MK-927: a topically effective carbonic anhydrase inhibitor in patients

Oral acetazolamide for intraocular pressure lowering: balancing efficacy and safety in ophthalmic practice

Introduction: Systemic acetazolamide is an efficacious adjunct to topical therapy to lower intraocular pressure (IOP) in glaucomatous eyes. This article aims to provide a comprehensive review for how best to use the agent in ophthalmic practice.Areas covered: This article will review the history, mechanism of action, methods of observing efficacy, indications for IOP lowering, side effects, allergy information including discussion of limited cross-reactivity between antimicrobial and non-antimicrobial sulfonamides, formulations, dosing and monitoring of acetazolamide. To select articles for this review, an electronic search was conducted using the PubMed database and cross-referencing was conducted for relevant literature.Expert opinion: The benefits of oral carbonic anhydrase inhibitor therapy can outweigh the risks in many circumstances. It is important that eye care practitioners work together with a patient's primary care practitioner to monitor for and mitigate risks. Greater education is needed with regard to the allergy profile of these powerful agents. Though not often a first-line option, oral carbonic anhydrase inhibitors remain pivotal and play in important role in delivery of eye care.

Feline glaucomas

Cats are usually presented at a very late stage in the course of glaucoma when the eye is already blind. Secondary glaucoma because of another underlying ocular lesion is the most common form of glaucoma in the cat and is frequently associated with chronic anterior uveitis or intraocular neoplasia. Chronic stages of glaucoma in the cat are characterized by buphthalmus, anterior lens luxation, and exposure keratitis secondary to the enlarged globe. Ophthalmoscopic signs of glaucomatous retinal degeneration are only noticed in very advanced stages. Treatment of glaucoma in cats is usually aimed to keep the eye comfortable and within a normal intraocular pressure range. However, many antiglaucoma medications that are successfully used in humans and dogs are not very well tolerated by cats and, therefore, the selection of recommended drugs is limited in this species.

Comparative effects of intraocular pressure between systemic and topical carbonic anhydrase inhibitors: a clinical masked, cross-over study

The aims of the following study were to compare the efficacy of Dorzolamide 1% eye drops with systemic Acetazolamide on the ocular pressure diurnal curve in patients with maximal medical therapy. Three ocular pressure curve were performed in glaucomatous patients, already receiving maximal medical therapy. After a baseline curve, patients were pretreated either with Dorzolamide 1% eye drops or 250 mg Acetazolamide tablets in a double-blind cross-over study. Dorzolamide 1% eye drops and 250 mg Acetazolamide tablets significantly reduced intraocular pressure (IOP) at 2 and 4 h after pretreatment. Both treatments caused a significantly additional decrease of IOP despite maximal medical therapy. Dorzolamide 1% eye drops is as effective as Acetazolamide tablets in reducing the IOP curve. Topical carbonic anhydrase inhibitors may represent an additional and safer treatment for those patients with uncontrolled medical glaucoma.

A comparison of dorzolamide and timolol in patients with pseudoexfoliation and glaucoma or ocular hypertension

PURPOSE

The purpose of the study is to compare the efficacy and safety profile of 2.0% dorzolamide (three times daily) and 0.5% timolol (twice daily) for up to 6 months in patients with glaucoma or ocular hypertension associated with pseudoexfoliation. The additive effects of dorzolamide and timolol in patients requiring add-on therapy also was evaluated.

METHODS

This was a double-masked, randomized, parallel comparison study at 15 Scandinavian sites. One hundred eighty-four patients with pseudoexfoliation and either glaucoma or ocular hypertension who were 21 to 85 years of age were studied. The treatment groups were 2.0% dorzolamide three times daily and 0.5% timolol maleate twice daily.

RESULTS

At 6 months, the mean percent reduction in intraocular pressure of 2% dorzolamide and 0.5% timolol was 24% and 29%, respectively, at morning peak and 21% and 23%, respectively, at afternoon trough. The additional intraocular pressure-lowering effect of adding 2.0% dorzolamide twice daily to patients receiving timolol was 14% and 15%, at peak and trough, respectively. There were no differences between treatment groups in the incidence of clinical adverse experiences, and dorzolamide was not associated with the systemic adverse effects typically ascribed to the use of oral carbonic anhydrase inhibitors.

CONCLUSION

Two percent dorzolamide (three times daily) was effective and well tolerated in patients with glaucoma or ocular hypertension associated with pseudoexfoliation over the course of 6 months; 0.5% timolol (twice daily) had a greater level of intraocular pressure-lowering activity than did dorzolamide, although the difference between the two treatments became less pronounced during the study period. Finally, 2.0% dorzolamide (twice daily) produced additional lowering of intraocular pressure when given with 0.5% timolol (twice daily).

A clinical trial of MK-507, Trusopt, for raised intraocular pressure--the Australian experience

BACKGROUND

Since the introduction of carbonic anhydrase inhibitors, a topical preparation has been sought to avoid the complications of systemic medication while retaining the effect of lowering intraocular pressure. Recently, a topical carbonic anhydrase inhibitor, MK-507, has been found superior to others and introduced for multicentre clinical trial.

PATIENTS AND METHODS

As part of an international multicentre trial, we compared MK-507 with beta blockers for one year in 20 patients with raised intraocular pressure, both as monotherapy and in combination.

RESULTS

Twelve patients with a mean peak pressure of 31.9 +/- 6.8 mmHg (range, 22 to 49 mmHg) off all medication received MK-507. After two weeks, mean peak pressure was 24.7 +/- 6.1 mmHg (range, 14 to 41 mmHg)--a 22.6% fall in pressure. Six of these patients had a mean peak pressure of 27.8 +/- 6.4 mmHg (range, 21 to 41 mmHg), a fall of 19.2% from day one and were given timolol as add-on therapy. This resulted in a fall to 19.1 +/- 2.8 (range, 15 to 24 mmHg) at year one, a fall of 31.3% after add-on. Four patients on timolol and four on betaxolol gave similar falls in pressure with an additional fall when MK-507 was used as add-on therapy.

CONCLUSIONS

MK-507 demonstrated its effectiveness as an ocular hypotensive agent in this trial of patients with an unusually high rise in pressure. It showed a hypotensive effect roughly equivalent to beta blockers. It is likely that either a topical carbonic anhydrase inhibitor or a cardioselective beta blocker will be the medication of first choice in newly diagnosed glaucoma.

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.

New developments in the drug treatment of glaucoma

This article reviews standard treatment modalities for patients with glaucoma and describes 3 classes of drugs which are undergoing development: apraclonidine (aplonidine, ALO 2145), an alpha 2-adrenergic agonist which has been released for clinical use; topical carbonic anhydrase inhibitors, a modification of the systemic carbonic anhydrase inhibitors currently in use; and prostaglandins (PGs), a new class of drugs with topical ocular hypotensive activity. Standard treatment modalities include parasympathomimetic agents such as pilocarpine, carbachol, and phospholine iodide, which lower intraocular pressure (IOP) by increasing aqueous outflow through the trabecular meshwork. A newer form of pilocarpine as a gel produces a longer action. Adrenergic agonist medications, such as epinephrine (adrenaline) and its prodrug dipivefrine (dipivalyl epinephrine), function by increasing uveoscleral outflow and trabecular outflow facility. A decrease in aqueous formation by the ciliary processes is thought to be the mechanism of action of beta-adrenoceptor antagonists, but the physiological basis for this action has not been clearly demonstrated. A newer beta-blocker, betaxolol, has relatively selective beta 1-blocking activity. Carbonic anhydrase inhibitors are nonbacteriostatic sulphonamide derivatives which decrease aqueous formation by the ciliary body. Almost 50% of patients taking these medications are unable to tolerate them because of their adverse effects, and there is thus much interest in the development of a topical carbonic anhydrase inhibitor with the potential for fewer adverse effects. MK 507 is the most recent and most potent compound in the series of topically active carbonic anhydrase inhibitors. Apraclonidine hydrochloride is a derivative of clonidine hydrochloride, an alpha 2-adrenergic agonist. Clonidine has previously been shown to lower IOP significantly, but has the potential to produce marked lowering of both systolic and diastolic blood pressures. Its major ocular effect appears to be a decrease in aqueous production. The structural modification to apraclonidine decreases corneal absorption and the drug's ability to cross the blood-brain barrier, minimising the risk of centrally mediated cardiovascular side effects. Apraclonidine may also influence secondary avenues of aqueous outflow, such as uveoscleral outflow, and may also affect conjunctival and episcleral vascular flow. It produces a mean decrease in IOP of 25% for as long as 12 hours. Adverse effects include blanching of the conjunctiva, minimal mydriasis and eyelid retraction. This drug has been approved in the US for use in prevention of elevated IOP after argon laser trabeculoplasty and iridotomy, and has potential uses in preventing an IOP rise after YAG laser posterior capsulotomy and cataract surgery in patients already on other antiglaucomatous medications.(ABSTRACT TRUNCATED AT 400 WORDS)

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.

A comparison of L-671,152 and MK-927, two topically effective ocular hypotensive carbonic anhydrase inhibitors, in experimental animals

L-671,152 is a water-soluble, carbonic anhydrase inhibitor structurally similar to MK-927, a carbonic anhydrase inhibitor that, on topical administration, lowers the intraocular pressure (IOP) of experimental animals and humans. L-671,152 was more potent than MK-927 at inhibiting purified, human erythrocyte carbonic anhydrase II in vitro, as reflected in their respective IC50 values of 0.16 nM and 1.19 nM. Both compounds were compared for topical, ocular hypotensive activity in pigmented rabbits and cynomolgus monkeys. Ocular hypertension was induced in the latter by argon laser photocoagulation of the trabecular meshwork. A 2% solution of L-671,152 was more potent than 2% MK-927 in lowering the IOP of ocular hypertensive monkeys, the maximum reductions being 13.8 mm Hg (37%) and 9.6 mm Hg (27%) at 5 hr and 4 hr, respectively. Moreover, the duration of action of L-671,152 was superior to that of MK-927. The ocular hypotensive effect of L-671,152 was greater than that of MK-927 over a range of concentrations (0.5%-2%) in pigmented rabbits whose IOP was inherently elevated. The peak declines in the IOP of these rabbits after the instillation of 2% solutions of L-671,152 and MK-927 were 6.1 mm Hg and 4.8 mm Hg, respectively. L-671,152 was very effective in lowering the elevated IOP of alpha-chymotrypsinized rabbits and the unilateral instillation of 0.5% L-671,152 into the contralateral eye failed to decrease the elevated IOP of the alpha-chymotrypsinized eye. This finding indicates that the site of action of topically applied L-671,152 is local. The enhancement in the potency of L-671,152 over MK-927 is attributed to a greater inhibition of carbonic anhydrase activity.