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

To evaluate the effectiveness of carbonic anhydrase inhibitors as the fourth drug regarding intraocular pressure (IOP) control in patients with primary glaucomas.

Single-centre, prospective study.

Twenty-five eyes from 25 patients with primary glaucomas treated concomitantly with a topical prostaglandin analogue, a β-blocker, an α-adrenergic agonist, and a carbonic anhydrase inhibitor.

Patients followed at the Federal University of São 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.

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).

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.