneas. Flux rates of metronidazole across human corneas were 12%-33% higher than those across rabbit corneas. For both rabbit and human corneas, flux rates of metronidazole from 0.5% and 1.0% solutions were reduced by between 4% and 11%, respectively, in the presence of 0.01% benzalkonium chloride.

Conclusions: Although statistically significant differences in flux values were obtained between human and rabbit corneas, the study supports the suitability of the in vitro rabbit cornea as a model for investigating permeation of drugs through human corneas. However, direct extrapolation of animal data to humans must be approached cautiously. The metronidazole from a 1% solution had a steady-state flux rate approximately double that from the 0.5% solution. Higher concentrations of up to 1% may be considered for clinical use for treating Acanthamoeba keratitis infections. It would appear to be prudent to omit benzalkonium chloride as a preservative from preparations of metronidazole formulated for topical ophthalmologic use. Early clinical experience with the topical solution as adjunct therapy in the treatment of Acanthamoeba keratitis is encouraging.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Acanthamoeba Keratitis / drug therapy*
  • Adult
  • Aged
  • Animals
  • Anti-Infective Agents / pharmacokinetics*
  • Anti-Infective Agents / therapeutic use*
  • Benzalkonium Compounds / pharmacokinetics
  • Chemotherapy, Adjuvant
  • Chromatography, High Pressure Liquid
  • Cornea / metabolism*
  • Humans
  • Metronidazole / pharmacokinetics*
  • Metronidazole / therapeutic use*
  • Middle Aged
  • Ophthalmic Solutions
  • Permeability
  • Preservatives, Pharmaceutical / pharmacokinetics
  • Rabbits


  • Anti-Infective Agents
  • Benzalkonium Compounds
  • Ophthalmic Solutions
  • Preservatives, Pharmaceutical
  • Metronidazole