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Editors Selection IGR 7-1

Medical treatment: Prostaglandins

Comment by Richard Parrish II on:

11738 Effects of the combination of bimatoprost and latanoprost on intraocular pressure in primary open angle glaucoma: a randomised clinical trial, Doi LM; Melo LA Jr; Prata JA Jr, British Journal of Ophthalmology, 2005; 89: 547-549

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Doi et al. (623) have demonstrated that 'more is less' for the intraocular pressure (IOP) lowering effects of additional topical hypotensive lipids or prostaglandin analogs. In a well powered randomized clinical trial the addition of topical bimatoprost to latanoprost significantly raises, rather than lowers IOP. The discontinuation of bimatoprost in Phase 2 of this two part study resulted in a return to the lower baseline IOP. This is not too surprising in view of previous FDA Phase 3 studies of three different prostaglandin analogs, bimatoprost, travaprost, and latanoprost that established once daily dosing yielded the best therapeutic index for all three potent topical medications. Given that these three medications with relatively high affinities for the FP receptor achieve IOP lowering by receptor stimulation; it

Latanoprost and bimatoprost should not be used together

seems unlikely that a higher drug concentration would have produced a substantially greater IOP lowering effect. In the second part of the study, control eyes that received latanoprost were switched from latanoprost to bimatoprost. This switch failed to demonstrate a statistically significant difference in IOP lowering between the two topical treatments. In view of previously published studies this is also not unexpected. The authors conclude: "The reason for the IOP increase with the adjunctive use of both medications could not be clarified in our study." Despite not having demonstrated a precise mechanism of why the co-administration of these two individually potent drugs should result in an elevated IOP, the message that latanoprost and bimatoprost should not be used together is still compelling.

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