Amlodipine Thiazide diuretics

Following the guidelines of the British Hypertension Society, Mr WD should be prescribed a thiazide diuretic and a calcium channel blocker, so a good combination might be nifedipine LA 20 mg or 30 mg once daily or amlodipine 5 mg once daily, plus bendroflumethiazide 2.5 mg once daily. However, we know that his renal function is poor, with a calculated GFR of approximately 25 mL/min, so he is borderline for thiazides to be clinically effective. In this instance, it might be prudent to prescribe an ACE inhibitor instead, for example, enalapril 5-fO mg twice daily. 

Nifedipine can increase urinary potassium loss in patients treated with thiazide diuretics (17), but it has no effect on adrenaline-induced hypokalemia (18). In the Treatment of Mild Hypertension Study, 4 years of monotherapy with amlodipine maleate caused no change compared with placebo in the serum potassium, uric acid, aspartate transaminase, or creatinine of 114 hypertensive patients (19). 

The results of the Antihypertensive and Lipid-Lowering Treatment to Prevent Heart Attack Trial (ALLHAT) was the deciding evidence that the JNC7 used to justify thiazide diuretics as first-line therapy." It was designed to test the hypothesis that newer antihypertensive agents (an a-blocker, ACE inhibitor, and dihydropyridine CCB) would be superior to thiazide diuretic therapy. The primary objective was to compare the combined end point of fatal coronary heart disease and nonfatal myocardial infarction. Other hypertension-related complications (e.g., heart failure and stroke) were evaluated as secondary end points. This was the largest hypertension trial ever conducted and included 42,418 patients aged 55 years and older with hypertension and one additional cardiovascular risk factor. This prospective, double-blind trial randomized patients to chlorthalidone (a thiazide diuretic), amlodipine (dihydropyridine CCB), doxazosin (a-blocker), or lisinopril (ACE inhibitor) for a mean follow-up of 4.9 years. 

The manufacturers say that amlodipine has been safely given with thiazide diuretics and no dosage adjustment of amlodipine is required. Additive antihypertensive effects are expected when diuretics such as hydrochlorothiazide are used in combination with calcium-channel blockers, and such combinations are used clinically. 

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