Beta blockers Flashcards
Mechanism of action
Beta1-adrenoreceptors are located mainly in the heart, whereas β2-adrenoreceptors are found mostly in smooth muscle of blood vessels and the airways. Via the β1-receptor, β-blockers reduce force of contraction and speed of conduction in the heart. This relieves myocardial ischaemia by reducing cardiac work and oxygen demand, and increasing myocardial perfusion. They improve prognosis in heart failure by ‘protecting’ the heart from the effects of chronic sympathetic stimulation. They slow the ventricular rate in atrial fibrillation mainly by prolonging the refractory period of the atrioventricular (AV) node.
Adverse effects
Fatigue, cold extremities, headache
Warnings
In patients with asthma, β-blockers can cause life-threatening bronchospasm and should be avoided
Interactions
Beta-blockers must not be used with non-dihydropyridine calcium channel blockers (e.g. verapamil, diltiazem). This combination can cause heart failure, bradycardia, and even asystole.
Prescription
Beta-blockers are usually prescribed orally as part of the patient’s regular medication. Dosage varies according to the drug and the indication – the starting dose in heart failure is lower than that for ischaemic heart disease or hypertension.
Administration
Orally administered β-blockers should be taken at equal intervals
Communication
Explain the rationale for treatment as appropriate for the situation. Discuss common side effects, including impotence where relevant. Warn patients with heart failure about the risk of initial deterioration in their symptoms, and advise them to seek medical attention if this occurs. Warn patients with obstructive airways disease to stop treatment and seek medical advice if they develop any breathing difficulty.
Monitoring
The best guide to dosage adjustment is the patient’s symptoms (e.g. chest pain) and heart rate (in ischaemic heart disease, aim for a resting heart rate of around 55–60 beats/min).
