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    Sustained-release topical rings promising for glaucoma

    Study aims to compare effectiveness, safety of rings versus eye drops


    The two study arms were well-matched demographically. The mean age was 65.6 years; 41%  were male. Sixty-four percent of the bimatoprost patients and 60.6% of the timolol patients had glaucoma; the remainder had ocular hypertension. Mean central corneal thickness was 552.9 µm at baseline in the bimatoprost patients and 564.4 µm in the timolol patients. Inclusion criteria specified a mean IOP (after washout) of 23-34 mm Hg at 8 a.m. and 20-34 mm Hg 2 and 8 hours after the first measurement.

    The investigators compared the bimatoprost rings to timolol using a statistical model of noninferiority. The test criterion for the non-inferiority test was that the upper limit of the 95% confidence interval of the difference between the mean reduction in IOP for the bimatoprost ring arm as compared to the timolol arm should be within 1.5 mm Hg. This statistical test was conducted at three time points (8 a.m., 10 a.m., 4 p.m.) at weeks 2, 6, and 12 (and was calculated, but not formally tested, at months 4, 5, and 6).

    A single administration of the bimatoprost ring provided sustained IOP reduction for six months. The statistical test was successfully met at most but not all of the time points; however, the study was underpowered relative to the treatment effect observed in this phase II study. In phase III studies, the statistical confidence intervals will be smaller due to the larger sample number of patients enrolled. The smaller confidence intervals will make it easier to meet the statistical non-inferiority test described above. “We anticipate in a much larger study that bimatoprost ring and timolol eye drops will be statistically very close to each other if not the same,” Dr. Brandt said.

    The bimatoprost insert appeared less effective than one might expect with bimatoprost eye drops, even though the dose delivered by the ring is similar to the total dose delivered by once-daily drops of 0.03% bimatoprost ophthalmic solution. This finding was consistent with an earlier finding that bimatoprost (and other prostaglandins) becomes less effective the more frequently it is administered, as was demonstrated in the phase III bimatoprost (Lumigan, Allergan studies.2To provide additional IOP-lowering, a ring may be developed that can elute more than one IOP-lowering drug.

    The vast majority of the patients kept the rings in their eyes without the aid of their physician for the duration of the study. At 12 weeks the bilateral retention rate was 93.1% and at six months it was 88.5%.

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