Intraocular concentrations of Clindamycin obtained by sequential parabulbar injections

Purpose: To measure the intraocular concentration of Clindamycin that can be maintained by sequential injection through a retained parabulbar catheter. Materials and Methods: The peak intraocular concentration and half- life of Clindamycin after parabulbar injection was determined in a rabbit model. In a second experiment a parabulbar catheter was inserted and the maximum concentration that could be maintained by sequential injection through the catheter at intervals of 6 hours was determined. In a third experiment both eyes of the rabbit were catheterized and one infused with Clindamycin. The eyes were enucleated and studied by light and electron microscopy for changes induced by Clindamycin and the catheter. Results: The concentration of Clindamycin after a single parabulbar injection of 10 mg/kg peaked in the retina and choroid at 2 hours and was 336 μg/g. The serum level at 2 hours was 2.2 μg/ml. The half-life in choroid and retina was 1 hour. Sequential administration at 6 hour intervals maintained a minimum concentration of 87 μg/ml. The vitreous concentration was maintained at 2 μg/ml. Conclusion: The level of Clindamycin in the retina and choroid obtained by sequential injections of 10 mg/kg exceeds the minimum lethal dose for organisms susceptible to the drug. The low serum concentration suggests that sequential doses of Clindamycin by the parabulbar route might be an effective therapy for toxoplasmic retinochoroiditis and would diminish the risk of colitis or other deleterious systemic side effects.