DEALING WITH INTRACTABLE HYPERTENSION

Intractable hypertension is defined as the unsatisfactory control of BP despite the concurrent administration of 3 or more conventional hypotensive agents (!3-blocker + diuretic + either prazosin, hydralazine or methyldopa) in the maximum dose. In most cases unsatisfactory control can be explained by the following reasons: Compliance: poor patient compliance is the commonest cause of poor control. As many as 50% of asymptomatic patients who are started on antihypertensive medication fail to comply within 3 months. Daily or twice daily regimens together with careful follow up may help to minimise the problem. A useful parameter, which can be easily used to check compliance in patients receiving !3-blockers, is resting pulse rate, which should be slow compared with baseline. A.dequate dosage: when a modest dosage fails to control pressure, a maximal dose should be administered to patients free from side effects, before designating the hypertension intractable. If the hypertension is resistant at maximal dosage of one particular drug or where side effects are troublesome, changing to an allied drug (i.e. from propranolol to atenolol) with different pharmacological properties, or to a drug with multiple hypotensive mechanisms (labetalol or indapamide) may be useful. If a thiazide diuretic alone fails to control BP adequately, satisfactory control may be achieved if combined with one or two other agents. False tolerance: loss of BP control secondary to sodium and water retention following the administration of antihypertensive drugs (except diuretics and {j-blockers) is called 'false tolerance.' This can generally be overcome by increasing the dose and/or potency of the diuretic in the drug combination. Thiazides are unlikely to be effective in patients with a creatinine clearance less than 20 mljmin yet loop diuretics such as frusemide (furosemide) retain their potency. Undetected secondary hypertension: the possibility of secondary hypertension should be considered especially if initial satisfactory control is followed by progressive deterioration in a compliant patient. Common etiologies of secondary hypertension include drug-induced (oral contraceptives, steroids, liquorice), renal artery stenosis, coarctation of the aorta, adrenocortical adenoma and phaeochromocytoma. For those few patients who fail to respond to this 4-part assessment, treatment with minoxidil (a potent arteriolar vasodilator) or captopril (an angiotensin-converting enzyme inhibitor) will control BP almost without exception. A once-daily dose of 2.5-40mg minoxidil is satisfactory in 80% of patients although a bid dosage may be needed if a large fall in pressure is required. Minoxidil should be administered at an initial dose of 2.5 or 5mg together with a {j­blockerjdiuretic combination, increasing the dose by 2.5 or Smg at 2- or 3-day intervals until control is achieved. Captopril in combination with a diuretic is very effective. Usual daily maintenance doses range between 25-lSOmg bid or tid but must be reduced to one dose every 2-3 days in patients with creatinine clearances of 8-19 mljmin. A precipitate and potentially dangerous fall in pressure may occur in those patients with hypertension resulting predominately from an excessively elevated angiotensin II level. Side effects of minoxidil include fluid retention and hirsutism whereas captopril is associated with a transient loss of taste, skin rash, membranous glomerulopathy and rarely agranulocytosis. Mackay, A.: Journal of the Royal Society of Medicine 76: 537 (Jul 1983)

0156-2703/83/0903-0003/0$01.00/0 © ADlS Press lNPHARMA 3 Sep 1983 3