Betaxolol Other names: Betaxolol hydrochloride

Betaxolol is a cardioselective Beta₁ receptor blocker which, when applied topically to the eye, lowers intraocular pressure. It is thought to produce this effect by reducing the rate of production of aqueous humour.

Betaxolol, a cardioselective (beta₁-adrenergic) receptor blocking agent, does not have significant membrane-stabilising (local anaesthetic) activity and is devoid of intrinsic sympathomimetic action. Orally administered beta-adrenergic blocking agents may 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.

Betaxolol has no significant effect on pulmonary function as measured by FEV1, Forced Vital Capacity (FVC), FEV1/FVC and no evidence of cardiovascular beta-adrenergicblockade during exercise was observed.

When instilled in the eye, betaxolol has the action of reducing elevated as well as normal intraocular pressure (IOP), whether or not accompanied by glaucoma. It is thought to produce this effect by reducing the rate of production of aqueous humour as demonstrated by tonography and aqueous fluorophotometry.

Clinical pharmacology

Several studies have indicated that betaxolol may have a beneficial effect on visual function for up to 48 months in patients with chronic open-angle glaucoma and up to 60 months in patients with ocular hypertension. Moreover there is evidence that betaxolol maintains or increases ocular blood flow/perfusion.

Betaxolol is highly lipophilic which results in good permeation of the cornea, allowing high intraocular levels of the drug. Betaxolol is characterised by its good oral absorption, low first pass loss and a relatively long half-life of approximately 16-22 hours. The elimination of betaxolol is primarily by the renal rather than faecal route. The major metabolic pathways yield two carboxylic acid forms plus unchanged betaxolol in the urine (approximately 16% of the administered dose).

The onset of action of betaxolol can generally be noted within 30 minutes and the maximal effect can usually be detected 2 hours after topical administration. A single dose provides a 12-hour reduction in intraocular pressure.

The polar nature of betaxolol can produce apparent ocular discomfort. In this formulation, betaxolol molecules are ionically bound to the amberlite resin. Upon instillation the betaxolol molecules are displaced by ions in the tear film. This displacement process occurs over several minutes and enhances the ocular comfort observed for betaxolol suspension.

Reproduction studies have been conducted with orally administered betaxolol HCl in rats and rabbits. There was evidence of drug related postimplantation loss in rabbits and rats at dose levels above 12 mg/kg and 128 mg/kg (1500 and 16,000 times the maximum recommended human ocular dose), respectively.