💊 Beta Blockers
Drug Class & Overview
Beta blockers are a class of medications that block beta-adrenergic receptors, primarily used in cardiovascular medicine. They reduce heart rate, myocardial contractility, and blood pressure.
Mechanism of Action
Beta blockers competitively inhibit the binding of catecholamines (e.g., adrenaline, noradrenaline) to beta-adrenergic receptors. Cardioselective beta blockers primarily block beta-1 receptors in the heart, reducing heart rate and contractility. Non-selective beta blockers also block beta-2 receptors, which can cause bronchoconstriction and peripheral vasoconstriction.
Key Indications
Beta blockers are widely used for hypertension, particularly in younger patients or those with co-existing conditions like angina or anxiety. They are crucial in the management of stable angina, reducing myocardial oxygen demand. In heart failure with reduced ejection fraction, they improve survival and symptoms. They also treat arrhythmias, migraine prophylaxis, and essential tremor.
Contraindications
Absolute contraindications include uncontrolled asthma or severe COPD due to the risk of bronchospasm (especially with non-selective agents). Other contraindications include decompensated heart failure, severe bradycardia, second or third-degree heart block without a pacemaker, and severe peripheral arterial disease. Caution in diabetes due to masking hypoglycaemia symptoms.
Adverse Effects
Common side effects include bradycardia, fatigue, cold extremities, and sleep disturbances (e.g., nightmares). Bronchospasm can occur, particularly with non-selective agents in susceptible individuals. They can worsen peripheral arterial disease and mask the symptoms of hypoglycaemia in diabetic patients. Sexual dysfunction is also reported.
Monitoring
Before and during treatment, heart rate and blood pressure should be regularly monitored. Patients should be advised to report symptoms of bradycardia or worsening respiratory symptoms. In diabetic patients, blood glucose monitoring should be vigilant due to the potential masking of hypoglycaemia symptoms.
Prescribing Safety (OSCE)
Always check for a history of asthma, COPD, or severe bradycardia/heart block. Counsel patients about potential side effects like fatigue, cold extremities, and the importance of reporting breathing difficulties. Advise diabetic patients about the masked symptoms of hypoglycaemia. Be aware of interactions with other rate-limiting drugs.
MLA High-Yield Notes
High-yield topics include the distinction between cardioselective and non-selective agents, their contraindications (especially respiratory diseases), and their role in heart failure (initiation only when stable). Remember the side effects like bradycardia, fatigue, and masking hypoglycaemia. The 'cold extremities' side effect is also often tested.
Common SBA Themes
SBAs frequently test contraindications, especially asthma/COPD. A common scenario involves a patient with a slow heart rate or new-onset wheeze after starting a beta blocker. Questions may also focus on their role in heart failure (initiation only once stable) or masking hypoglycaemia in diabetics.
References
- BNF (British National Formulary)
- NICE (National Institute for Health and Care Excellence)
- MHRA (Medicines and Healthcare products Regulatory Agency)