To the Editor.—In an article entitled "Drug Interaction in the Eye: Concurrent Corticosteroid-Antibiotic Therapy for Inflammatory Keratitis" (Arch Ophthalmol 95:682-685, 1977) Leibowitz and Kupferman studied the concurrent and sequential administration of topical antibiotic and corticosteroid to the rabbit eye. Although variation of sequence and intervals between drug instillation produced somewhat erratic results, the authors demonstrated that the tissue concentration of steroid in the cornea was reduced to a greater extent following the sequential instillation of the individual drugs in either order than was the concentration following the administration of an antibiotic-steroid combination. The authors conclude that for certain corneal disorders, use of a combination preparation may increase steroid bioavailability. In addition, these authors point out that the human cul-de-sac can retain only a small portion of two average drops, which is, to these authors, another advantage of combination formulations.
In one set of experiments, Leibowitz and Kupferman administered the
Baum JL, Barza M. Washout Effect vs Drug Interaction. Arch Ophthalmol. 1977;95(12):2229. doi:10.1001/archopht.1977.04450120135020