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Betoptic S (Betaxolol Hydrochloride Ophthalmic) - Description and Clinical Pharmacology

 
 



DESCRIPTION

BETOPTIC S® Ophthalmic Suspension 0.25% contains betaxolol hydrochloride, a cardioselective beta-adrenergic receptor inhibitor, in a sterile resin suspension formulation. Betaxolol hydrochloride is a white, crystalline powder, with a molecular weight of 343.89. The chemical structure is presented below.


Empirical Formula:
C18H29NO3•HCl
Chemical Name:
(±)-1-[p-[2-(cyclopropylmethoxy) ethyl]phenoxy]-3-(isopropylamino)-2-propanol hydrochloride.

Each mL of BETOPTIC S® Ophthalmic Suspension 0.25% contains: Active: betaxolol HCl 2.8 mg equivalent to 2.5 mg of betaxolol base. Preservative: benzalkonium chloride 0.01%. Inactives: mannitol, poly(styrene-divinyl benzene) sulfonic acid, carbomer 934P, edetate disodium, hydrochloric acid or sodium hydroxide (to adjust pH) and purified water.

BETOPTIC S® Ophthalmic Suspension 0.25% has pH of approximately 7.6 and an osmolality of approximately 290 mOsmol/kg.

CLINICAL PHARMACOLOGY

Mechanism of Action

Betaxolol HCl, a cardioselective (beta-1-adrenergic) receptor inhibitor, does not have significant membrane-stabilizing (local anesthetic) activity and is devoid of intrinsic sympathomimetic action. Orally administered beta-adrenergic receptor inhibitors reduce cardiac output in healthy subjects and patients with heart disease. In patients with severe impairment of myocardial function, beta-adrenergic receptor antagonists may inhibit the sympathetic stimulatory effect necessary to maintain adequate cardiac function.

When instilled in the eye, BETOPTIC S® Ophthalmic Suspension 0.25% has the action of reducing elevated intraocular pressure, whether or not accompanied by glaucoma. Ophthalmic betaxolol has minimal effect on pulmonary and cardiovascular parameters.

Elevated IOP presents a major risk factor in glaucomatous field loss. The higher the level of IOP, the greater the likelihood of optic nerve damage and visual field loss. Betaxolol has the action of reducing elevated as well as normal intraocular pressure and the mechanism of ocular hypotensive action appears to be a reduction of aqueous production as demonstrated by tonography and aqueous fluorophotometry.

Pharmacodynamics

The onset of action with betaxolol can generally be noted within 30 minutes and the maximum effect can usually be detected 2 hours after topical administration. A single dose provides a 12-hour reduction in intraocular pressure. In some patients, the intraocular pressure lowering responses to BETOPTIC S® may require a few weeks to stabilize. As with any new medication, careful monitoring of patients is advised.

Ophthalmic betaxolol solution at 1% (one drop in each eye) was compared to placebo in a crossover study challenging nine patients with reactive airway disease. Betaxolol HCl had no significant effect on pulmonary function as measured by Forced Expiratory Volume in 1 second (FEV1), Forced Vital Capacity (FVC), FEV1/FVC and was not significantly different from placebo. The action of isoproterenol, a beta stimulant, administered at the end of the study was not inhibited by ophthalmic betaxolol.

No evidence of cardiovascular beta adrenergic-blockade during exercise was observed with betaxolol in a double-masked, crossover study in 24 normal subjects comparing ophthalmic betaxolol and placebo for effects on blood pressure and heart rate.

NONCLINICAL TOXICOLOGY

Carcinogenesis, Mutagenesis, Impairment of Fertility

Lifetime studies with betaxolol HCl have been completed in mice at oral doses of 6, 20 or 60 mg/kg/day and in rats at 3, 12 or 48 mg/kg/day; betaxolol HCl demonstrated no carcinogenic effect. Higher dose levels were not tested.

In a variety of in vitro and in vivo bacterial and mammalian cell assays, betaxolol HCl was nonmutagenic.

CLINICAL STUDIES

In controlled, double-masked studies, the magnitude and duration of the ocular hypotensive effect of BETOPTIC S® Ophthalmic Suspension 0.25% and BETOPTIC® Ophthalmic Solution 0.5% were clinically equivalent. BETOPTIC S® Suspension was significantly more comfortable than BETOPTIC® Solution.

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