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When the prostaglandin analogues were introduced a frequently asked question was would the use of an oral non-steroid anti-inflammatory drug (NSAID) blunt the effect of prostaglandin analogues on intraocular pressure (IOP)? Prostaglandins act directly on the prostanoid receptor, and NSAIDs exert their effect through inhibiting production/release of prostaglandins in the tissue, one would not expect an interaction between the two drugs. Thus, combining prostaglandin analogues and an oral NSAID has never been considered a problem. Still, in this issue of BJO , Chiba and co-workers (p 314 ) report that adding a topical NSAID (bromfenac) to eyes already treated with latanoprost induces a small increase in IOP, suggesting that NSAIDs after all blunt some of the effect of latanoprost on IOP. The authors do not suggest an interaction between the two drugs, but they put forward the idea that the explanation is that part of the effect of latanoprost on IOP is mediated by a release of naturally occurring prostaglandins. Thus, the effect on IOP of latanoprost, and presumably of the other PGF 2α analogues, should be a combination of two effects. One is a direct effect on the FP receptor mediated by the drug and not affected by NSAIDs. The other effect is the result of the release of naturally occurring prostaglandins presumably acting on some other prostanoid receptor. One could then expect that NSAIDs could abolish the latter part of the response. The authors conclude that the effect of NSAIDs is small and probably of little clinical significance, but that the results may provide information on the mechanism of action of latanoprost.
Obviously, the knowledge that prostaglandins have marked effects on IOP raised the question about a possible physiological role of endogenous prostaglandins in aqueous humour dynamics. They do not seem to be involved in the normal regulation of IOP. Levels of PGF 2α and PGE2 in aqueous are very low 1 and systemic administration of indomethacin or acetyl salicylic acid has no effect on IOP in normal or glaucomatous eyes. 2, 3 It is quite possible that the major role of endogenous prostaglandins is a pathophysiological one rather than a physiological one. In eyes with inflammatory changes in...