COMPOSITION: Each tablet contains 50 or 100 mg Atenolol
PHARMACOLOGICAL CLASSIFICATION: A 5.2 Adrenolytics (Sympatholytics).
PHARMACOLOGICAL ACTION: Venapulse (Atenolol) is a cardioselective ß1-adrenergic blocking agent, with insignificant partial agonist activity and weak membrane-stabilizing properties. It is incompletely absorbed when administered orally and is excreted largely unchanged in the urine. Venapulse has a half-life in plasma of approximately 6 to 8 hours. As Venapulse is highly hydrophilic it does not readily cross the blood-brain barrier.
INDICATIONS: Venapulse is used in the management of angina pectoris and hypertension.
CONTRA INDICATIONS: Venapulse should not be given to patients with partial heart block, and should never be given to patients with phaeochromocytoma without concomitant alpha-adrenoceptor blocking therapy. It should not be given together with verapamil or within several days of discontinuing treatment and vice versa.
Venapulse is contra-indicated in patients with bronchial asthma, bronchitis, bronchospasm or chronic respiratory diseases, metabolic acidosis, atrioventricular block, marked bradycardia, (less than 50 per minute), heart failure refractory to digitalis, uraemia, pregnancy, lactation, hypoglycaemia, second and third degree heart block, peripheral vascular diseases and Raynaud's phenomenon.
The normal dose should be reduced in elderly patients, or in patients suffering from renal dysfunction.
It is contra-indicated in patients with metabolic acidosis and after prolonged fasting.
In the peri-operative period, it is generally unwise to reduce the dosage to that which the patient is accustomed, as there may be danger of aggravation of angina pectoris or of hypertension. A patient's normal tachycardiac response to hypovolaemia or blood loss may be obscured during or after surgery. Particular caution should be taken in this regard.
WARNING. Venapulse should be given to patients with congestive heart failure only when they are fully digitalised and only then with great caution. Great care should be exercised in giving Venapulse to patients undergoing general anaesthesia, and myocardial depressants, such as chloroform and ether must be avoided.
DOSAGE AND DIRECTIONS FOR USE:
Angina Pectoris The usual dose is 100 mg daily, given as single or divided doses. It is unlikely that additional benefit will be obtained by increasing the dose. Hypertension The usual dose is 100 mg daily, as a single dose. It is unlikely that additional benefit will be obtained by increasing the dose.
The dosage should be decreased in patients with severe impairment of renal function.
Caution should be exercised when transferring a patient from clonidine. The withdrawal of clonidine may result in the release of large amounts of catecholamines which may give rise to a hypertensive crisis.
If beta-blockers are administered in these circumstances, the unopposed alpha-receptor stimulation may potentiate this effect.
SIDE-EFFECTS AND SPECIAL PRECAUTIONS:
Side-effects The most common side-effects of atenolol are nausea, vomiting and other gastro-intestinal disturbances, fatigue and dizziness. Cardiovascular effects include bradycardia, hypotension, or paradoxical hypertension, cold extremities and Raynaud's phenomenon: congestive heart failure or heart block may be precipitated. Central nervous system effects include depression, hallucinations, confusion, psychotic episodes, and disturbances of sleep and vision. Paraesthesia and loss of hearing have been reported. Bronchospasm may occur, particularly in susceptible individuals. Blood disorders and skin rashes may also occur. Other adverse effects reported include impaired sexual function, allergic reactions, metabolic disturbances, fluid retention and weight gain, alopecia, myopathies, dry eyes, and stomatitis.
Side-effects may be minimised by starting treatment with a small dose and gradually increasing, although serious reactions have been reported after small doses. Special precautions: Atenolol may mask the symptoms of hyperthyroidism. It may also mask the symptoms of hypoglycaemia, as well as enhancing the effects of hypoglycaemic agents in patients with diabetes mellitus. Important: Digitalisation of patients receiving long-term ß-blocker therapy may be necessary if congestive heart failure is likely to develop. This combination can be considered despite the potentiation of the negative chronotropic effects of the two medicines. Careful control of dosages and of the individual patient's response (and notably pulse-rate) is essential in this situation.
Abrupt discontinuation of therapy may cause exacerbation of angina pectoris in patients suffering from ischaemic heart disease. Discontinuation of therapy should be gradual and patients should be advised to limit the extent of their physical activity during the period that the medicine is being discontinued.
Administration to pregnant mothers shortly before giving birth, or during labour may result in the newborn infants being born hypotonic, collapsed and hypoglycaemic.
Venapulse should not be administered to patients with phaeochromocytoma without concurrent alpha-adrenergic blocking therapy. If Venapulse and clonidine are given concurrently the clonidine should not be discontinued until several days after withdrawal of the beta-blocker as severe rebound hypertension may occur.
INTERACTIONS: The effects of other myocardial depressant agents, including anti-arrhythmics such as quinidine, procainamide, or lignocaine, phenytoin, and medicines which interfere with calcium transport, such as verapamil, may also be enhanced by atenolol.
The effects of atenolol are diminished by beta-adrenoceptor stimulating agents such as isoprenaline; the hypotensive effects of atenolol may be dangerously reversed and the peripheral vasoconstrictor effects enhanced by alpha-adrenoceptor stimulating agents such as noradrenaline or those with mixed alpha- and beta-adrenoceptor stimulating properties such as adrenaline; bradycardia may also occur.
The effects of atenolol may be enhanced by adrenergic neurone blocking agents such as guanethidine or bethanidine, or catecholamine-depleting agents such as reserpine and the hypotensive effects by diuretics. Atenolol may enhance some of the cardiac effects of digitalis and diminish others. It has been suggested that clonidine withdrawal symptoms may be exacerbated in patients who are concurrently taking a beta blocker. Please note: Such interactions can have life-threatening consequences.
KNOWN SYMPTOMS OF OVERDOSAGE AND PARTICULARS OF ITS TREATMENT: Overdosage with atenolol may produce bradycardia and severe hypotension. Bronchospasm and heart failure may be produced in certain individuals.
Cases of mild overdose should be observed for at least 4 hours, as apnoea and cardiovascular collapse may appear suddenly.
Gastric lavage should be performed if within 4 hours of suspected overdose. Repeated activated charcoal is necessary in severe overdosage.
Atropine may be used to treat bradycardia. If the response is inadequate, glucagon may be given intravenously. Alternatively, dobutamine or isoprenaline may be used for the management of hypotension. Large doses of isoprenaline may be required to counteract the beta-blockade. Transvenous cardiac pacing may be required for severe bradycardia. Bronchospasm should be treated with IV aminophylline or inhaled, or IV beta-agonist, eg salbutamol.
50 mg tablet:
A white, film coated, biconvex tablet.
100 mg tablet:
An orange-red, film coated, biconvex tablet, bisected on one side.
PRESENTATION: Securitainers of 28 tablets.
STORAGE INSTRUCTIONS: Store below 25°C. Protect from light. KEEP OUT OF REACH OF CHILDREN
50 mg tablets:
100 mg tablets:
NAME AND BUSINESS ADDRESS OF APPLICANT: Pharmacare Limited, 7 Fairclough Road, PORT ELIZABETH 6001
DATE OF PUBLICATION OF THIS PACKAGE INSERT: 14/09/1993
KOHLER C&P P.E.