Drug interaction in the eye. Concurrent corticosteroid-antibiotic therapy for inflammatory keratitis.

Concurrent instillation of individual preparations of a corticosteroid and an antibiotic resulted in significantly (P less than .05) lower peak corneal and aqueous humor steroid levels than those achieved by the steroid alone. Both the interval elapsing between instillation of the two drugs and the sequence in which they were administered influenced subsequent steroid bioavailability. Corticosteroid levels in the cornea after administration of a combination steroid-antibiotic preparation were not significantly different (P less than .05) from those detected after instillation of the same steroid alone, suggesting that, for the treatment of corneal disorders, use of a combination preparation may offer a method to circumvent certain drug interactions. The decrease in ocular steroid bioavailability could not be directly equated with differences in antinflammatory effectiveness, so that the therapeutic relevance of the demonstrated drug interaction is not known.