Betaxolol

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Abstract
Betaxolol1 is a relatively cardioselective β-adrenoceptor blocking drug, with no partial agonist (intrinsic sympathomimetic) activity and weak membrane-stabilising (local anaesthetic) activity. Its pharmacokinetic properties of most interest include high bioavailability after oral administration, and a long elimination half-life. It has a narrow dose-response range, which obviates the need for dose titration, with 10 to 20mg once daily being the usual dosage. This dose reduces systolic and diastolic blood pressures by about 15mm Hg in most patients with mild to moderate hypertension. In a few comparative studies betaxolol 20mg daily was as effective as atenolol and moderate doses of propranolol, and more effective than acebutolol, in reducing blood pressure in such patients. Betaxolol has been well tolerated in most patients. Thus, betaxolol is an effective alternative to other β-blocking drugs in patients with essential hypertension, with properties that may offer advantages in some patients. Betaxolol is a relatively cardioselective β-adrenoceptor blocking drug which has no partial agonist activity and very little membrane-stabilising activity (based on standard animal models). Its β-blocking potency in animal and human studies was about 4 times that of propranolol after oral administration. It has a long duration of action, with a significant reduction in exercise-induced tachycardia being observed in healthy subjects 48 hours after the administration of a single 40mg dose. Resting heart rate was also reduced by betaxolol (by about 15 to 30%) in both healthy subjects and in patients with cardiovascular disorders. Both systolic and diastolic blood pressures are reduced by betaxolol, as is myocardial oxygen demand. In subjects with normal renal function, betaxolol did not alter glomerular filtration rate, but produced a small increase in renal blood flow. Its effects on sodium and potassium excretion varied between studies, and need further clarification. Respiratory function of normal subjects was not affected by betaxolol, while that of subjects with airways disease was less affected by betaxolol than by propranolol. In non-diabetic healthy subjects or patients with cardiovascular disease, betaxolol did not affect either glucose metabolism, the reduction in blood pressure produced by insulin, or the time taken to recover from hypoglycaemia (unlike propranolol which prolonged recovery time). Similarly, insulin-induced tachycardia, was minimally affected by betaxolol (but was reduced by propranolol). However, the effects produced by betaxolol on insulin-induced changes in free fatty acid and glycerol serum concentrations were similar to those produced by propranolol. Mean total cholesterol and triglyceride serum concentrations were unchanged or increased only slightly during long term treatment with betaxolol. There was no change in apoprotein B concentrations and no reduction in HDL cholesterol. Betaxolol is very lipid soluble but does not undergo extensive first-pass metabolism. Bioavailability after oral administration is about 80 to 89%, and is unaffected by the presence of food in the gut. Peak plasma concentrations after betaxolol show less interindividual variability than after propranolol. Betaxolol is distributed widely, including to the placenta and into milk (where levels are about 3 times higher than in blood). Little protein binding (about 50%) occurs. Betaxolol is metabolised into mainly inactive metabolites which are excreted in the urine; some unchanged drug (about 15% of a dose) is also excreted in the urine. Betaxolol’s elimination half-life is long (14 to 22 hours), and is increased by severe renal impairment but is not affected by hepatic dysfunction. Its half-life is also increased in elderly subjects and in day-old infants. Otherwise, its pharmacokinetic behaviour is largely the same in children as in adults. Several short term and limited longer term open studies have been carried out to assess the antihypertensive effect of betaxolol. These studies indicated that 20mg daily was the optimum dose in most patients with moderate hypertension. Placebo-controlled studies have generally been of short duration. Blood pressure was well-controlled by a single daily dose of betaxolol, again with most patients responding to 20 mg/day. The betaxolol-induced reduction in blood pressure (about 15mm Hg in these patients with mild to moderate hypertension) was significantly greater than that produced by placebo. Betaxolol’s antihypertensive effect has also been compared with that produced by other β-blockers. In a few comparative studies, betaxolol (20mg once a day) was as effective as a moderate dose of propranolol (160mg daily) and atenolol (100 to 200mg once a day) in reducing blood pressure, and was more effective than acebutolol (400mg once a day). At the end of a 7-week study, 62% of patients given betaxolol and 31% of those given acebutolol had a diastolic blood pressure of less than 90mm Hg. Increasing the dose of betaxolol from 20 to 40 mg/day did not increase its antihypertensive effect in most patients but did produce a greater reduction in heart rate. Betaxolol has been well tolerated by most patients, but long term experience (more than a year) is limited to relatively small numbers of patients. There have been a few reports of severe bradycardia, usually in elderly patients or in patients given a high dose (40 mg/day). Only a few cases of bronchoconstriction have been reported. Mild central effects, such as tiredness and headaches, were the most commonly reported adverse reactions. No hallucinations or nightmares have been reported. Peripheral circulation may have been affected in some patients since there have been reports of cold, numb hands and feet, paraesthesia, and Raynaud’s phenomenon. Gastrointestinal disturbance has also occurred in some patients; nausea, discomfort and constipation have all been reported. On longer term administration (up to 6 months), side effects necessitated discontinuation of treatment in about 7% of patients, while about 85% of patients treated for 3 to 6 months did not report any side effects. The recommended starting dosage for mild to moderate hypertension is 10 to 20 mg/day in a single oral dose. A higher dose may be given if necessary but this is more likely to produce an unwanted reduction in heart rate than to reduce elevated blood pressure to a much greater extent. A dose of 10 mg/day should be used in the elderly and in patients with severe renal disease. Dose modification is generally unnecessary in patients with mild to moderate renal insufficiency or hepatic disease.