"What are beta blockers and how do they work?
Beta blockers, also known as beta-adrenergic blocking agents, are a class of drugs that works by blocking the neurotransmitters norepinephrine and epinephrine from binding to receptors. "...
Sympathetic stimulation may be a vital component supporting circulatory function in congestive heart failure, and beta-adrenergic receptor blockade carries the potential hazard of further depressing myocardial contractility and precipitating more severe heart failure. In hypertensive patients who have congestive heart failure controlled by digitalis and diuretics, beta-blockers should be administered cautiously. Both digitalis and beta-adrenergic receptor blocking agents slow AV conduction.
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. Therefore at the first sign or symptom of cardiac failure, discontinuation of Kerlone (betaxolol hydrochloride) should be considered. In some cases beta-blocker therapy can be continued while cardiac failure is treated with cardiac glycosides, diuretics, and other agents, as appropriate.
Exacerbation of angina pectoris upon withdrawal
Abrupt cessation of therapy with certain beta-blocking agents in patients with coronary artery disease has been followed by exacerbations of angina pectoris and, in some cases, myocardial infarction has been reported. Therefore, such patients should be warned against interruption of therapy without the physician's advice. Even in the absence of overt angina pectoris, when discontinuation of Kerlone (betaxolol hydrochloride) is planned, the patient should be carefully observed and therapy should be reinstituted, at least temporarily, if withdrawal symptoms occur.
PATIENTS WITH BRONCHOSPASTIC DISEASE SHOULD NOT IN GENERAL RECEIVE BETA-BLOCKERS. Because of its relative β1 selectivity (cardioselectivity), low doses of Kerlone (betaxolol hydrochloride) may be used with caution in patients with bronchospastic disease who do not respond to or cannot tolerate alternative treatment. Since β1 selectivity is not absolute and is inversely related to dose, the lowest possible dose of Kerlone (betaxolol hydrochloride) should be used (5 to 10 mg once daily) and a bronchodilator should be made available. If dosage must be increased, divided dosage should be considered to avoid the higher peak blood levels associated with once-daily dosing.
Anesthesia and major surgery
The necessity, or desirability, of withdrawal of a beta-blocking therapy prior to major surgery is controversial. Beta-adrenergic receptor blockade impairs the ability of the heart to respond to beta-adrenergically mediated reflex stimuli. While this might be of benefit in preventing arrhythmic response, the risk of excessive myocardial depression during general anesthesia may be increased and difficulty in restarting and maintaining the heart beat has been reported with beta-blockers. If treatment is continued, particular care should be taken when using anesthetic agents which depress the myocardium, such as ether, cyclopropane, and trichloroethylene, and it is prudent to use the lowest possible dose of Kerlone (betaxolol hydrochloride) . Kerlone (betaxolol hydrochloride) , like other beta-blockers, is a competitive inhibitor of beta-receptor agonists and its effect on the heart can be reversed by cautious administration of such agents (eg, dobutamine or isoproterenol-see OVERDOSAGE). Manifestations of excessive vagal tone (eg, profound bradycardia, hypotension) may be corrected with atropine 1 to 3 mg IV in divided doses.
Diabetes and hypoglycemia
Beta-blockers should be used with caution in diabetic patients. Beta-blockers may mask tachycardia occurring with hypoglycemia (patients should be warned of this), although other manifestations such as dizziness and sweating may not be significantly affected. Unlike nonselective beta-blockers, Kerlone (betaxolol hydrochloride) does not prolong insulin-induced hypoglycemia.
Beta-adrenergic blockade may mask certain clinical signs of hyperthyroidism (eg, tachycardia). Abrupt withdrawal of beta-blockade might precipitate a thyroid storm; therefore, patients known or suspected of being thyrotoxic from whom Kerlone (betaxolol hydrochloride) is to be withdrawn should be monitored closely (see DOSAGE AND ADMINISTRATION: Cessation of therapy).
Kerlone (betaxolol hydrochloride) should not be given to patients with untreated pheochromocytoma.
Beta-adrenoceptor blockade can cause reduction of intraocular pressure. Since betaxolol hydrochloride is marketed as an ophthalmic solution for treatment of glaucoma, patients should be told that Kerlone (betaxolol hydrochloride) may interfere with the glaucoma-screening test. Withdrawal may lead to a return of increased intraocular pressure. Patients receiving beta-adrenergic blocking agents orally and beta-blocking ophthalmic solutions should be observed for potential additive effects either on the intraocular pressure or on the known systemic effects of beta-blockade.
The value of using beta-blockers in psoriatic patients should be carefully weighed since they have been reported to cause an aggravation in psoriasis.
Impaired hepatic or renal function
Kerlone (betaxolol hydrochloride) is primarily metabolized in the liver to metabolites that are inactive and then excreted by the kidneys; clearance is somewhat reduced in patients with renal failure but little changed in patients with hepatic disease. Dosage reductions have not routinely been necessary when hepatic insufficiency is present (see DOSAGE AND ADMINISTRATION) but patients should be observed. Patients with severe renal impairment and those on dialysis require a reduced dose. (See DOSAGE AND ADMINISTRATION).
Carcinogenesis, mutagenesis, impairment of fertility
Lifetime studies with betaxolol HCl in mice at oral dosages of 6, 20, and 60 mg/kg/day (up to 90 x the maximum recommended human dose [MRHD] based on 60-kg body weight) and in rats at 3, 12, or 48 mg/kg/day (up to 72 x MRHD) showed no evidence of a carcinogenic effect. In a variety of in vitro and in vivobacterial and mammalian cell assays, betaxolol HCl was nonmutagenic. Betaxolol did not adversely affect fertility or mating performance of male or female rats at doses up to 256 mg/kg/day (380 x MRHD).
Pregnancy Category C. In a study in which pregnant rats received betaxolol at doses of 4, 40, or 400 mg/kg/day, the highest dose (600 x MRHD) was associated with increased postimplantation loss, reduced litter size and weight, and an increased incidence of skeletal and visceral abnormalities, which may have been a consequence of drug-related maternal toxicity. Other than a possible increased incidence of incomplete descent of testes and sternebral reductions, betaxolol at 4 mg/kg/day and 40 mg/kg/day (6 x MRHD and 60 x MRHD) caused no fetal abnormalities. In a second study with a different strain of rat, 200 mg betaxolol/kg/day (300 x MRHD) was associated with maternal toxicity and an increase in resorptions, but no teratogenicity. In a study in which pregnant rabbits received doses of 1, 4, 12, or 36 mg betaxolol/kg/day (54 x MRHD), a marked increase in post-implantation loss occurred at the highest dose, but no drug-related teratogenicity was observed. The rabbit is more sensitive to betaxolol than other species because of higher bioavailability resulting from saturation of the first-pass effect. In a peri- and postnatal study in rats at doses of 4, 32, and 256 mg betaxolol/kg/day (380 x MRHD), the highest dose was associated with a marked increase in total litter loss within 4 days postpartum. In surviving offspring, growth and development were also affected.
There are no adequate and well-controlled studies in pregnant women. Kerlone (betaxolol hydrochloride) should be used during pregnancy only if the potential benefit justifies the potential risk to the fetus. Beta-blockers reduce placental perfusion, which may result in intrauterine fetal death, immature and premature deliveries. In addition, adverse effects (especially hypoglycemia and bradycardia) may occur in the fetus.
The beta-blocker action persists in the neonate for several days after birth to a treated mother: there is an increased risk of cardiac and pulmonary complications in the neonate in the postnatal period. Bradycardia, respiratory distress and hypoglycemia have also been reported. Accordingly, attentive surveillance of the neonate (heart rate and blood glucose for the first 3 to 5 days of life) in a specialized setting is recommended.
Since Kerlone (betaxolol hydrochloride) is excreted in human milk in sufficient amounts to have pharmacological effects in the infant, caution should be exercised when Kerlone (betaxolol hydrochloride) is administered to a nursing mother.
Safety and effectiveness in pediatric patients have not been established.
Kerlone (betaxolol hydrochloride) may produce bradycardia more frequently in elderly patients. In general, patients 65 years of age and older had a higher incidence rate of bradycardia (heart rate < 50 BPM) than younger patients in U.S. clinical trials. In a double-blind study in Europe, 19 elderly patients (mean age = 82) received betaxolol 20 mg daily. Dosage reduction to 10 mg or discontinuation was required for 6 patients due to bradycardia (See DOSAGE AND ADMINISTRATION).This monograph has been modified to include the generic and brand name in many instances.
Last reviewed on RxList: 7/28/2009
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