💊 Calcium Channel Blockers (Dihydropyridine)
Drug Class & Overview
Dihydropyridine calcium channel blockers (DHP-CCBs) are a class of cardiovascular medications primarily used for hypertension and angina. They predominantly act on vascular smooth muscle, causing vasodilation.
Mechanism of Action
DHP-CCBs block L-type voltage-gated calcium channels, primarily in vascular smooth muscle cells. This reduces calcium influx, leading to relaxation of arterial smooth muscle and subsequent vasodilation. This peripheral vasodilation reduces systemic vascular resistance and blood pressure, and in angina, it improves coronary blood flow.
Key Indications
DHP-CCBs are a first-line treatment for essential hypertension, particularly in older patients or those of Afro-Caribbean descent. They are also effective in the management of stable angina, reducing myocardial oxygen demand and improving coronary blood flow. They can be used for Raynaud's phenomenon due to their vasodilatory properties.
Contraindications
Absolute contraindications include significant aortic stenosis due to the risk of precipitating hypotension and myocardial ischaemia. They should be used with caution in severe heart failure with reduced ejection fraction, although some (e.g., amlodipine) are considered safer than others. Avoid in unstable angina or acute myocardial infarction.
Adverse Effects
Common side effects are related to vasodilation and include ankle oedema, flushing, headache, and dizziness. Reflex tachycardia can occur, particularly with shorter-acting agents. Gingival hyperplasia is a less common but recognised side effect with chronic use. Constipation can also occur.
Monitoring
Blood pressure should be monitored regularly to assess efficacy and identify hypotension. Patients should be advised to monitor for and report symptoms of ankle oedema or dizziness. Heart rate should also be checked, especially when initiating treatment, to detect reflex tachycardia.
Prescribing Safety (OSCE)
Always check for significant aortic stenosis or severe heart failure. Counsel patients about common side effects like ankle oedema, flushing, and headache, reassuring them that these often improve with time. Advise them to report persistent or troublesome symptoms. Be aware of potential interactions with grapefruit juice.
MLA High-Yield Notes
High-yield topics include their primary action on vascular smooth muscle, the common side effects (ankle oedema, flushing, headache), and their role as a first-line antihypertensive in certain demographics. Understand the difference in action compared to non-DHP CCBs. Remember the risk of reflex tachycardia.
Common SBA Themes
SBAs often focus on the classic side effect of ankle oedema, asking for its management or differentiation from heart failure oedema. Questions may also test their use as a first-line agent in specific patient populations (e.g., elderly, Afro-Caribbean). The distinction between DHP and non-DHP CCBs is a common theme.
References
- BNF (British National Formulary)
- NICE (National Institute for Health and Care Excellence)
- MHRA (Medicines and Healthcare products Regulatory Agency)