Dorzolamide HCl (Page 2 of 3)

8.4 Pediatric Use

Safety and effectiveness of dorzolamide hydrochloride ophthalmic solution have been demonstrated in pediatric patients in a 3-month, multicenter, double-masked, active-treatment-controlled trial.

8.5 Geriatric Use

No overall differences in safety or effectiveness have been observed between elderly and younger patients.

8.6 Renal and Hepatic Impairment

Dorzolamide has not been studied in patients with severe renal impairment (CrCl less than 30 mL/min). Because dorzolamide and its metabolite are excreted predominantly by the kidney, dorzolamide hydrochloride ophthalmic solution is not recommended in such patients.

Dorzolamide has not been studied in patients with hepatic impairment and should therefore be used with caution in such patients.

10 OVERDOSAGE

Electrolyte imbalance, development of an acidotic state, and possible central nervous system effects may occur. Serum electrolyte levels (particularly potassium) and blood pH levels should be monitored.

11 DESCRIPTION

Dorzolamide hydrochloride ophthalmic solution, USP is a carbonic anhydrase inhibitor formulated for topical ophthalmic use.

Dorzolamide hydrochloride, USP is described chemically as: (4S-trans)-4-(ethylamino)-5,6-dihydro-6methyl-4H -thieno[2,3-b ]thiopyran-2-sulfonamide 7,7-dioxide monohydrochloride. Dorzolamide hydrochloride, USP is optically active. The specific rotation is

The specific rotation is 25 (C=1)= -17
(click image for full-size original)

Its empirical formula is C10 H16 N2 O4 S3 •HCl and its structural formula is:

The structural formula for Dorzolamide hydrochloride, USP is described chemically as: (4S-trans)-4-(ethylamino)-5,6-dihydro-6¬methyl-4H-thieno[2,3-b]thiopyran-2-sulfonamide 7,7-dioxide monohydrochloride. Dorzolamide hydrochloride, USP is optically active. The specific rotation is

Dorzolamide hydrochloride, USP has a molecular weight of 360.9 and a melting point of about 264°C. It is a white to off-white, crystalline powder, which is soluble in water and slightly soluble in methanol and ethanol.

Dorzolamide hydrochloride sterile ophthalmic solution, USP is supplied as a sterile, isotonic, buffered, slightly viscous, aqueous solution of dorzolamide hydrochloride. The pH of the solution is approximately 5.6, and the osmolarity is 260-330 mOsM. Each mL of dorzolamide hydrochloride ophthalmic solution, USP 2% contains 20 mg dorzolamide (22.3 mg of dorzolamide hydrochloride, USP). Inactive ingredients are hydroxyethyl cellulose, mannitol, sodium citrate dihydrate, sodium hydroxide (to adjust pH) and water for injection. Benzalkonium chloride 0.0075% is added as a preservative.

12 CLINICAL PHARMACOLOGY

12.1 Mechanism of Action

Carbonic anhydrase (CA) is an enzyme found in many tissues of the body including the eye. It catalyzes the reversible reaction involving the hydration of carbon dioxide and the dehydration of carbonic acid. In humans, carbonic anhydrase exists as a number of isoenzymes, the most active being carbonic anhydrase II (CA-II), found primarily in red blood cells (RBCs), but also in other tissues. Inhibition of carbonic anhydrase in the ciliary processes of the eye decreases aqueous humor secretion, presumably by slowing the formation of bicarbonate ions with subsequent reduction in sodium and fluid transport. The result is a reduction in intraocular pressure (IOP).

Dorzolamide hydrochloride ophthalmic solution contains dorzolamide hydrochloride, an inhibitor of human carbonic anhydrase II. Following topical ocular administration, dorzolamide hydrochloride ophthalmic solution reduces elevated intraocular pressure. Elevated intraocular pressure is a major risk factor in the pathogenesis of optic nerve damage and glaucomatous visual field loss.

12.3 Pharmacokinetics

When topically applied, dorzolamide reaches the systemic circulation. To assess the potential for systemic carbonic anhydrase inhibition following topical administration, drug and metabolite concentrations in RBCs and plasma and carbonic anhydrase inhibition in RBCs were measured.

Dorzolamide accumulates in RBCs during chronic dosing as a result of binding to CA-II. The parent drug forms a single N-desethyl metabolite, which inhibits CA-II less potently than the parent drug but also inhibits CA-I. The metabolite also accumulates in RBCs where it binds primarily to CA-I. Plasma concentrations of dorzolamide and metabolite are generally below the assay limit of quantitation (15nM). Dorzolamide binds moderately to plasma proteins (approximately 33%).

Dorzolamide is primarily excreted unchanged in the urine; the metabolite also is excreted in urine. After dosing is stopped, dorzolamide washes out of RBCs nonlinearly, resulting in a rapid decline of drug concentration initially, followed by a slower elimination phase with a half-life of about four months.

To simulate the systemic exposure after long-term topical ocular administration, dorzolamide was given orally to eight healthy subjects for up to 20 weeks. The oral dose of 2 mg twice daily closely approximates the amount of drug delivered by topical ocular administration of dorzolamide 2% three times daily. Steady state was reached within 8 weeks. The inhibition of CA-II and total carbonic anhydrase activities was below the degree of inhibition anticipated to be necessary for a pharmacological effect on renal function and respiration in healthy individuals.

13 NONCLINICAL TOXICOLOGY

13.1 Carcinogenesis, Mutagenesis, Impairment of Fertility

In a two-year study of dorzolamide hydrochloride administered orally to male and female Sprague-Dawley rats, urinary bladder papillomas were seen in male rats in the highest dosage group of 20 mg/kg/day. Papillomas were not seen in rats given oral doses of 1 mg/kg/day. These doses represent estimated plasma Cmax levels in rats, 138 and 7 times higher than the lower limit of detection in human plasma following ocular administration, respectively.

No treatment-related tumors were seen in a 21-month study in female and male mice given oral doses up to 75 mg/kg/day. This dose represents an estimated plasma Cmax level in mice, 582 times higher than the lower limit of detection in human plasma following ocular administration.

The increased incidence of urinary bladder papillomas seen in the high-dose male rats is a class-effect of carbonic anhydrase inhibitors in rats. Rats are particularly prone to developing papillomas in response to foreign bodies, compounds causing crystalluria, and diverse sodium salts.

No changes in bladder urothelium were seen in dogs given oral dorzolamide hydrochloride for one year at 2 mg/kg/day or monkeys dosed topically to the eye for one year. An oral dose of 2 mg/kg/day in dogs represents an estimated plasma Cmax level, 137 times higher than the lower limit of detection in human plasma following ocular administration. The topical ophthalmic dose in monkeys was approximately equivalent to the human topical ophthalmic dose.

The following tests for mutagenic potential were negative: (1) in vivo (mouse) cytogenetic assay;

(2) in vitro chromosomal aberration assay; (3) alkaline elution assay; (4) V-79 assay; and (5) Ames test.

In reproduction studies of dorzolamide hydrochloride in rats, there were no adverse effects on the reproductive capacity of males or females at doses of 15 and 7.5 mg/kg/day, respectively. These doses represent estimated plasma Cmax levels in rats, 104 and 52 times higher than the lower limit of detection in human plasma following ocular administration, respectively.

14 CLINICAL STUDIES

The efficacy of dorzolamide hydrochloride ophthalmic solution was demonstrated in clinical studies in the treatment of elevated intraocular pressure in patients with glaucoma or ocular hypertension (baseline IOP greater than or equal to 23 mmHg). The IOP-lowering effect of dorzolamide hydrochloride ophthalmic solution was approximately 3 to 5 mmHg throughout the day and this was consistent in clinical studies of up to one year duration.

The efficacy of dorzolamide hydrochloride ophthalmic solution when dosed less frequently than three times a day (alone or in combination with other products) has not been established.

In a one year clinical study, the effect of dorzolamide hydrochloride ophthalmic solution 2% three times daily on the corneal endothelium was compared to that of betaxolol ophthalmic solution twice daily and timolol maleate ophthalmic solution 0.5% twice daily. There were no statistically significant differences between groups in corneal endothelial cell counts or in corneal thickness measurements. There was a mean loss of approximately 4% in the endothelial cell counts for each group over the one year period.

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