MK-927, a topical carbonic anhydrase inhibitor. Dose response and reproducibility

Comparison of topical brinzolamide 1% and dorzolamide 2% eye drops given twice daily in addition to timolol 0.5% in patients with primary open-angle glaucoma or ocular hypertension

PURPOSE

The aim was to compare topical brinzolamide 1% twice daily with dorzolamide 2% twice daily, each given with timolol 0.5% twice daily, for safety and effects on intraocular pressure in patients with primary open-angle glaucoma or ocular hypertension.

METHODS

This double-blind, randomized, active controlled, parallel group study was conducted multinationally at 31 sites, in 241 patients as above, with assessments at baseline and monthly during 3 months of treatment. The primary end point was a diurnal reduction of trough/peak intraocular pressure from a timolol 0.5% twice daily baseline.

RESULTS

Both treatment regimens reduced intraocular pressure significantly at all time points (P <.001): brinzolamide plus timolol by -3.6 to -5.3 mm Hg (-14.2 to -21.9%), dorzolamide plus timolol by -3.6 mm Hg to -5.1 mm Hg (-14.1 to -21.2%). Clinically relevant intraocular pressure reductions (decreases 5 mm Hg or greater or absolute intraocular pressure values 21 mm Hg or less) were manifested by 50.0% to 89.3% of patients under brinzolamide plus timolol and by 43.9% to 85.4% under dorzolamide plus timolol. The treatments were equivalent in mean intraocular pressure-lowering. In general, both regimens were well tolerated. However, more patients (P =.001) experienced at least one adverse event with dorzolamide plus timolol (32.8%) as compared with brinzolamide plus timolol (14.7%); also, more patients (P =.001) experienced ocular discomfort (stinging and burning) after dorzolamide plus timolol (13.1%) than after brinzolamide plus timolol (1.7%).

CONCLUSIONS

In terms of intraocular pressure reduction, brinzolamide 1% twice daily was equivalent to dorzolamide 2% twice daily, each added to timolol 0.5% twice daily, but brinzolamide produced significantly less ocular burning and stinging.

Topical carbonic anhydrase inhibition increases ocular pulse amplitude in high tension primary open angle glaucoma

BACKGROUND

Ocular pulse amplitude (OPA) is reduced in normal tension primary open angle glaucoma (NTP) patients when compared with healthy age matched controls (CTL) while increased OPA appears to protect ocular hypertensive patients from visual field loss. If NTP is accompanied by vasospasm, as in roughly half of the primary open angle glaucoma (POAG) population (independent of intraocular pressure, IOP), calcium channel blockers increase OPA and thus stabilise visual fields in these patients. Current glaucoma drugs reduce IOP but do not activate (compromised) ocular perfusion.

METHODS

The influence of dorzolamide, a topical carbonic anhydrase inhibitor in standard dosage (three times daily, one eye) on OPA, IOP, blood pressure, and heart rate was investigated in a randomised, prospective, masked clinical trial assessing the acute effects of dorzolamide v placebo before and 2 days after application in 33 cataract patients with (n = 14) and without (n = 19) high tension POAG (HTP) who provided informed consent.

RESULTS

Following application of dorzolamide (D) IOP (mm Hg, mean (SEM)) in HTPD (20.2 (0.5)/16.3 (0.5) and in CTLD (16.0 (0.5)/12.3 (0.5)) was highly significantly (p < 0.001) reduced and was significantly (p < 0.03) reduced in vehicle (V) treated eyes (HTPv: 20.3 (0.4)/19.0 (0.4)) and CTLv: 15.8 (0.4)/14.9 (0.3)) when compared with respective baseline measurements. OPA (mm Hg) in HTPD (2.1 (0.1)/2.5 (0.1)) and CTLD (2.2 (0.1)/2.6 (0.2)) eyes was significantly (p < 0.05) increased and unaffected in vehicle treated eyes when compared with respective baseline measurements. Systemic perfusion variables were also unchanged.

CONCLUSION

Dorzolamide increased OPA in HTP and CTL. Drugs stimulating OPA may improve prognosis of POAGs.

Dorzolamide: development and clinical application of a topical carbonic anhydrase inhibitor

Systemic carbonic anhydrase inhibitors are among the most powerful agents to lower intraocular pressure. Unfortunately, their use is frequently accompanied by undesired side effects. Some are due to the relatively large amounts of drug that have to be systemically administered to inhibit the carbonic anhydrase in the ciliary processes. Recently, dorzolamide, a topical carbonic anhydrase inhibitor, has become commercially available for clinical use. This article reviews the development of topical carbonic anhydrase inhibitors with special reference to dorzolamide. When administered three-times daily, dorzolamide lowers intraocular pressure in a clinically useful manner. Ocular side-effects include frequent stinging and burning and allergy can develop. Systemic side effects have not been observed that could definitively be related to inhibition of extraocular carbonic anhydrase. Blood dyscrasias have not yet been observed. Absence of cardiovascular and pulmonary side effects, as can occur with beta adrenergic antagonists, and lack of pupillary and accommodative stimulation, as occur with cholinergic agonists, might make dorzolamide first-line medical treatment for elevated intraocular pressure.

Pharmacological advances in the treatment of glaucoma

Glaucoma is a potentially blinding disease. The goal of glaucoma therapy is to reduce intraocular pressure to a predetermined target level. There are currently 5 classes of compounds used for the medical management of glaucoma. Four classes that appear promising for the long term management of glaucoma are in different phases of clinical investigation, and include the topically active carbonic anhydrase inhibitors, selective alpha 2-adrenergic agonists, prostaglandins and ethacrynic acid. The topically active carbonic anhydrase inhibitor dorzolamide (MK-507) is effective and well tolerated in clinical trials of up to 1 year's duration. Animal studies have demonstrated that this drug lowers intraocular pressure by reducing aqueous humour formation. The selective alpha 2-adrenergic agonists, brimonidine and apraclonidine, have been shown to be effective in reducing intraocular pressure in the short term. Long term effectiveness of these agents is under investigation. Prostaglandins (PG) of the PGF2-alpha isopropylester series caused marked reductions of intraocular pressure in laboratory and clinical trials. The newest prostaglandin analogue, latanoprost (PhXA41), effectively lowered intraocular pressure and was well tolerated in clinical trials of up to 4 weeks' duration. Prostaglandins reduce intraocular pressure by enhancing uveoscleral outflow. Ethacrynic acid enhanced traditional outflow facility and lowered intraocular pressure when applied topically or intracamerally in laboratory studies and clinical trials. Corneal adverse effects of ethacrynic acid have been noted. Reformulation of ethacrynic acid ointment may resolve this problem. These 4 classes of compounds will enhance our options for the medical management of glaucoma. They may be used instead of or in combination with some of the drugs currently in use, and may be better tolerated.

Two topical carbonic anhydrase inhibitors sezolamide and dorzolamide in Gelrite vehicle: a multiple-dose efficacy study

The ocular hypotensive activities of the two potent topical carbonic anhydrase inhibitors sezolamide (previously known as MK-417) and dorzolamide (previously known as MK-507 and L-671,152) were compared formulated in Gelrite vehicle, a novel ophthalmic drug delivery system. This was a four-center, double-blind, randomized, placebo-controlled, parallel study in 73 patients with a diagnosis of bilateral primary open-angle glaucoma or ocular hypertension and a morning intraocular pressure (IOP) of greater than 23 mmHg in both eyes following washout of ocular hypotensive medications. Parallel 12-h modified diurnal curves were performed prestudy and on day 6, with a 4-h IOP curve on day 1. On day 6 the peak mean percentage decrease in IOP from baseline occurred 4 h after the dose of dorzolamide (22.1%) and 6 h after the dose of sezolamide (21.3%). There were no significant differences between 2% dorzolamide and 1.8% sezolamide at any time point, although the decrease in IOP for sezolamide tended to be slightly greater than that for dorzolamide. Duration of action of both compounds was, at most, slightly prolonged by the use of Gelrite vehicle when compared with former studies on sezolamide and dorzolamide.

Sezolamide: additivity to timolol twice daily

Sezolamide, a potent topical carbonic anhydrase inhibitor previously known as MK-417, was studied to determine its ocular hypotensive activity in patients with elevated intraocular pressure while on continuing therapy with topical timolol. This was a three-centre, double-masked, randomised, placebo-controlled, parallel study in 36 patients with bilateral primary open angle glaucoma or ocular hypertension on therapy receiving 0.5% timolol twice daily, with a morning intraocular pressure greater than or equal to 22 mmHg in both eyes 2-4 hours following an 8 a.m. dose of timolol. Sezolamide 1.8% or placebo twice daily was added to treatment with timolol on the evening of day 1 and continued for 2 weeks. Twelve-hour diurnal curves were performed before the study on day 1 (timolol alone) and on day 15. Intraocular pressure measurements were also taken on days 2 and 8 at 8 a.m. and 9 a.m. Patients who received timolol and sezolamide showed additional intraocular pressure reductions from day 1 (timolol alone) of 8.0 to 15.5%, which were significant at all times. At hours 1, 2, 4 and 8 the reductions in intraocular pressure observed in the group receiving sezolamide and timolol were significantly greater than those in the group receiving timolol and placebo.

Effect of the application of acetazolamide soaked contact lenses on intraocular pressure of rabbits

Topical application of acetazolamide has no known effect on intraocular pressure (IOP). We tried to detect the hypotensive effect on IOP of acetazolamide soaked onto soft contact lenses (CL). We applied CLs soaked in either 1%, 3%, or 5% acetazolamide solution onto one eye of 29 rabbits while the contralateral eye served as a control. There was an average 32% reduction of IOP amongst all acetazolamide applied eyes, and an average 19% reduction of IOP amongst all control eyes. Amongst the 1% acetazolamide-CL applied eyes there was a mean 37% reduction of IOP, amongst the 3% acetazolamide-CL applied eyes a mean 36% reduction, amongst the 5% acetazolamide-CL applied a mean 30% reduction, and a mean 19% reduction in control eyes. The longest period of IOP reduction followed the application of 1% acetazolamide-CLs, probably owing to improved drug corneal penetration at this concentration. Our results reveal that the application of acetazolamide soaked soft CLs has a significant hypotensive effect on IOP in both the applied and contralateral control eyes of rabbits.

MK-507 versus sezolamide. Comparative efficacy of two topically active carbonic anhydrase inhibitors

Topical carbonic anhydrase inhibitors MK-507 and sezolamide hydrochloride (previously known as MK-417) were compared in a double-masked, randomized, placebo-controlled study in 82 patients with bilateral primary open-angle glaucoma or ocular hypertension. MK-507 was given every 8 or 12 hours, sezolamide every 8 hours, or placebo every 8 or 12 hours for 4 days. Both drugs lowered intraocular pressure (IOP) substantially. MK-507 was somewhat more active than sezolamide, with a peak mean IOP reduction of 26.2% for MK-507 versus 22.5% for sezolamide, although the difference between the treatments was not statistically significant. These drugs may have potential in the treatment of glaucoma.