TIMOLOL MALEATE- timolol maleate solution
Bausch & Lomb Americas Inc.
Timolol Maleate Ophthalmic Solution is a non-selective beta-adrenergic receptor blocking agent. Its chemical name is (-)-1-(tert -butylamino)-3-[(4-morpholino-1,2,5-thiadiazol-3-yl)oxy]-2-propanol maleate (1:1) (salt). Timolol maleate possesses an asymmetric carbon atom in its structure and is provided as the levo-isomer. The optical rotation of timolol maleate is:
Its molecular formula is C13 H24 N4 O3 S•C4 H4 O4 and its structural formula is:
Timolol maleate has a molecular weight of 432.50. It is a white, odorless, crystalline powder which is soluble in water, sparingly soluble in ethanol; slightly soluble in chloroform; practically insoluble in ether. Timolol Maleate Ophthalmic Solution is stable at room temperature.
Timolol Maleate Ophthalmic Solution is supplied as a sterile, isotonic, buffered, aqueous solution of timolol maleate in two dosage strengths. Each mL of Timolol Maleate Ophthalmic Solution 0.25% contains 2.5 mg of timolol (3.4 mg of timolol maleate). The pH of the solution is approximately 7, and the osmolality is 260-340 mOsm/kg. Each mL of Timolol Maleate Ophthalmic Solution 0.5% contains 5 mg of timolol (6.8 mg of timolol maleate). Inactive ingredients: monobasic and dibasic sodium phosphate, sodium hydroxide to adjust pH, and purified water. Benzalkonium chloride 0.01% is added as preservative.
Mechanism of Action
Timolol maleate is a beta1 and beta2 (non-selective) adrenergic receptor blocking agent that does not have significant intrinsic sympathomimetic, direct myocardial depressant, or local anesthetic (membrane-stabilizing) activity.
Beta-adrenergic receptor blockade reduces cardiac output in both healthy subjects and patients with heart disease. In patients with severe impairment of myocardial function, beta-adrenergic receptor blockade may inhibit the stimulatory effect of the sympathetic nervous system necessary to maintain adequate cardiac function.
Beta-adrenergic receptor blockade in the bronchi and bronchioles results in increased airway resistance from unopposed parasympathetic activity. Such an effect in patients with asthma or other bronchospastic conditions is potentially dangerous.
Timolol Maleate Ophthalmic Solution, when applied topically on the eye, has the action of reducing elevated as well as normal intraocular pressure, 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 intraocular pressure, the greater the likelihood of glaucomatous visual field loss and optic nerve damage.
The onset of reduction in intraocular pressure following administration of Timolol Maleate Ophthalmic Solution can usually be detected within one-half hour after a single dose. The maximum effect usually occurs in one to two hours and significant lowering of intraocular pressure can be maintained for periods as long as 24 hours with a single dose. Repeated observations over a period of one year indicate that the intraocular pressure-lowering effect of Timolol Maleate Ophthalmic Solution is well maintained.
The precise mechanism of the ocular hypotensive action of Timolol Maleate Ophthalmic Solution is not clearly established at this time. Tonography and fluorophotometry studies in man suggest that its predominant action may be related to reduced aqueous formation. However, in some studies a slight increase in outflow facility was also observed.
In a study of plasma drug concentration in six subjects, the systemic exposure to timolol was determined following twice daily administration of Timolol Maleate Ophthalmic Solution 0.5%. The mean peak plasma concentration following morning dosing was 0.46 ng/mL and following afternoon dosing was 0.35 ng/mL.
In controlled multiclinic studies in patients with untreated intraocular pressures of 22 mmHg or greater, Timolol Maleate Ophthalmic Solution 0.25% or 0.5% administered twice a day produced a greater reduction in intraocular pressure than 1, 2, 3, or 4% pilocarpine solution administered four times a day or 0.5, 1, or 2% epinephrine hydrochloride solution administered twice a day.
In these studies, Timolol Maleate Ophthalmic Solution was generally well tolerated and produced fewer and less severe side effects than either pilocarpine or epinephrine. A slight reduction of resting heart rate in some patients receiving Timolol Maleate Ophthalmic Solution (mean reduction 2.9 beats/minute standard deviation 10.2) was observed.
INDICATIONS AND USAGE
Timolol Maleate Ophthalmic Solution is indicated in the treatment of elevated intraocular pressure in patients with ocular hypertension or open-angle glaucoma.
Timolol Maleate Ophthalmic Solution is contraindicated in patients with (1) bronchial asthma; (2) a history of bronchial asthma; (3) severe chronic obstructive pulmonary disease [see WARNINGS]; (4) sinus bradycardia; (5) second or third degree atrioventricular block; (6) overt cardiac failure [see WARNINGS]; (7) cardiogenic shock; or (8) hypersensitivity to any component of this product.
As with many topically applied ophthalmic drugs, this drug 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 reactions 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 ophthalmic administration of timolol maleate [see CONTRAINDICATIONS].
Sympathetic stimulation may be essential for support of the circulation in individuals with diminished myocardial contractility, and its inhibition of beta-adrenergic receptor blockade may precipitate more severe 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. At the first sign or symptom of cardiac failure, Timolol Maleate Ophthalmic Solution should be discontinued.
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, in which Timolol Maleate Ophthalmic Solution is contraindicated [see CONTRAINDICATIONS]) should, in general, not receive beta-blockers, including Timolol Maleate Ophthalmic Solution.
The necessity or desirability of withdrawal of beta-adrenergic blocking agents prior to 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 experienced protracted severe hypotension during anesthesia. Difficulty in restarting and maintaining the heartbeat has also been reported. For these reasons, in patients undergoing elective surgery, some authorities recommend gradual withdrawal of beta-adrenergic receptor blocking agents.
If necessary during surgery, the effects of beta-adrenergic blocking agents may be reversed by sufficient doses of adrenergic agonists.
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.
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