Beta blockers
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Beta-adrenoceptor blocking drugs (beta-blockers) block beta-adrenergic receptors (also known as beta-adrenoceptors or β receptors) which are found mainly in the heart, peripheral vasculature, bronchi, pancreas, and liver.
Properties
Beta-blockers vary in a number of ways:
*Beta-blockers can precipitate bronchospasm and should therefore usually be avoided in patients with a history of asthma. When there is no suitable alternative, it may be necessary for a patient with well-controlled asthma, or chronic obstructive pulmonary disease (without significant reversible airways obstruction), to receive treatment with a beta-blocker for a co-existing condition (e.g. heart failure or following myocardial infarction). In this situation, a cardioselective beta-blocker should be selected and initiated at a low dose by a specialist with close monitoring for adverse effects.
**Beta-blockers slow the heart and can depress the myocardium; they are contra-indicated in patients with second- or third-degree heart block. Beta-blockers should also be avoided in patients with worsening unstable heart failure (care is required when initiating a beta-blocker in those with stable heart failure).
Beta-adrenoceptor background
β receptors are subdivided into β1, β2 and β3 types. The table below summarises effects of agonsim and antagonism (blockade):| Receptor type | Agonism | Blockade |
|---|---|---|
| β1 | Increased contractility (iontropy) Positive chronotropic effect Increased cardiac conduction velocity (dromotropy) Increased amylase secretion | Decreased contractility (inotropy) Decreased heart rate (chronotropy) Decreased cardiac conduction velocity (dromotropy) Decreased cardiac output |
| β2 | Smooth muscle relaxation (bronchodilation for example) | Smooth muscle constriction (bronchospam and peripheral vasoconstriction) |
| β3 | Enhance lipolysis Relaxation of detrusor muscle in the bladder | Bladder detrusor contraction |
Properties
Beta-blockers vary in a number of ways:
- Intrinsic sympathomimetic activity (ISA, partial agonist activity) represents the capacity of beta-blockers to stimulate as well as to block adrenergic receptors. Oxprenolol hydrochloride has intrinsic sympathomimetic activity and tends to cause less bradycardia than other beta-blockers and less coldness of the extremities.
- Lipid vs water soluble. Some beta-blockers are lipid soluble and some are water soluble. Water-soluble beta-blockers, such as atenolol and sotalol hydrochloride, are less likely to enter the brain, and may therefore cause less sleep disturbance and nightmares. Water-soluble beta-blockers are excreted by the kidneys and dose reduction is often necessary in renal impairment.
- Duration of action. Beta-blockers with a relatively short duration of action have to be given two or three times daily. Many of these are, however, available in modified-release formulations so that administration once daily is adequate for hypertension. For angina twice-daily treatment may sometimes be needed even with a modified-release formulation. Some beta-blockers, such as atenolol and bisoprolol have an intrinsically longer duration of action and need to be given only once daily.
- Cardioselectivity. Some beta blockers are considered cardioselective as they predominantly bind β1 adrenoceptors in the myocardium with little activity at β2 receptors in the bronchial smooth muscle and peripheries. Atenolol, bisoprolol and metoprolol are examples of cardioselective beta blockers. Note that whilst they predominantly bind β1 they are not cardiospecific so β2 side effects may still occur but to a lesser extent.
Contraindications
- Asthma*
- Cardiogenic shock
- Hypotension
- Marked bradycardia
- Metabolic acidosis
- Phaeochromocytoma (apart from specific use with alpha-blockers)
- Prinzmetal’s angina
- 2nd or 3rd degree AV block**
- Severe peripheral arterial disease
- Sick sinus syndrome
- Uncontrolled heart failure**
*Beta-blockers can precipitate bronchospasm and should therefore usually be avoided in patients with a history of asthma. When there is no suitable alternative, it may be necessary for a patient with well-controlled asthma, or chronic obstructive pulmonary disease (without significant reversible airways obstruction), to receive treatment with a beta-blocker for a co-existing condition (e.g. heart failure or following myocardial infarction). In this situation, a cardioselective beta-blocker should be selected and initiated at a low dose by a specialist with close monitoring for adverse effects.
**Beta-blockers slow the heart and can depress the myocardium; they are contra-indicated in patients with second- or third-degree heart block. Beta-blockers should also be avoided in patients with worsening unstable heart failure (care is required when initiating a beta-blocker in those with stable heart failure).
Beta-blockers & pregnancy
Beta-blockers may cause intra-uterine growth restriction, neonatal hypoglycaemia, and bradycardia with greater risk in severe hypertension. Available information does not suggest the use of labetalol in pregnancy increases the chance of birth defects and labetalol is considered first line treatment for hypertension in pregnancy by NICE.Side effects
- Fatigue
- Coldness of the extremities (less common with those with ISA)
- Sleep disturbances with nightmares (less common with water-soluble beta-blockers).
- Hypoglycaemia or hyperglycaemia (in patients with or without diabetes)
- Abdominal discomfort
- Bradycardia
- Confusion
- Depression
- Diarrhoea
- Dizziness
- Dry eye (reversible on discontinuation)
- Dyspnoea
- Erectile dysfunction
- Headache
- Heart failure
- Nausea and vomiting
- Paraesthesia
- Peripheral vascular disease
- Rash (reversible on discontinuation)
- Syncope
- Visual impairment
Beta-blockers should be avoided altogether in those with frequent episodes of hypoglycaemia
Beta-blockers, especially when combined with a thiazide diuretic, should be avoided for the routine treatment of uncomplicated hypertension in patients with diabetes or in those at high risk of developing diabetes.
Beta-blockers, especially when combined with a thiazide diuretic, should be avoided for the routine treatment of uncomplicated hypertension in patients with diabetes or in those at high risk of developing diabetes.