Alpha-adrenoceptor Blocking Drugs

Synonym: Alpha-blockers
Alpha-adrenoreceptors are found in nerve endings in the smooth muscle walls of arterioles and in the prostate gland.

Drugs which block post-synaptic alpha-receptors are useful in the management of hypertension and in benign prostatic hypertrophy.

Hypertension

• In arterioles, alpha-blockade causes vasodilatation.
• NICE guidance recommends that alpha-blockers should not be used for first line therapy.^1,2
• Most recent guidance from the British Hypertension Society, is that they should be reserved as a third-line addition for patients resistant to other agents.³
• Guidance from both organisations is based on ALLHAT (Anti-hypertensive and Lipid-Lowering Treatment to prevent Heart Attack Trial), which assessed the hypertensive management of over 42,000 patients. The alpha-blocking arm of the trial was stopped two years early because it showed that patients taking the class representative (doxazosin) were 25% more likely to have major cardiovascular events than chlorthalidone, and because the chance of the drug achieving better hypertensive control than chlorthalidone was remote.⁴

Benign Prostatic Hypertrophy

Alpha-blockade relieves symptoms by reducing prostate and bladder neck smooth muscle control.^5,6

• History of postural hypotension - particularly micturition syncope⁷.
• Lactation:⁷ some alpha-blockers are contra-indicated; see individual monographs.
• Heart failure or impaired left ventricular function - ALLHAT showed increased incidence heart failure compared to chlorthalidone.⁴

(see also individual drug monographs)⁶

• Hepatic impairment - lack of information, manufacturers advise caution.⁴ Limited comparative clinical trials have however been reassuring.⁸
• Pregnancy - no evidence of teratogenicity, but due to lack of data, manufacturers advise use only when potential benefit outweighs risk.⁷
• Driving and using machinery - manufacturers advise caution for 24 hours after initiation of drugs or increase in dosage due to risk of syncope or orthostatic symptoms.⁹

• Antihypertensives and diuretics - enhanced hypotensive effect, and risk of first-dose hypotension.
• General anaesthetics, MAOIs and phosphodiesterase inhibitors can also increase the hypotensive effect.

• Cardiovascular - orthostatic hypotension,¹⁰ dizziness (more common in the elderly). Palptations can also occur.⁷ Some evidence that tamsulosin and alfuzosin more selective and causes less side effects than other alpha-blockers used for BPH.¹¹
• Central nervous system effects⁷ - commonly weakness, lethargy, headaches, oedema, sleep disturbance, nausea, rhinitis.
• Less common effects⁷ - gastro-intestinal symptoms, agitation, tremor, rash, pruritus.
• Rare⁷ - blurred vision, epistaxis, haematuria, thrombocytopenia, purpura, leucopenia, hepatitis, jaundice, cholestasis, urinary incontinence, priapism, impotence.

In the elderly, dizziness and postural hypotension are more common. Tamsulosin and alfuzosin are prostate-selective-alpha1a-antagonists and don't require titration.

• Check medication - is patient taking other medication likely to lower blood pressure?
• Warn re first-dose hypotension and not to drive or operate machinery within 24 hours of starting drug.
• Drugs in this groups vary in terms of the need for titratiion. Tamsulosin and alfuzosin are prostate-selective and do not require tritration. See individual drug monographs for further details.

No specific monitoring requirements, other than as dictated by the condition.