Carbutol

The management of all grades of hypertension, angina pectoris and the control of tachyarrhythmias.

Hypertension: Initial dosage of 400mg orally once daily at breakfast or 200mg orally twice daily. If response is not adequate within two weeks, dosage may be increased up to 400mg orally twice daily; if the hypertension is still not adequately controlled consideration should be given to adding a second antihypertensive agent such as the calcium antagonist nifedipine or small doses of a thiazide diuretic.

Angina pectoris: Initial dosage of 400mg orally once daily at breakfast or 200mg twice daily. In severe forms up to 300mg three times daily may be required. Up to 1200mg daily has been used.

Cardiac Arrhythmias: When given orally, an initial dose of 200mg is recommended. The daily dose requirement for long term anti arrhythmic activity should lie between 400 and 1200mg daily. The dose can be gauged by response, and better control may be achieved by divided doses rather than single doses. It may take up to three hours for maximal anti-arrhythmic effect to become apparent.

Elderly: There are no specific dosage recommendations for the elderly with normal glomerular filtration rate. Dose reduction is necessary if moderate to severe renal impairment is present

Children: Paediatric dose has not been established.

For all indications, it is advised that the lowest recommended dosage be used initially.

Cardiogenic shock is an absolute contraindication. Extreme caution is required in patients with blood pressures of the order of 100/60 mmHg or below. Carbutol is also contraindicated in patients with second and third degree heart block, sick sinus syndrome, marked bradycardia (< 45-50 bpm), uncontrolled heart failure, metabolic acidosis, severe peripheral circulatory disorders, hypersensitivity to acebutolol, any of the excipients or to beta blockers, and untreated phaeochromocytoma.

Renal impairment is not a contraindication to the use of Carbutol which has both renal and non-renal excretory pathways. Some caution should be exercised when administering high doses to patients with severe renal failure as accumulation could possibly occur in these circumstances.

The dosage frequency should not exceed once daily in patients with renal impairment. As a guide, the dosage should be reduced by 50% when glomerular filtration rates are between 25-50ml/min and by 75% when they are below 25ml/min.

Drug-induced bronchospasm is usually at least partially reversible by the use of a suitable agonist.

Although cardio-selective beta blockers may have less effect on lung function than non-selective beta blockers as with all beta blockers they should be avoided in patients with obstructive airways disease unless there are compelling clinical reasons for their use. Where such reasons exist, cardio-selective β-blockers should be used with the utmost care.

Beta-blockers may induce bradycardia. In such cases, the dosage should be reduced.

They may be used with care in patients with controlled heart failure.

Use with caution in patients with Prinzmetal's angina.

Beta blockers may aggravate peripheral circulatory disorders. They may mask signs of thyrotoxicosis and hypoglycaemia. They should only be used in patients with phaeochromocytoma with concomitant alpha-adrenoceptor therapy.

Patients with known psoriasis should take beta-blockers only after careful consideration.

Beta-blockers may increase both the sensitivity towards allergens and the seriousness of anaphylactic reactions.

Withdrawal of treatment by beta blockers should be achieved by gradual dosage reduction; this is especially important in patients with ischaemic heart disease.

When it has been decided to interrupt beta-blockade prior to surgery, therapy should be discontinued for at least 24 hours. Continuation of therapy reduces the risk of arrhythmias but the risk of hypotension may be increased. If treatment is continued, caution should be observed with the use of certain anaesthetic drugs. The patient may be protected against vagal reactions by intravenous administration of atropine.

No studies on the effects on the ability to drive and use machines have been performed. As with all beta-blockers, dizziness or fatigue may occur occasionally. This should be taken into account when driving or operating machinery.

Adverse reactions associated with acebutolol during controlled clinical trials in patients with hypertension, angina pectoris or arrhythmia (1002 patients exposed to acebutolol) are presented by system organ class and by decreasing order of frequency.

The frequency of the events “anti-nuclear antibody” and “lupus like syndrome” was found from 1440 patients suffering from hypertension, angina pectoris or arrhythmia and exposed to acebutolol in open or double blind studies performed in the United States.

Frequencies are defined as: very common (>1/10), common (>1/100 to <1/10); uncommon (>1/1,000 to <1/100); rare (>1/10,000 to <1/1,000); very rare (<1/10,000).

When the exact frequency of the event was not reported, the frequency category assigned is “not known” (ADRs with *).

Adverse reactions reported from post-marketing experience are also listed. These adverse reactions are derived from spontaneous reports and therefore, the frequency of these adverse reactions is “not known” (cannot be estimated from the available data).

The most frequent and serious adverse reactions of acebutolol are related to the beta-adrenergic blocking activity. The most frequent reported clinical adverse reactions are fatigue and gastrointestinal disorders. Among the most serious adverse reactions are cardiac failure, atrioventricular block and bronchospasm. Abrupt withdrawal as for all beta-blockers may exacerbate angina pectoris and precaution is especially required in patients with ischaemic heart disease.

Reporting of suspected adverse reactions

Reporting suspected adverse reactions after authorisation of the medicinal product is important. It allows continued monitoring of the benefit/risk balance of the medicinal product. Healthcare professionals are asked to report any suspected adverse reactions via the Yellow Card Scheme at: www.mhra.gov.uk/yellowcard

In the event of excessive bradycardia or hypotension, 1mg atropine sulphate administered intravenously should be given without delay. If this is insufficient it should be followed by a slow intravenous injection of isoprenaline (5mcg per minute) with constant monitoring until a response occurs. In severe cases of self-poisoning with circulatory collapse unresponsive to atropine and catecholamines the intravenous injection of glucagon 10-20mg may produce a dramatic improvement. Cardiac pacing may be employed if bradycardia becomes severe.

Judicious use of vasopressors, diazepam, phenytoin, lidocaine, digoxin and bronchodilators should be considered depending on the presentation of the patient. Acebutolol can be removed from blood by haemodialysis. Other symptoms and signs of overdosage include cardiogenic shock, AV block, conduction defects, pulmonary oedema, depressed level of consciousness, bronchospasm, hypoglycaemia and rarely hyperkalaemia.

Pharmacotherapeutic group: Beta Blocking agents; Beta blocking agents, selective, ATC code: C07AB04

Mode of action: Carbutol is a beta adrenoceptor antagonist which is cardioselective, i.e. acts preferentially on beta-1 adrenergic receptors in the heart. Its principal effects are to reduce heart rate especially on exercise and to lower blood pressure in hypertensive subjects. Carbutol and its equally active metabolite, diacetolol have anti-arrhythmic activity, the combined plasma half-life of the active drug and metabolite being 7-10 hours. Both have partial agonist activity (PAA) also known as intrinsic sympathomimetic activity (ISA). This property ensures that some degree of stimulation of beta receptors is maintained. Under conditions of rest, this tends to balance the negative chronotropic and negative inotropic effects. Carbutol blocks the effects of excessive catecholamine stimulation resulting from stress.

After oral administration, acebutolol is rapidly and almost completely absorbed. Absorption appears to be unaffected by the presence of food in the gut. There is rapid formation of a major equiactive metabolite, diacetolol, which possesses a similar pharmacological profile to acebutolol. Peak plasma concentrations of active material (i.e. acebutolol plus diacetolol) are achieved within 2-4 hours and the terminal plasma elimination half-life is around 8-10 hours. Because of biliary excretion and direct transfer across the gut wall from the systemic circulation to the gut lumen, more than 50% of an oral dose of Carbutol is recovered in the faeces with acebutolol and diacetolol in equal proportions; the rest of the dose is recovered in the urine, mainly as diacetolol. Both acebutolol and diacetolol are hydrophilic and exhibit poor penetration of the CNS.

No particulars.

Not applicable

No special requirements