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Atenolol

 

ACTIONS

APO-ATENOL (atenolol) is a beta-adrenergic receptor blocking agent with predominant blocking effect on beta-receptors. It does not possess membrane stabilizing or intrinsic sympathommetic (partial agonist) activities.

 

The mechanism of this antihypertensive effect has not been established. Among the factors that may be involved are

 

a) competitive ability to antagonize catecholamine induced tachycardia at the beta-receptor sites in the heart thus decreasing cardiac output :

b) inhibition of renin release by the kidneys.

c) inhibition of the vasomotor centers.

 

The mechanism of the anti-anginal effects is also uncertain. An important factor may be the reduction of myocardial oxygen requirements by blocking catecholamine-induced increases in heart rate, systolic blood pressure and the velocity and extent of myocardial contraction.

 

PHARMACOKINETICS

Approximately 50 percent of an oral dose of atenolol is absorbed from the gastrointestinal tract the remainder being excreted unchanged in the feces. 6 to 16 percent of atenolol is bound to plasma protein. Maximum plasma concentrations are reached within 2-4 hours. The mean peak plasma concentrations of atenolol were approximately 300 and 700 nanogram/mL following administration of 50 and 100 mg respectively. The plasma half-life is approximately 6-7 hours. Atenolol is extensively distributed to extravascular tissues but only a small amount is found in the central nervous system.

 

Approximately 10 percent of atenolol is metabolized in man. About 3 percent of the material recovered in the urine was the hydroxylated metabolite which has been shown in animal studies to have 10 percent of the pharmacological activity of atenolol. Approximately 47 and 53 percent of the oral dose is eliminated in the urine and feces, respectively. Recovery is complete after 72 hours.

 

A comparative bioavailability study was performed using normal human volunteers. The rate and extent of absorption after a single oral 100 mg dose of Tenormin 100 mg or Apo-Atenol 100 mg was measured and compared. The results can be summarized as follows :

 

  Tenormin 100 mg Apo-Atenol 100 mg %
AUC 0.48 ( ng-hr/mL ) 6202.1 5781.8 6.8
Cmax ( ng/mL ) 697.3 660.8 5.3
Tmax ( hr ) 2.5 3.3 32
t ( hr ) 7.1 7.0 1.4

 

INDICATIONS

Hypertension : APO-ATENOL (atenolol) is indicted in patients with mild or moderate hypertension. It is usually used in combination with other drugs, particularly a thiazide diuretic. However, it may be tried alone as an initial agent in those patients in whom, in the judgment of the physician. Treatment should be started with diuretics and/or vasodilators to treat severe hypertension.

 

The combination of atenolol with a diuretic or peripheral vasodilator has been found to be compatible. Limited experience with other antihypertensive agents has not shown evidence of incompatibility with atenolol. Therefore abrupt withdrawal of atenolol may be followed by an exacerbation of the symptoms of hyperthyroidism, including thyroid storm.

 

PRECAUTIONS

a) Because of its predominantly beta-block effect APO-Atenol (atenolol) may be tried in patients with diseases associated with bronchospasm who require beta-blocker therapy. However, careful monitoring of such patients is mandatory and a bronchodilator must be administered concomitantly. If initial bronchodilator therapy is being contemplated a sympathomimetic brondilator might be considered. in patients already on bronchodilator therapy, the dose may have to be increased if necessary. Despite these precautions, the respiratory status of some patients may worsen, and in such cases, atenolol should be withdrawn.

 

b) There may be increased difficulty in treating an allergic type reaction in patients on beta-blockers. In these patients, the reaction may be more severe due to pharmacological effects of beta-blockers and problems with fluid-changes. Epinephrine should be administered with caution since it may not have its usual effects in the treatment of anaphylaxis. On the one hand, large dosages of epinephrine may be needed to overcome the bronchospasm, while on the other, these dosages can be associated with excessive alpha adrenergic stimulation with consequent hypertension, reflex bradycardia and heart-block and possible potentiation of bronchospsasm. Alternatives to the use of large doses of epinephrine include vigorous supportive care such as fluids and the use of beta agonists including parenteral salbutamol or isoproterenol to overcome bronchospasm and norepinephrine to overcome hypotension.

 

c) Atenolol should be administered with caution to patients subject to spontaneous hypoglycemia, or to diabetic patients (especially those with labile diabetes) who are receiving insulin or oral hypoglycemic agents. Beta-adrenergic blockers may mask the premonitory signs and symptoms of acute hypoglycemia.

 

d) Animal Studies : Chronic studies performed in animals have revealed the occurrence of vacuolation of epithelial cells of Brunner's glands in the duodenum of both male and female dogs at all tested dose levels of atenolol (starting at 15 mg/kg/day or 7.5 times the maximum recommended human dose) and an increased incidence of atrial degeneration of hearts of male rats at 300 but not 150 mg/atenolol/kg/day (150 and 75 times the maximum recommended human dose, respectively).

 

e) Appropriate laboratory tests for monitoring renal, hepatic and hematoporetic function should be performed at regular intervals during long-term treatment.

 

Atenolol is not recommended for the emergency treatment of hypertensive crises.

 

Angina Pectoris: Atenolol is indicated in the long-term management of patients with angina pectoris due to ischemic heart disease.

 

CONTRAINDICATIONS

APO-ATENOLOL (atenolol) should not be used in the presence of

1. sinus bradycardia

2. second and third degree A-V block

3. right ventricular failure secondary to pulmonary hypertension

4. Congestive heart failure

5. Cardiogenic shock

6. Anesthesia with agents that produce myocardial depression, e.g ether

7. Hypersensitivity to atenolol.

 

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