Drugs used in hypertension and angina

Two groups of drugs, (3-adrenergic blockers and calcium channel blockers, are used in both hypertension and angina. Several drugs for hypertension are used also in the treatment of heart failure.

Diuretics (see also Ch. 26)

Diuretics, particularly the thiazides, are useful antihypertensives. They cause an initial loss of sodium with a parallel contraction of the blood and extracellular fluid volume. The effect may reach 10% of total body sodium but it is not maintained. After several months of treatment, the main blood pressure lowering effect appears to reflect a reduced responsiveness of resistance vessels to endogenous vasoconstrictors, principally noradrenaline. While this hyposensitivity may be a consequence of the sodium depletion, thiazides are generally more effective antihypertensive agents than loop diuretics, despite causing less salt loss, and evidence suggests an independent action of thiazides on an unidentified ion-channel on vascular smooth muscle cell membranes. Maximum effect on blood pressure is delayed for several weeks and other drugs are best added after this time. Adverse metabolic effects of thiazides on serum potassium, blood lipids, glucose tolerance, and uric acid metabolism led to suggestions that they should be replaced by newer agents not having these effects. It is, however, now recognised that unnecessarily high doses of thiazides have been used in the past and that with low doses, e.g. bendro-fluazide (bendroflumethiazide) 1.25-2.5 mg/d or less (or hydrochlorothiazide 12.5-25 mg), thiazides are both effective and well-tolerated. Moreover, they are not only by far the cheapest antihypertensive agents available worldwide but have proved to be the most effective in several outcome trials in preventing the major complications of hypertension, myocardial infarction and stroke. The characteristic reduction in renal calcium excretion induced by thiazides may, in long-term therapy, also reduce the occurrence of hip fractures in older patients and benefit women with postmenopausal osteoporosis.

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