SECTRAL

β₁-cardioselectivity has been demonstrated in experimental animal studies. In anesthetized dogs and cats, Sectral 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 Sectral 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 Sectral.

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 Sectral has also been demonstrated on the basis of the following vascular and bronchial effects:

Vascular Effects: Sectral has less antagonistic effects on peripheral vascular β₂-receptors 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 Sectral 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 Sectral induced no significant alteration in the blood lipid profile.

Sectral 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 Sectral 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 Sectral administration with maximal effects occurring between 3 and 8 hours postdosing in normal volunteers. Sectral has demonstrated a significant effect on exercise-induced 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 Sectral has been shown in double-blind controlled studies to be superior to placebo and similar to propranolol and hydrochlorothiazide. In addition, patients responding to Sectral 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 Sectral was compared with placebo, propranolol, and quinidine. Compared with placebo, Sectral significantly reduced mean total ventricular ectopic beats (VEB), paired VEB, multiform VEB, R-on-T beats, and ventricular tachycardia (VT). Both Sectral and propranolol significantly reduced mean total and paired VEB and VT. Sectral and quinidine significantly reduced resting total and complex VEB; the antiarrhythmic efficacy of Sectral was also observed during exercise.

Sectral 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 Sectral and in cats is more cardioselective than Sectral; therefore, this first-pass phenomenon does not attenuate the therapeutic effect of Sectral. Food intake does not have a significant effect on the area under the plasma concentration-time curve (AUC) of Sectral although the rate of absorption and peak concentration decreased slightly.

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

Sectral has a low binding affinity for plasma proteins (about 26%). Sectral 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 Sectral administration. The kinetics of Sectral 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 Sectral, 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). Sectral and its major metabolite are dialyzable.

Sectral crosses the placental barrier and is secreted in breast milk.

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

Sectral is indicated for the management of hypertension in adults. It may be used alone or in combination with other antihypertensive agents, especially thiazide-type diuretics.

Sectral is 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 β-adrenergic receptor blockade may precipitate more severe failure. Although β-blockers should be avoided in overt cardiac failure, Sectral can be used with caution in patients with a history of heart failure who are controlled with digitalis and/or diuretics. Both digitalis and Sectral impair AV conduction. If cardiac failure persists, therapy with Sectral should be withdrawn.

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, Sectral therapy should be withdrawn.

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 Sectral is planned, the patient should be carefully observed, and should be advised to limit physical activity to a minimum while Sectral 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.

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.

PATIENTS WITH BRONCHOSPASTIC DISEASE SHOULD, IN GENERAL, NOT RECEIVE A β-BLOCKER. Because of its relative β₁-selectivity, however, low doses of Sectral 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 Sectral 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.

The necessity, or desirability, of withdrawal of a - blocking therapy prior to major surgery is controversial. -adrenergic receptor blockade impairs the ability of the heart to respond to -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 Sectral. Sectral, like other -blockers, is a competitive inhibitor of -receptor agonists, and its effect on the heart 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

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.

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 Sectral therapy is to be withdrawn should be monitored closely.

Pregnancy Category B: Reproduction studies have been performed with Sectral in rats (up to 630 mg/kg/day) and rabbits (up to 135 mg/kg/day). These doses are equivalent to approximately 31.5 and 6.8 times the maximum recommended therapeutic dose in a 60-kg human, respectively. The compound was not teratogenic in either species. In the rabbit, however, doses of 135 mg/kg/day caused slight fetal growth retardation; this effect was considered to be a result of maternal toxicity, as evidenced by reduced food intake, a lowered rate of body weight gain, and mortality. Studies have also been performed in these species with diacetolol (at doses of up to 450 mg/kg/day in rabbits and up to 1800 mg/kg/day in rats). Other than a significant elevation in postimplantation loss with 450 mg/kg/day diacetolol, a level at which food consumption and body weight gain were reduced in rabbit dams and a nonstatistically significant increase in incidence of bilateral cataract in rat fetuses from dams treated with 1800 mg/kg/day diacetolol, there was no evidence of harm to the fetus. There are no adequate and well-controlled trials in pregnant women. Because animal teratology studies are not always predictive of the human response, Sectral should be used during pregnancy only if the potential benefit justifies the risk to the fetus.

Studies in humans have shown that both acebutolol and diacetolol cross the placenta. Neonates of mothers who have received acebutolol during pregnancy have reduced birth weight, decreased blood pressure, and decreased heart rate. In the newborn the elimination half-life of acebutolol was 6 to 14 hours, while the half-life of diacetolol was 24 to 30 hours for the first 24 hours after birth, followed by a half-life of 12 to 16 hours. Adequate facilities for monitoring these infants at birth should be available.

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

Central Nervous System: Reversible mental depression progressing to catatonia (an acute syndrome characterized by disorientation for time and place), short-term memory loss, emotional lability, slightly clouded sensorium, and decreased performance (neuropsychometrics).

Cardiovascular: Intensification of AV block (see CONTRAINDICATIONS).

Allergic: Erythematous rash, fever combined with aching and sore throat, laryngospasm, and respiratory distress.

Hematologic: Agranulocytosis, nonthrombocytopenic, and thrombocytopenic purpura.

Gastrointestinal: Mesenteric arterial thrombosis and ischemic colitis.

Miscellaneous: Reversible alopecia and Peyronie’s disease. The oculomucocutaneous syndrome associated with the β-blocker practolol has not been reported with Sectral during investigational use and extensive foreign clinical experience.

The initial dosage of Sectral 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 per day, although some patients have been maintained on as little as 200 mg per 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 dose of Sectral 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 per day. If treatment is to be discontinued, the dosage should be reduced gradually over a period of about two weeks.