Table 1. Classification of drugs used in the management of hypertension

Mechanism of action	Examples	Relevance to anaesthesia
Diuretics	Hydrochlorothiazide Frusemide	May produce hypokalaemia resulting in dysrhythmias
Vasodilators	Hydralazine Diazoxide	Tachycardia (unpredictable when given IV)
Central sympathetic depression	Clonidine Methyldopa reserpine	Rebound hypertension if withdrawn. Slow acting.
Adrenergic neurone blockers	Guanethidine	Sensitive to vasopressors. Postural hypotension.
Beta blockers	Propranolol Atenolol Labetalol (alpha also)	Avoid in asthmatics and patients with heart failure. Cause bradycardias which usually respond to atropine.
Alpha blockers	Phenoxybenzamine Phentolamine	Tachycardia.
Calcium channel blockers	Nifedipine Verapamil	Vasodilator. Cardiac depressant - avoid combining with beta blockers as extreme hypotension can occur.
Renin - angiotensin inhibitors	Captopril	Potentiate hypotensive action of anaesthetic drugs.