Ocular penetration of topically applied linezolid in a rabbit model

Abstract

Purpose: To evaluate ocular penetration of topically applied linezolid, a new antibiotic agent targeted against gram-positive organisms.

Setting: Laboratory of Pharmacology, University Hospital of Strasbourg, Strasbourg, France.

Methods: New Zealand White rabbits were divided into 3 equal groups. One drop of 50 microL (2 mg/mL) linezolid was administrated in Group 1. In Group 2, eyes were dosed in accordance with a keratitis protocol (1 drop of 2 mg/mL every 15 minutes for 1 hour). Aqueous humor was sampled 6 times from immediately after to 3 hours after drop delivery. In Group 3, a keratitis protocol was implemented before the animals were humanely killed. Conjunctiva, cornea, vitreous, and blood samples were collected 1 hour and 2 hours after the last drop. Linezolid concentrations were measured by high-performance liquid chromatography.

Results: Each group comprised 8 rabbits. In Group 1 and Group 2, the peak linezolid concentration in the aqueous humor (mean 0.87 mg/L +/- 0.16 [SD] and 2.17 +/- 0.4 mg/L, respectively) was 45 minutes after the last drop delivery. In Group 3, the concentrations 1 hour and 2 hours after the last drop were higher than 3 microg/g in the conjunctiva samples and higher than 4 microg/g in the cornea samples. The linezolid concentration in the vitreous and serum was negligible.

Conclusions: Linezolid levels in the aqueous humor, conjunctiva, and cornea exceeded the minimum inhibitory concentration of most gram-positive organisms that cause bacterial keratitis and endophthalmitis. Linezolid could be a valuable alternative in cases of increased resistance to vancomycin.