Corneal Pharmacokinetics of Meropenem

Abstract

 

Purpose

 

To evaluate the corneal pharmacokinetics of meropenem, a potentially novel antimicrobial in treating bacterial keratitis we quantify (1) the toxicity of meropenem compared to moxifloxacin on corneal cells in culture (2) the corneal penetration of meropenem across corneas mounted on artificial anterior chambers.

 

Methods

 

Human keratocyte cells (HKCs) and human corneal epithelial cells (HCE-Ts) in culture, were treated with either 5mg/ml or 2.5 mg/ml of meropenem or moxifloxacin for 1 hour. MTT cell viability assay was used to compare cell toxicity. Absorbance was read using an automated microplate reader and cell viability was expressed as percentages in relation to controls. Cell morphology of HKCs and HCE-Ts were assessed with fluorescent microscopy after incubation with meropenem compared to controls. Human cadaver corneas were used in corneal penetration experiments. Epithelium and endothelium were removed mechanically and corneas were mounted onto artificial anterior chambers. 10mg/ml of meropenem was inserted onto the corneas and samples of fluid in the artificial anterior chamber were removed at 45minutes, 1.5hrs, 3.5hrs and 24hrs. Meropenem concentrations were estimated from corneal homogenate and anterior chamber samples using; (1) disc diffusion bioassay measuring zones of inhibition when samples incubated with Escherichia Coli on agar plates and (2) reverse-phase High-Performance Liquid Chromatography (HPLC).

 

Results

 

MTT assays of HCE-T and HKC cells showed meropenem had significantly higher cell viability at both 5mg/ml and 2.5mg/ml compared to moxifloxacin p<0.05. Cell morphology of meropenem was indistinguishable from controls. Graph 1 summarises the diffusion of meropenem across 18 corneas. The mean corneal penetration of meropenem even at the earliest sampling point (45 minutes) were 4 times higher than the MIC90 seen with meropenem against keratitis isolates in a previous study. Concentrations of meropenem were seen to increase steadily throughout the sampling time period. Meropenem concentrations measured with bioassay were much higher than HPLC measurements.

 

Conclusions

 

We have previously shown meropenem to have excellent in vitro activity against both Gram positive and Gram negative isolates from patients with bacterial keratitis. This study suggests a good safety profile against corneal cells in culture. High corneal penetration of meropenem was seen at the earliest sampling point well in excess of the MIC90.

 

 

Keywords: 573 keratitis • 422 antibiotics/antifungals/antiparasitics • 480 cornea: basic science