Blokiuret

Management of hypertension.

Posology

Adults

One tablet daily. Most patients with hypertension will give a satisfactory response to a single tablet daily of Blokiuret. There is little or no further fall in blood pressure with increased dosage and, where necessary, another antihypertensive drug, such as a vasodilator, can be added.

Elderly

Dosage requirements are often lower in this age group.

Paediatric population

The use of Blokiuret is not recommended in children. The safety and efficacy of Blokiuret in children has not yet been established.

Renal Impairment

Due to the properties of the chlortalidone component, Blokiuret tablets has reduced efficacy in the presence of renal insufficiency. This fixed dose combination should thus not be administrated to patients with severe renal impairment.

Method of administration

Blokiuret 100 mg/25 mg film-coated tablets are administered orally.

Blokiuret tablets should not be used in the following:

- hypersensitivity to the active substances (or to sulphonamide derived medicinal products) or to any of the excipients listed in section 6.1;

- bradycardia;

- cardiogenic shock;

- hypotension;

- metabolic acidosis;

- severe peripheral arterial circulatory disturbances;

- second- or third-degree heart block;

- sick sinus syndrome;

- untreated phaeochromocytoma;

- severe renal failure;

- uncontrolled heart failure.

Blokiuret tablets must not be given during pregnancy or lactation.

Due to its beta-blocker component Blokiuret tablets:

- although contraindicated in uncontrolled heart failure may be used in patients whose signs of heart failure have been controlled. Caution must be exercised in patients whose cardiac reserve is poor.

- may increase the number and duration of angina attacks in patients with Prinzmetal's angina due to unopposed alpha receptor mediated coronary artery vasoconstriction. Atenolol is a beta₁-selective beta-blocker; consequently the use of Blokiuret tablets may be considered although utmost caution must be exercised.

- although contraindicated in severe peripheral arterial circulatory disturbances may also aggravate less severe peripheral arterial circulatory disturbances.

- due to its negative effect on conduction time, caution must be exercised if it is given to patients with first-degree heart block.

- may modify warning signs of hypoglycaemia as tachycardia, palpitation and sweating.

- may mask the cardiovascular signs of thyrotoxicosis.

- will reduce heart rate, as a result of its pharmacological action. In the rare instances when a treated patient develops symptoms which may be attributable to a slow heart rate, the dose may be reduced.

- should not be discontinued abruptly in patients suffering from ischaemic heart disease.

- may cause a more severe reaction to a variety of allergens, when given to patients with a history of anaphylactic reaction to such allergens. Such patients may be unresponsive to the usual doses of adrenaline used to treat the allergic reactions.

- may cause a hypersensitivity reaction including angioedema and urticaria.

- patients with bronchospastic disease should, in general, not receive beta-blockers due to increasing in airways resistance. Atenolol is a beta₁-selective beta-blocker; however this selectivity is not absolute. Therefore the lowest possible dose of Blokiuret tablets should be used and utmost caution must be exercised. If increased airways resistance does occur, Blokiuret tablets should be discontinued and bronchodilator therapy (e.g. salbutamol) administered if necessary.

The label and patient information leaflet for this product state the following warning:

“If you have ever had asthma or wheezing, do not take this medicine without first checking with your doctor”.

- systemic effects of oral beta-blockers may be potentiated when used concomitantly with ophthalmic beta-blockers.

- in patients with phaeochromocytoma must be administered only after alfa-receptor blockade. Blood pressure should be monitored closely.

- caution must be exercised when using anaesthetic agents with Blokiuret tablets. The anaesthetist should be informed and the choice of anaesthetic should be an agent with as little negative inotropic activity as possible. Use of beta-blockers with anaesthetic drugs may result in attenuation of the reflex tachycardia and increase the risk of hypotension. Anaesthetic agents causing myocardial depression are best avoided.

Due to its chlortalidone component:

- plasma electrolyte should be periodically determined in appropriate intervals to detect possible electrolyte imbalance especially hypokalaemia and hyponatraemia.

- hypokalaemia and hyponatraemia may occur. Measurement of electrolytes is recommended, especially in the older patient, those receiving digitalis preparations for cardiac failure, those taking an abnormal (low in potassium) diet or those suffering from gastrointestinal complaints. Hypokalaemia may predispose to arrhythmias in patients receiving digitalis.

- impaired glucose tolerance may occur and diabetic patients should be aware of the potential for increased glucose levels. Close monitoring of glycaemia is recommended in the initial phase of therapy and in prolonged therapy test for glucosuria should be carried out at regular intervals.

- in patients with impaired hepatic function or progressive liver disease, minor alterations in fluid and electrolyte balance may precipitate hepatic coma.

- hyperuricaemia may occur. Only a minor increase in serum uric acid usually occurs but in cases of prolonged elevation, the concurrent use of a uricosuric agent will reverse the hyperuricaemia.

Use is unlikely to result in any impairment of the ability of patients to drive or use machinery. However, it should be taken into account that occasionally dizziness or fatigue may occur.

Tabulated list of adverse reactions

Blokiuret tablets are well tolerated. In clinical studies, the undesired events reported are usually attributable to the pharmacological actions of its components.

The following undesired events, listed by body system, have been reported with the following frequencies: 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); not known (cannot be estimated from the available data).

Discontinuance of Blokiuret tablets should be considered if, according to clinical judgement, the well-being of the patient is adversely affected by any of the above reactions.

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. Website: www.mhra.gov.uk/yellowcard

The symptoms of overdosage may include bradycardia, hypotension, acute cardiac insufficiency and bronchospasm.

General treatment should include: close supervision, treatment in an intensive care ward, the use of gastric lavage, activated charcoal and a laxative to prevent absorption of any drug still present in the gastrointestinal tract, the use of plasma or plasma substitutes to treat hypotension and shock. The possible use of haemodialysis or haemoperfusion may be considered.

Excessive bradycardia may be countered with atropine 1-2 mg intravenously and/or a cardiac pacemaker. If necessary, this may be followed by a bolus dose of glucagon 10 mg intravenously. If required, this may be repeated or followed by an intravenous infusion of glucagon 1-10 mg/hour depending on response. If no response to glucagon occurs or if glucagon is unavailable, a beta-adrenoceptor stimulant such as dobutamine 2.5 to 10 micrograms/kg/minute by intravenous infusion may be given. Dobutamine, because of its positive inotropic effects could be used to treat hypotension and acute cardiac insufficiency. It is likely that these doses would be inadequate to reverse the cardiac effects of beta-blocker blockade if a large overdose has been taken. The dose of dobutamine should therefore be increased if necessary to achieve the required response according to the clinical condition of the patient.

Bronchospasm can usually be reversed by bronchodilators.

Excessive diuresis should be countered by maintaining normal fluid and electrolyte balance.

Pharmacotherapeutic group: Beta-blocking agents, selective, and other diuretics.

C07C B03

Blokiuret tablets combines the antihypertensive activity of two agents, a beta-blocker (atenolol) and a diuretic (chlortalidone).

Atenolol

Atenolol is beta₁-selective (i.e. acts preferentially on beta₁-adrenergic receptors in the heart). Selectivity decreases with increasing dose.

Atenolol is without intrinsic sympathomimetic and membrane-stabilising activities and, as with other beta-adrenoceptor blocking drugs, has negative inotropic effects (and is therefore contraindicated in uncontrolled heart failure).

As with other beta-blockers, the mode of action in the treatment of hypertension is unclear.

It is unlikely that any additional ancillary properties possessed by S (-) atenolol, in comparison with the racemic mixture, will give rise to different therapeutic effects.

Atenolol is effective and well-tolerated in most ethnic populations. Black patients respond better to the combination of atenolol and chlortalidone, than to atenolol alone.

The combination of atenolol with thiazide-like diuretics has been shown to be compatible and generally more effective than either drug used alone.

Chlortalidone

Chlortalidone, a monosulfonamyl diuretic, increases excretion of sodium and chloride. Natriuresis is accompanied by some loss of potassium. The mechanism by which chlortalidone reduces blood pressure is not fully known but may be related to the excretion and redistribution of body sodium.

Atenolol

Absorption of atenolol following oral dosing is consistent but incomplete (approximately 40-50%) with peak plasma concentrations occurring 2-4 hours after dosing. The atenolol blood levels are consistent and subject to little variability. There is no significant hepatic metabolism of atenolol and more than 90% of that absorbed reaches the systemic circulation unaltered. The plasma half-life is about 6 hours but this may rise in severe renal impairment since the kidney is the major route of elimination. Atenolol penetrates tissues poorly due to its low lipid solubility and its concentration in brain tissue is low. Plasma protein binding is low (approximately 3%).

Chlortalidone

Absorption of chlortalidone following oral dosing is consistent but incomplete (approximately 60%) with peak plasma concentrations occurring about 12 hours after dosing. The chlortalidone blood levels are consistent and subject to little variability. The plasma half-life is about 50 hours and the kidney is the major route of elimination. Plasma protein binding is high (approximately 75%).

Coadministration of chlortalidone and atenolol has little effect on the pharmacokinetics of either.

Blokiuret tablets is effective for at least 24 hours after a single oral daily dose. This simplicity of dosing facilitates compliance by its acceptability to patients.

Atenolol and chlortalidone are drugs on which extensive clinical experience has been obtained. Relevant information for the prescriber is provided elsewhere in the Summary of Product Characteristics.

Not applicable.

No special requirements for disposal.