Comparison of IOP Response to Timolol Versus Latanoprost

Abstract

Purpose : Prostaglandin analogues and beta-blockers are effective intraocular pressure (IOP) lowering drugs commonly used for glaucoma. However, there remain a sizeable number of nonresponders to these treatments. This study used both iCare and pneumatonometry to identify the IOP response to latanoprost and timolol under monotherapy.

Methods : We examined 212 eyes from 106 ocular normotensive, non-glaucomatous volunteers (76% female, 55.5 ± 8.9 years of age) from the EDEN consortium. At baseline, IOP was measured by iCare at 9AM and 11AM, and pneumatonometry at 11AM. Subjects were randomized and treated in both eyes (OU) with either 0.005% latanoprost once daily or 0.5% timolol twice daily for 7 days, with measurements repeated on day 8 of each treatment. After a 6-week washout, subjects switched drug arms. IOP-responders were those having an IOP reduction of >15% OU, while mixed responders had an IOP reduction of >15% in one eye (OD or OS). Treatment effects and intereye correlations on IOP were analyzed using Spearman’s rho, two-tailed paired t-tests and Fisher’s Exact Test.

Results : As compared to baseline, timolol and latanoprost effectively lowered IOP by 13% OD (14% OS) and 17% OD (18% OS), respectively (p < 0.0001, pneumatonometry). Twenty-two subjects (21%) failed to respond to either latanoprost or timolol OU. IOP response to timolol did not predict IOP response to latanoprost, however, latanoprost responders tended to also respond to timolol. More subjects were IOP-responders OU when taking latanoprost compared to timolol (p < 0.007), with 54% responding to latanoprost and 28% responding to timolol (pneumatonometry) (Figure 1). In patients given timolol, a higher non-response rate was found when measuring with pneumatonometry as opposed to iCare (p = 0.037) (Figure 1).

Conclusions : In this group of healthy subjects, a significant amount did not respond to either timolol or latanoprost. Even though the drugs represent two different mechanisms of action (timolol decreasing aqueous flow and latanoprost increasing uveoscleral outflow), non-response to one drug did not predict response to another. A new study is underway to determine if this pattern persists in patients with ocular hypertension.

This is a 2021 ARVO Annual Meeting abstract.

 

Figure 1. IOP response rates of latanoprost and timolol with iCare and Pneumatonometry. Responder, >15% decrease in IOP OU; Non-responder, <15% decrease in IOP OU; Mixed Responder, >15% decrease in IOP in one eye, OD or OS. * indicates p < 0.05.