Effect of drug vehicle on human ocular retention of topically applied tetracycline.

Tetracycline hydrochloride--as a 1% suspension in oil, 1 and 2% suspension in ointment, and 1 and 2% solution in water or balanced salt solution USP--was applied once to the conjunctival cul-de-sacs of volunteers and patients before cataract extraction. The tear film concentrations of drug were maintained above a bacteriostatic level in excess of six hours for 1 and 2% tetracycline in ointment, less than two hours for 1% tetracycline in oil, and less than 30 minutes for 1 and 2% tetracycline in water or balanced salt solution. The 2% tetracycline in ointment produced the highest tear film levels of drug. The 1% tetracycline in oil induced excessive lacrimation and much of the drug was washed from the conjunctival surface. The tear film levels of the drug were mirrored by the maintenance of bacteriostatic levels of tetracycline in the aqueous humor for 1 1/2 hours with 2% tetracycline in ointment. Whereas 1% tetracycline in ointment produced drug levels approaching bacteriostasis in the aqueous humor, 1% tetracycline in oil produced only trace levels of the drug within the anterior chamber. The ointment acted as a depot for the suspended drug and most of the drug in the absence of excessive tearing was lost from the conjunctiva via the lacrimal system.