LATANOPROST TWICE-DAILY IS LESS EFFECTIVE THAN ONCE-DAILY - INDICATION OF RECEPTOR SUBSENSITIVITY

Purpose. It is known that twice daily dosing of latanoprost is less ef fective in reducing intraocular pressure (IOP) than once daily applica tions. The aim of the present study was to investigate this phenomenon further in order to see if the results could be compatible with a sub sensitivity of the FP-receptor. Methods. Latanoprost, 50 mu g/ml, was instilled once daily (8 PM) in one eye of 40 healthy volunteers and tw ice daily (8 AM and 8 PM) in the fellow eye in a randomized, masked fa shion for 2 weeks, with the last drop on the evening of Day 15. IOP wa s determined at 8 AM, noon and 4 PM on Days 0, 2, 15 and 16. Also, the effect of a single dose of latanoprost was measured 6-11 months after cessation of treatment. Results. There was a significant reduction of mean diurnal IOP from Day 2 (p < 0.001), with both dose regimens. Onc e-daily dosing resulted in a significantly lower IOP compared with twi ce-daily dosing on Day 15 (p < 0.001) but not on Day 2. The difference remained (p < 0.001) on Day 16 when no morning dose had been given, b ut was not present after a single application 6-11 months later. Concl usions. The results of the present study are compatible with developme nt of subsensitivity, at the level of the FP-receptor or its associate d intracellular signaling pathways, with twice-but not with once-daily dosing of latanoprost. This effect is reversible.