Acebutolol Hydrochloride

ACEBUTOLOL HYDROCHLORIDE — acebutolol hydrochloride capsule
Physicians Total Care, Inc.

DESCRIPTION

Acebutolol HCl is a selective, hydrophilic beta-adrenoreceptor blocking agent with mild intrinsic sympathomimetic activity for use in treating patients with hypertension and ventricular arrhythmias. It is marketed in capsule form for oral administration. Acebutolol HCl capsules are provided in two dosage strengths which contain 200 or 400 mg of acebutolol as the hydrochloride salt. The inactive ingredients present are D&C Red 28, D&C Yellow 10, FD&C Blue 1, FD&C Red 40, gelatin, maize starch, povidone, titanium dioxide and stearic acid.

Acebutolol HCl has the following structural formula:

f1931f84-figure-01
(click image for full-size original)

C18 H28 N2 O4 •HCl M.W. 372.89

Acebutolol HCl is a white or slightly off-white powder freely soluble in water, and less soluble in alcohol. Chemically it is defined as the hydrochloride salt of (±) N-[3-Acetyl-4-[2-hydroxy-3-[(1-methylethyl) amino]propoxy]phenyl] butanamide.

CLINICAL PHARMACOLOGY

Acebutolol is a cardioselective, β-adrenoreceptor blocking agent, which possesses mild intrinsic sympathomimetic activity (ISA) in its therapeutically effective dose range.

PHARMACODYNAMICS

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 isoproterenolinduced 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 exerciseinduced 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:

Vascular Effects: Acebutolol has less antagonistic effects on peripheral vascular β2receptors at rest and after epinephrine stimulation than nonselective β-antagonists.

Bronchial Effects: In single-dose studies in asthmatics examining effects of various beta-blockers on pulmonary function, low doses of acebutolol produce less evidence of bronchoconstriction and less reduction of beta2 agonist, bronchodilating effects, than nonselective agents like propranolol but more than atenolol.

ISA has been observed with acebutolol in man, as shown by a slightly smaller (about 3 beats per minute) decrease in resting heart rate when compared to equivalent β-blocking doses of propranolol, metoprolol or atenolol. Chronic therapy with acebutolol induced no significant alteration in the blood lipid profile.

Acebutolol has been shown to delay AV conduction time and to increase the refractoriness of the AV node without significantly affecting sinus node recovery time, atrial refractory period, or the HV conduction time. The membrane-stabilizing effect of acebutolol is not manifest at the doses used clinically.

Significant reductions in resting and exercise heart rates and systolic blood pressures have been observed 1.5 hours after acebutolol administration with maximal effects occurring between 3 and 8 hours postdosing in normal volunteers. Acebutolol has demonstrated a significant effect on exerciseinduced tachycardia 24 to 30 hours after drug administration.

There are significant correlations between plasma levels of acebutolol and both the reduction in resting heart rate and the percent of β-blockade of exercise-induced tachycardia.

The antihypertensive effect of acebutolol has been shown in double-blind controlled studies to be superior to placebo and similar to propranolol and hydrochlorothiazide. In addition, patients responding to acebutolol administered twice daily had a similar response whether the dosage regimen was changed to once daily administration or continued on a b.i.d. regimen.

Most patients responded to 400 to 800 mg per day in divided doses.

The antiarrhythmic effect of acebutolol was compared with placebo, propranolol, and quinidine. Compared with placebo, acebutolol significantly reduced mean total ventricular ectopic beats (VEB), paired VEB, multiform VEB, R-on-T beats, and ventricular tachycardia (VT). Both acebutolol and propranolol significantly reduced mean total and paired VEB and VT.

Acebutolol and quinidine significantly reduced resting total and complex VEB; the antiarrhythmic efficacy of acebutolol was also observed during exercise.

PHARMACOKINETICS and METABOLISM

Acebutolol is well absorbed from the GI tract. It is subject to extensive firstpass hepatic biotransformation, with an absolute bioavailability of approximately 40% for the parent compound. The major metabolite, an Nacetyl 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, 3.5 hours.

Within the single oral dose range of 200 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 nonrenal mechanisms 50% to 60%, which includes excretion into the bile and direct passage through the intestinal wall.

Acebutolol 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 two- to three-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 two-fold, probably due to decreases in the first-pass metabolism and renal function in the elderly.

INDICATIONS & USAGE

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

VENTRICULAR ARRHYTHMIAS: 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.

CONTRAINDICATIONS

Acebutolol HCl is contraindicated in: 1) persistently severe bradycardia; 2) second-and third-degree hear t block; 3) over t cardiac failure; and 4) cardiogenic shock. (See Warnings.)

WARNINGS

CARDIAC FAILURE: Sympathetic stimulation may be essential for support of the circulation in individuals with diminished myocardial contractility, and its inhibition by β-adrenergic receptor blockade may precipitate more severe failure. Although β-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 PATIENTSWITHOUT A HISTORY OF CARDIAC FAILURE: In patients with aortic or mitral valve disease or compromised left ventricular function, continued depression of the myocardium with β-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.

EXACERBATION OF ISCHEMIC HEART DISEASE FOLLOWING ABRUPT WITHDRAWAL: Following abrupt cessation of therapy with certain β-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 two weeks. (If therapy with an alternative β-blocker is desired, the patient may be transferred directly to comparable doses of another agent without interruption of β-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.

PERIPHERAL VASCULAR DISEASE: Treatment with β-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.

BRONCHOSPASTIC DISEASES: PATIENTS WITH BRONCHOSPASTIC DISEASE SHOULD, IN GENERAL, NOT RECEIVE A β-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 theophylline or a β2-stimulant, should be made available in advance with instructions concerning its use.

ANESTHESIA AND MAJOR SURGERY: The necessity, or desirability, of withdrawal of a β-blocking therapy prior to major surgery is controversial. β-adrenergic receptor blockade impairs the ability of the heart to respond to β-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 enhanced 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 trichlorethylene, and it is prudent to use the lowest possible dose of acebutolol.

Acebutolol, like other β-blockers, is a competitive inhibitor of β-receptor agonists, and its effect on the hear t can be reversed by cautious administration of such agents (e.g., dobutamine or isoproterenol – see Overdosage).

Manifestations of excessive vagal tone (e.g., profound bradycardia, hypotension) may be corrected with atropine 1 to 3 mg IV in divided doses.

DIABETES AND HYPOGLYCEMIA: β-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.

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

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