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Treatment or Prevention of Herpes Simplex Virus Retinitis with Intravitreally Injectable Crystalline 1-O-Hexadecylpropanediol-3-Phospho-Ganciclovir

¹ From the Shiley Eye Center, University of California San Diego, La Jolla, California; and the ² Department of Medicine, Veterans Affairs Medical Center, and University of California San Diego, La Jolla, California.

PURPOSE. To evaluate an intraocular drug delivery system consisting of the crystalline ammonium salt of 1-O-hexadecylpropanediol-3-phospho-ganciclovir (HDP-P-GCV) as a slow-release form of the drug.

METHODS. A dosage of 0.885, 1.57, 2.8, 4.486, or 8.85 µmol of ammonium salt HDP-P-GCV in 0.1 mL was intravitreally injected into rabbit vitreous. The toxicity and safety were evaluated with ophthalmoscopy, electroretinography, and pathology. Drug vitreous levels were determined at various time intervals by means of HPLC. The treatment efficacy and duration of efficacy were tested in a herpes simplex virus (HSV)-1 retinitis rabbit model.

RESULTS. Intravitreal injections of the compound revealed clear vitreous of optic axis, a desirable drug depot in the inferior vitreous cavity, and no clinical toxicity, except for variable mild local posterior subcapsular cataract and local retinal toxicity with high doses. HPLC analysis showed free ammonium salt of HDP-P-GCV in the upper vitreous at a level of 0.2 µM 12 weeks after the 2.8-µmol initial intravitreal dose. Drug concentration was still 1.95 µM 20 weeks after the 8.85-µmol initial intravitreal dose. These concentrations (0.2 and 1.95 µM) were 10 and 100 times higher, respectively, than the median inhibitory concentration (IC₅₀) of HSV-1 (0.023 µM). Treatment with the highest nontoxic dose (2.8 µmol) and the highest dose (8.85 µmol) showed significant protection from HSV-1 infection (P < 0.05) and provided sustained antiviral effect after a single intravitreal drug injection.

CONCLUSIONS. The crystalline ammonium salt of HDP-P-GCV may be a very useful local therapy for herpes family viral retinitis.

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