Acebutolol Hydrochloride

β₁-cardioselectivity has been demonstrated in experimental animal studies. In anesthetized dogs and cats, acebutolol is more potent in antagonizing isoproterenol-induced tachycardia (β₁) than in antagonizing isoproterenol-induced vasodilatation (β₂). In guinea pigs and cats, it is more potent in antagonizing this tachycardia than in antagonizing isoproterenol-induced bronchodilatation (β₂). ISA of acebutolol has been demonstrated in catecholamine-depleted rats by tachycardia induced by intravenous administration of this agent. A membrane-stabilizing effect has been detected in animals, but only with high concentrations of acebutolol. Clinical studies have demonstrated β₁-blocking activity at the recommended doses by: a) reduction in the resting heart rate and decrease in exercise-induced tachycardia; b) reduction in cardiac output at rest and after exercise; c) reduction of systolic and diastolic blood pressures at rest and postexercise; d) inhibition of isoproterenol-induced tachycardia.

The β₁-selectivity of acebutolol has also been demonstrated on the basis of the following vascular and bronchial effects:

Acebutolol is well absorbed from the GI tract. It is subject to extensive first-pass hepatic biotransformation, with an absolute bioavailability of approximately 40% for the parent compound. The major metabolite, an N-acetyl derivative (diacetolol), is pharmacologically active. This metabolite is equipotent to acebutolol and in cats is more cardioselective than acebutolol; therefore, this first-pass phenomenon does not attenuate the therapeutic effect of acebutolol. Food intake does not have a significant effect on the area under the plasma concentration-time curve (AUC) of acebutolol although the rate of absorption and peak concentration decreased slightly.

The plasma elimination half-life of acebutolol is approximately 3 to 4 hours, while that of its metabolite, diacetolol, is 8 to 13 hours. The time to reach peak concentration for acebutolol is 2.5 hours and for diacetolol, after oral administration of acebutolol hydrochloride, 3.5 hours.

Within the single oral dose range of 200 mg to 400 mg, the kinetics are dose proportional. However, this linearity is not seen at higher doses, probably due to saturation of hepatic biotransformation sites. In addition, after multiple dosing the lack of linearity is also seen by AUC increases of approximately 100% as compared to single oral dosing. Elimination via renal excretion is approximately 30% to 40% and by non-renal mechanisms 50% to 60%, which includes excretion into the bile and direct passage through the intestinal wall.

Acebutolol hydrochloride has a low binding affinity for plasma proteins (about 26%). Acebutolol and its metabolite, diacetolol, are relatively hydrophilic and, therefore, only minimal quantities have been detected in the cerebrospinal fluid (CSF).

Drug interaction studies with tolbutamide and warfarin indicated no influence on the therapeutic effects of these compounds. Digoxin and hydrochlorothiazide plasma levels were not affected by concomitant acebutolol administration. The kinetics of acebutolol were not significantly altered by concomitant administration of hydrochlorothiazide, hydralazine, sulfinpyrazone, or oral contraceptives.

In patients with renal impairment, there is no effect on the elimination half-life of acebutolol, but there is decreased elimination of the metabolite, diacetolol, resulting in a 2- to 3-fold increase in its half-life. For this reason, the drug should be administered with caution in patients with renal insufficiency (see PRECAUTIONS). Acebutolol and its major metabolite are dialyzable.

Acebutolol crosses the placental barrier, and is secreted in breast milk.

In geriatric patients, the bioavailability of acebutolol and its metabolite is increased, approximately 2-fold, probably due to decreases in the first-pass metabolism and renal function in the elderly.

Acebutolol hydrochloride capsules are indicated for the management of hypertension in adults. They may be used alone or in combination with other antihypertensive agents, especially thiazide-type diuretics.

Acebutolol hydrochloride capsules are indicated in the management of ventricular premature beats; it reduces the total number of premature beats, as well as the number of paired and multiform ventricular ectopic beats, and R-on-T beats.

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 failure. Although beta-blockers should be avoided in overt cardiac failure, acebutolol can be used with caution in patients with a history of heart failure who are controlled with digitalis and/or diuretics. Both digitalis and acebutolol impair AV conduction. If cardiac failure persists, therapy with acebutolol should be withdrawn.

In patients with aortic or mitral valve disease or compromised left ventricular function, continued depression of the myocardium with beta-blocking agents over a period of time may lead to cardiac failure. At the first signs of failure, patients should be digitalized and/or be given a diuretic and the response observed closely. If cardiac failure continues despite adequate digitalization and/or diuretic, acebutolol therapy should be withdrawn.

Following abrupt cessation of therapy with certain beta-blocking agents in patients with coronary artery disease, exacerbation of angina pectoris and, in some cases, myocardial infarction and death have been reported. Therefore, such patients should be cautioned against interruption of therapy without a physician's advice. Even in the absence of overt ischemic heart disease, when discontinuation of acebutolol is planned, the patient should be carefully observed, and should be advised to limit physical activity to a minimum while acebutolol is gradually withdrawn over a period of about 2 weeks. (If therapy with an alternative beta-blocker is desired, the patient may be transferred directly to comparable doses of another agent without interruption of beta-blocking therapy.) If an exacerbation of angina pectoris occurs, antianginal therapy should be restarted immediately in full doses and the patient hospitalized until his condition stabilizes.

Treatment with beta-antagonists reduces cardiac output and can precipitate or aggravate the symptoms of arterial insufficiency in patients with peripheral or mesenteric vascular disease. Caution should be exercised with such patients, and they should be observed closely for evidence of progression of arterial obstruction.

PATIENTS WITH BRONCHOSPASTIC DISEASE SHOULD, IN GENERAL, NOT RECEIVE A BETA-BLOCKER. Because of its relative β₁-selectivity, however, low doses of acebutolol may be used with caution in patients with bronchospastic disease who do not respond to, or who cannot tolerate, alternative treatment. Since β₁-selectivity is not absolute and is dose dependent, the lowest possible dose of acebutolol should be used initially, preferably in divided doses to avoid the higher plasma levels associated with the longer dose-interval. A bronchodilator, such as a theophylline or a β₂-stimulant, should be made available in advance with instructions concerning its use.

Chronically administered beta-blocking therapy should not be routinely withdrawn prior to major surgery; however, the impaired ability of the heart to respond to reflex adrenergic stimuli may augment the risks of general anesthesia and surgical procedures.

Beta-blockers may potentiate insulin-induced hypoglycemia and mask some of its manifestations such as tachycardia; however, dizziness and sweating are usually not significantly affected. Diabetic patients should be warned of the possibility of masked hypoglycemia.

Beta-adrenergic blockade may mask certain clinical signs (tachycardia) of hyperthyroidism. Abrupt withdrawal of beta-blockade may precipitate a thyroid storm; therefore, patients suspected of developing thyrotoxicosis from whom acebutolol therapy is to be withdrawn should be monitored closely.

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

Studies on the effect of acebutolol in patients with renal insufficiency have not been performed in the United States. Foreign published experience shows that acebutolol has been used successfully in chronic renal insufficiency. Acebutolol is excreted through the G.I. tract, but the active metabolite, diacetolol, is eliminated predominantly by the kidney. There is a linear relationship between renal clearance of diacetolol and creatinine clearance. Therefore, the daily dose of acebutolol should be reduced by 50% when the creatinine clearance is less than 50 mL/min and by 75% when it is less than 25 mL/min. Acebutolol should be used cautiously in patients with impaired hepatic function.

Acebutolol has been used successfully and without problems in elderly patients in the U.S. clinical trials without specific adjustment of dosage. However, elderly patients may require lower maintenance doses because the bioavailability of both acebutolol and its metabolite are approximately doubled in this age group.

Patients, especially those with evidence of coronary artery disease, should be warned against interruption or discontinuation of acebutolol therapy without a physician's supervision. Although cardiac failure rarely occurs in properly selected patients, those being treated with beta-adrenergic blocking agents should be advised to consult a physician if they develop signs or symptoms suggestive of impending CHF, or unexplained respiratory symptoms.

Patients should also be warned of possible severe hypertensive reactions from concomitant use of alpha-adrenergic stimulants, such as the nasal decongestants commonly used in OTC cold preparations and nasal drops.

Acebutolol, like other beta-blockers, has been associated with the development of antinuclear antibodies (ANA). In prospective clinical trials, patients receiving acebutolol had a dose-dependent increase in the development of positive ANA titers and the overall incidence was higher than that observed with propranolol. Symptoms (generally persistent arthralgias and myalgias) related to this laboratory abnormality were infrequent (less than 1% with both drugs). Symptoms and ANA titers were reversible upon discontinuation of treatment.

Catecholamine-depleting drugs, such as reserpine, may have an additive effect when given with beta-blocking agents. Patients treated with acebutolol plus catecholamine depletors should, therefore, be observed closely for evidence of marked bradycardia or hypotension which may present as vertigo, syncope/presyncope, or orthostatic changes in blood pressure without compensatory tachycardia. Exaggerated hypertensive responses have been reported from the combined use of beta-adrenergic antagonists and alpha-adrenergic stimulants, including those contained in proprietary cold remedies and vasoconstrictive nasal drops. Patients receiving beta-blockers should be warned of this potential hazard.

Blunting of the antihypertensive effect of beta-adrenoceptor blocking agents by non-steroidal anti-inflammatory drugs has been reported. No significant interactions with digoxin, hydrochlorothiazide, hydralazine, sulfinpyrazone, oral contraceptives, tolbutamide, or warfarin have been observed.

Both digitalis glycosides and beta-blockers slow atrioventricular conduction and decrease heart rate. Concomitant use can increase the risk of bradycardia.

Chronic oral toxicity studies in rats and mice, employing dose levels as high as 300 mg/kg/day, which is equivalent to 15 times the maximum recommended (60 kg) human dose, did not indicate a carcinogenic potential for acebutolol. Diacetolol, the major metabolite of acebutolol in man, was without carcinogenic potential in rats when tested at doses as high as 1800 mg/kg/day. Acebutolol and diacetolol were also shown to be devoid of mutagenic potential in the Ames Test. Acebutolol, administered orally to two generations of male and female rats at doses of up to 240 mg/kg/day (equivalent to 12 times the maximum recommended therapeutic dose in a 60-kg human) and diacetolol, administered to two generations of male and female rats at doses of up to 1000 mg/kg/day, had no significant impact on reproductive performance or fertility.

The effect of acebutolol on labor and delivery in pregnant women is unknown. Studies in animals have not shown any effect of acebutolol on the usual course of labor and delivery.

Acebutolol and diacetolol also appear in breast milk with a milk:plasma ratio of 7.1 and 12.2, respectively. Use in nursing mothers is not recommended.

Safety and effectiveness in pediatric patients have not been established.

Clinical studies of acebutolol and other reported clinical experience is inadequate to determine whether there are differences in safety or effectiveness between patients above or below age 65. Elderly subjects evidence greater bioavailability of acebutolol (see CLINICAL PHARMACOLOGY: Pharmacokinetics and Metabolism), presumably because of age-related reduction in first-pass metabolism and renal function. Therefore, it may be appropriate to start elderly patients at the low end of the dosing range (see DOSAGE AND ADMINISTRATION: Use in Older Patients).

In addition, certain adverse effects not listed above have been reported with other beta-blocking agents and should also be considered as potential adverse effects of acebutolol.

The initial dosage of acebutolol hydrochloride capsules in uncomplicated mild-to-moderate hypertension is 400 mg. This can be given as a single daily dose, but in occasional patients twice daily dosing may be required for adequate 24-hour blood-pressure control. An optimal response is usually achieved with dosages of 400 to 800 mg/day, although some patients have been maintained on as little as 200 mg/day. Patients with more severe hypertension or who have demonstrated inadequate control may respond to a total of 1200 mg daily (administered b.i.d.), or to the addition of a second antihypertensive agent. Beta-1 selectivity diminishes as dosage is increased.

The usual initial dosage of acebutolol hydrochloride capsules is 400 mg daily given as 200 mg b.i.d. Dosage should be increased gradually until an optimal clinical response is obtained, generally at 600 to 1200 mg/day. If treatment is to be discontinued, the dosage should be reduced gradually over a period of about 2 weeks.

Older patients have an approximately 2-fold increase in bioavailability and may require lower maintenance doses. Doses above 800 mg/day should be avoided in the elderly.