𝝰-adrenoceptor antagonists (𝝰 blockers)
Inhibit 𝝰1-adrenoceptors in arterioles, thereby reducing tone of vascular smooth muscle and reducing total peripheral resistance....
𝝰-adrenoceptor antagonists (𝝰 blockers)...
- EXAMPLES: Doxazosin, prazosin, tamsulosin, alfuzosin.
- MECHANISM OF ACTION: Inhibit 𝝰1-adrenoceptors in arterioles, thereby reducing tone of vascular smooth muscle and reducing total peripheral resistance.
- Inhibition of 𝝰1-adrenoceptors in periurethral prostatic stroma results in relaxation of internal urethral sphincter and some relief of obstructive urinary symptoms in males.
- Hypertension (i.e. doxazosin, particularly in resistant cases as part of polytherapy).
- Benign prostatic hyperplasia.
- Caution in patients with a susceptibility to heart failure.
- Postural hypotension.
- Dizziness.
- Weakness and fatigue.
- Reflex tachycardia.
- Headache.
- Dry mouth.
- Ejaculatory failure.
- Variable – e.g. doxazosin (t½ ～22 h) extensively metabolised by liver; alfuzosin (t½ ～3–5 h) partially metabolised.
- May cause severe first-dose hypotension therefore need to start at low dose and warn patient of side-effects.
- Enhanced hypotensive effect with antihypertensives and alcohol.
- Centrally acting 𝝰2-adrenoceptor agonists (e.g. clonidine, 𝝰 methyldopa) also have an antihypertensive effect (mediated via suppression of the vasomotor centre in the brain).
- These agents are rarely used due to infrequent but potentially severe adverse effects (𝝰 methyldopa may cause hepatitis). 𝝰 methyldopa continues to be used for hypertension in pregnancy.
