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Editors Selection IGR 16-1
Medical Treatment: Real-life effectiveness and clinical trial efficacy of anti-glaucoma drugs
Comment by Ramanjit Sihota on:
56218 Effectiveness of intraocular pressure-lowering medication determined by washout, Jampel HD; Chon BH; Stamper R et al., JAMA ophthalmology, 2014; 132: 390-395
See also comment(s) by Robert Feldman •This is an interesting but retrospective study purportedly looking at a possible 'real-world' scenario of medical therapy in glaucoma. Data of 619 patients having mild or moderate primary open-angle glaucoma, being screened for inclusion in a phase-3 study of CyPass Micro-Stent was analyzed. Patients underwent a screening IOP measurement at one point in time, following which glaucoma medications were discontinued, as per predetermined washout periods - five days for carbonic anhydrase inhibitors, 14 days for alpha agonists and 28 days for all other drugs. Absolute change in IOP by withdrawing one medication was 5.4 ± 3.0 mmHg, after two drugs it was 6.9 ± 3.3 mmHg and after withdrawing three drugs it was 9.0 ± 3.8 mmHg. A calculation of the percentage decrease in IOP was made as: IOP change divided by final IOP, and was 23 ± 12%, 28 ± 11% and 34 ± 11 % respectively for one, two and three topical glaucoma medications. Of patients on a prostaglandin analogue, 67% had a decrease in IOP > 20 %.
There are a few limitations of the study. The washout period as ascertained in the only study by Stewart et al.,1 was 3.3. ± 3.0 weeks for brimonidine and 4.4 ± 3.2 weeks for latanoprost. Therefore, the washout periods used in this study appear inadequate for the ascertaining drug efficacy. There was no analysis of change in homogenous groups, using a particular medication/combination of medications. Instead, for example, in single medication analysis, a prostaglandin analogue was analyzed together with a carbonic anhydrase inhibitor or alpha agonist. The analysis of IOP increase - change in IOP divided by IOP ON medication - does not appear as logical as the analysis of IOP decrease, both differ significantly. One hundred and seven of 619 patients, and more significantly 16% of patients using two drugs, did not show an increase in IOP of more than 20%, implying that patients could have been non-responders.
A targeted analysis could have provided better data on the efficacy of each drug or combination used.
References
- Stewart WC, Holmes KT, Johnson MA. Washout periods for brimonidine 0.2% and latanoprost 0.005%. Am J Ophthalmol 2001;131(6):798-799.
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