Betimol

BETIMOL- timolol solution
Vistakon Pharmaceuticals LLC

DESCRIPTION

Betimol® (timolol ophthalmic solution), 0.25% and 0.5%, is a non-selective beta-adrenergic antagonist for ophthalmic use. The chemical name of the active ingredient is (S)-1-[(1,1-dimethylethyl)amino]-3-[(4-(4-morpholinyl)-1,2,5-thiadiazol-3-yl]oxy]-2-propanol. Timolol hemihydrate is the levo isomer. Specific rotation is [α]25 405nm =-16° (C=10% as the hemihydrate form in 1N HCl).

The molecular formula of timolol is Formula C13 H24 N4 O3 S and its structural formula is:

Chemical Structure
(click image for full-size original)

Timolol (as the hemihydrate) is a white, odorless, crystalline powder which is slightly soluble in water and freely soluble in ethanol. Timolol hemihydrate is stable at room temperature.

Betimol® is a clear, colorless, isotonic, sterile, microbiologically preserved phosphate buffered aqueous solution.

It is supplied in two dosage strengths, 0.25% and 0.5%.

Each mL of Betimol® 0.25% contains 2.56 mg of timolol hemihydrate equivalent to 2.5 mg Timolol.

Each mL of Betimol® 0.5% contains 5.12 mg of timolol hemihydrate equivalent to 5.0 mg timolol.

Inactive ingredients: monosodium and disodium phosphate dihydrate to adjust pH (6.5 — 7.5) and water for injection, benzalkonium chloride 0.01% added as preservative.

The osmolality of Betimol® is 260 to 320 mOsmol/kg.

CLINICAL PHARMACOLOGY

Timolol is a non-selective beta-adrenergic antagonist.

It blocks both beta1 -and beta2 -adrenergic receptors. Timolol does not have significant intrinsic sympathomimetic activity, local anesthetic (membrane-stabilizing) or direct myocardial depressant activity.

Timolol, when applied topically in the eye, reduces normal and elevated intraocular pressure (IOP) whether or not accompanied by glaucoma. Elevated intraocular pressure is a major risk factor in the pathogenesis of glaucomatous visual field loss. The higher the level of IOP, the greater the likelihood of glaucomatous visual field loss and optic nerve damage. The predominant mechanism of ocular hypotensive action of topical beta-adrenergic blocking agents is likely due to a reduction in aqueous humor production.

In general, beta-adrenergic blocking agents reduce cardiac output both in healthy subjects and patients with heart diseases. In patients with severe impairment of myocardial function, beta-adrenergic receptor blocking agents may inhibit sympathetic stimulatory effect necessary to maintain adequate cardiac function. In the bronchi and bronchioles, beta-adrenergic receptor blockade may also increase airway resistance because of unopposed parasympathetic activity.

Pharmacokinetics

When given orally, timolol is well absorbed and undergoes considerable first pass metabolism. Timolol and its metabolites are primarily excreted in the urine. The half-life of timolol in plasma is approximately 4 hours.

Clinical Studies

In two controlled multicenter studies in the U.S., Betimol® 0.25% and 0.5% were compared with respective timolol maleate eyedrops. In these studies, the efficacy and safety profile of Betimol® was similar to that of timolol maleate.

Betimol Indications and Usage

Betimol® is indicated in the treatment of elevated intraocular pressure in patients with ocular hypertension or open-angle glaucoma.

CONTRAINDICATIONS

Betimol® is contraindicated in patients with overt heart failure, cardiogenic shock, sinus bradycardia, second- or third-degree atrioventricular block, bronchial asthma or history of bronchial asthma, or severe chronic obstructive pulmonary disease, or hypersensitivity to any component of this product.

WARNINGS

As with other topically applied ophthalmic drugs, Betimol® is absorbed systemically. The same adverse reactions found with systemic administration of beta-adrenergic blocking agents may occur with topical administration. For example, severe respiratory and cardiac reactions, including death due to bronchospasm in patients with asthma, and rarely, death in association with cardiac failure have been reported following systemic or topical administration of beta-adrenergic blocking agents.

Cardiac Failure

Sympathetic stimulation may be essential for support of the circulation in individuals with diminished myocardial contractility, and its inhibition by beta-adrenergic receptor blockade may precipitate more severe cardiac failure.

In patients without a history of cardiac failure, continued depression of the myocardium with beta-blocking agents over a period of time can, in some cases, lead to cardiac failure. Betimol® should be discontinued at the first sign or symptom of cardiac failure.

Obstructive Pulmonary Disease

Patients with chronic obstructive pulmonary disease (e.g. chronic bronchitis, emphysema) of mild or moderate severity, bronchospastic disease, or a history of bronchospastic disease (other than bronchial asthma or a history of bronchial asthma which are contraindications) should in general not receive beta-blocking agents.

Major Surgery

The necessity or desirability of withdrawal of beta-adrenergic blocking agents prior to a major surgery is controversial. Beta-adrenergic receptor blockade impairs the ability of the heart to respond to beta-adrenergically mediated reflex stimuli. This may augment the risk of general anesthesia in surgical procedures. Some patients receiving beta-adrenergic receptor blocking agents have been subject to protracted severe hypotension during anesthesia. Difficulty in restarting and maintaining the heartbeat has also been reported. For these reasons, in patients undergoing elective surgery, gradual withdrawal of beta-adrenergic receptor blocking agents is recommended. If necessary during surgery, the effects of beta-adrenergic blocking agents may be reversed by sufficient doses of beta-adrenergic agonists.

Diabetes Mellitus

Beta-adrenergic blocking agents should be administered with caution in patients subject to spontaneous hypoglycemia or to diabetic patients (especially those with labile diabetes) who are receiving insulin or oral hypoglycemic agents. Beta-adrenergic receptor blocking agents may mask the signs and symptoms of acute hypoglycemia.

Thyrotoxicosis

Beta-adrenergic blocking agents may mask certain clinical signs (e.g. tachycardia) of hyperthyroidism. Patients suspected of developing thyrotoxicosis should be managed carefully to avoid abrupt withdrawal of beta-adrenergic blocking agents which might precipitate a thyroid storm.

PRECAUTIONS

General

Because of the potential effects of beta-adrenergic blocking agents relative to blood pressure and pulse, these agents should be used with caution in patients with cerebrovascular insufficiency. If signs or symptoms suggesting reduced cerebral blood flow develop following initiation of therapy with Betimol® , alternative therapy should be considered.

There have been reports of bacterial keratitis associated with the use of multiple dose containers of topical ophthalmic products. These containers had been inadvertently contaminated by patients who, in most cases, had a concurrent corneal disease or a disruption of the ocular epithelial surface. (See PRECAUTIONS, Information for Patients.)

Muscle Weakness

Beta-adrenergic blockade has been reported to potentiate muscle weakness consistent with certain myasthenic symptoms (e.g. dipIopia, ptosis, and generalized weakness). Beta-adrenergic blocking agents have been reported rarely to increase muscle weakness in some patients with myasthenia gravis or myasthenic symptoms.

In angle-closure glaucoma, the goal of the treatment is to reopen the angle. This requires constricting the pupil. Betimol® has no effect on the pupil. Therefore, if timolol is used in angle-closure glaucoma, it should always be combined with a miotic and not used alone.

Anaphylaxis

While taking beta-blockers, patients with a history of atopy or a history of severe anaphylactic reactions to a variety of allergens may be more reactive to repeated accidental, diagnostic, or therapeutic challenge with such allergens. Such patients may be unresponsive to the usual doses of epinephrine used to treat anaphylactic reactions.

The preservative benzalkonium chloride may be absorbed by soft contact lenses. Patients who wear soft contact lenses should wait 5 minutes after instilling Betimol® before they insert their lenses.

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