The lack of efficacy of topical beta-blockers, timolol and betaxolol on intraocular pressure in Nigerian healthy volunteers

The beta-adrenoceptor antagonists are commonly used drugs in ophthalmic and medical practice. While beta-blockers may show reduced antihypertensive efficacy in African patients, the effect of beta-blockers on intraocular pressure (IOP) in African healthy volunteers is less well known. This single-masked, placebo-controlled, randomised study was conducted to investigate the response of healthy Nigerian volunteers to a single drop of the beta-adrenoceptor antagonists timolol and betaxolol. Twenty-five volunteers participated in the study; however, only 19 were able to complete the study. The concentrations of the beta-blocker used were 0.0625%, 0.125%, 0.25% and 0.5%. One eye of the volunteers was used while the other eye served as control. The baseline IOP was documented and IOP measured hourly over 6 h. Pupillary size, corneal sensitivity and visual acuity were also assessed. Cardiovascular parameters were also documented hourly (blood pressure, heart rate, pulse rate). Only 0.5% concentrations of both beta-adrenoceptor antagonists caused any significant IOP reduction in normal volunteers (p < 0.05). The maximal falls were -2.33 +/- 2.2 mmHg and -1.23 +/- 0.6 mmHg with timolol and betaxolol, respectively. The IOP reduction produced lasted for only 4 h, after which the IOP returned to baseline. There was also an overshoot of the IOP above the baseline values in all the volunteers (+2.0 to +2.3 mmHg). There was no significant change in the cardiovascular parameters. There was no effect on the pupillary size, visual acuity or corneal sensitivity. There was no significant change in IOP and cardiovascular parameters in the placebo group. Both beta-adrenoceptor antagonists caused an attenuated IOP reduction in African normal volunteers, compared with values reported in Caucasians. There was a rebound intraocular hypertensive effect demonstrated with both beta-adrenergic antagonists in blacks.