Abstract
Abstract: :
Purpose:To determine if the ocular hypotensive efficacy of ophthalmic drugs is affected by the time interval between application of each medication. Methods:Patients with elevated IOP chronically administering two topical ocular medications in the morning were enrolled and scheduled for 3 study visits. For each visit patients arrived prior to a.m. medication administration. Intraocular pressure (IOP) was measured by an examiner who was masked to the dosing interval. A different examiner timed the interval between the instillation of two different eye medications and administered the eye medications. A different dosing interval, 0min, 2min or 5min, randomly selected, was employed on each of the three study visits. The IOP was measured again two hours following administration of the second ocular medication. . Interval between visits was 2 to 14 days. The reduction in IOP in mmHg and the percentage reduction in IOP, compared to IOP prior to am dosing was calculated for each eye at each of the 3 time intervals. IOP reductions for different time intervals were compared using the two–tailed Student’s t–test. Results: 18 eyes from 6 male and 4 female patients were analyzed. Seven patients received Cosopt and Alphagan, two patients received Trusopt and Alphagan, and one patient received Cosopt and Iopidine. Nine patients were also on Xalatan and one patient was on Lumigan qhs. The mean ± SD IOP decrease was 3.29+ 1.90, 4.29 +3.37 and 4.94+ 2.92 mmHg (17.2%, 24.5% and 27.3%) for the 0min, 2min and 5min intervals respectively. The t–test revealed significant differences between the 0min and 2min (p=0.03) and between the 0min and 5min (p= 0.003) time intervals. However, the IOP reductions at the 2 min and 5min intervals were similar (p= 0.44). Conclusion:Allowing no time between successive eye medications is less effective in lowering IOP. Given the high cost of IOP lowering medications for many patients, and the demonstrated benefit of lower IOP in glaucoma patients, patients should be advised to wait at least 2 min between instilling eye drops to maximize their efficacy. A longer time interval may not improve effectiveness, while the inconvenience of a long wait may instead hinder patient compliance.
Keywords: pharmacology • drug toxicity/drug effects • clinical (human) or epidemiologic studies: health care delivery/economics/manpower