Carbonic anhydrase inhibitors as fourth drug in primary glaucomas: Is it worth it?

Objective: To evaluate the effectiveness of carbonic anhydrase inhibitors as the fourth drug regarding intraocular pressure (IOP) control in patients with primary glaucomas. Design: Single-centre, prospective study. Participants: Twenty-five eyes from 25 patients with primary glaucomas treated concomitantly with a topical prostaglandin analogue, a beta-blocker, an a-adrenergic agonist, and a carbonic anhydrase inhibitor. Methods: Patients followed at the Federal University of Sao Paulo were enrolled from August to November 2013 and were initially submitted to an ophthalmologic examination where the IOP was measured at 8 AM, 10 AM, and 12 PM. Afterward, patients underwent a 15-day washout of the carbonic anhydrase inhibitor and had their IOP measured again. Results: Most patients were female, white, and with a mean age of 66.4 +/- 9.7 years. The removal of the fourth drug had a statistically significant effect on the IOP peak (increase of 1.20 mm Hg, p < 0.01) and mean (increase of 1.23 mm Hg, p < 0.01), but it did not interfere significantly with morning fluctuation of the IOP (p = 0.83). After discontinuation of the fourth drug, the IOP increased >= 2 mm Hg in 32% of the patients, and there was a significant increase of the IOP (defined as an IOP change >= 20%) in only 5 patients (20%). Age older than 60 years was associated with 20% of the documented IOP change (R-2 = 0.19, p = 0.03). Conclusions: The removal of a fourth medication does not appear to have a clinically significant impact on IOP control in most patients with glaucoma. However, 32% of the patients experienced an IOP increase >= 2 mm Hg, with age older than 60 years being the only significant predictive factor.