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Should a thiazide diuretic or loop diuretic be used to treat hypertension?
In patients with normal kidney function, thiazide diuretics are preferred to loop diuretics.
The thiazide diuretics have a longer duration of action than do loop diuretics.
Furosemide, for example, has a duration of action of approximately 6 hours. After 6 hours, activation of the renin-angiotensin-aldosterone-system leads to renal sodium retention and limits the antihypertensive effect of the drug. The thiazide diuretics, especially chlorthalidone, have a much longer duration of action.
However, the thiazide diuretics become much less effective when the glomerular filtration rate falls below about 30 mL/min. In patients with impaired kidney function, then, loop diuretics are more effective antihypertensive agents. It must be emphasized that a thiazide or loop diuretic is an essential component of an antihypertensive regimen for patients with resistant hypertension.
Intravenous Loop Diuretic Dose Equivalencies
| DIURETIC | INITIAL DOSE | MAXIMUM DOSE a | CONTINUOUS INFUSION a |
|---|---|---|---|
| Furosemide | 20–40 mg | 200 mg | 40–80 mg bolus, then 5–40 mg/h b |
| Bumetanide | 0.5–1 mg | 8–10 mg | 1 mg bolus, then 0.5–2 mg/h b |
| Torsemide | 10–20 mg | 100 mg | 20 mg bolus, then 5–20 mg/h b |
a High doses of intravenous loop diuretic may be necessary in patients with resistance to diuretics (e.g., those with heart failure, nephrotic syndrome, or kidney failure). See text.
b Repeat loading dose before increasing the infusion rate.
Thiazide Diuretic Doses in Refractory Edema a
| DIURETIC | DOSE |
|---|---|
| Chlorothiazide | 500–1000 mg IV daily or twice daily |
| Hydrochlorothiazide | 25–50 mg by mouth twice daily b |
| Chlorthalidone | 12.5–25 mg by mouth twice daily b |
| Metolazone | 2.5–20 mg by mouth daily b |
a When used in addition to loop diuretic.
b If the loop diuretic is given intravenously, administration of oral thiazide diuretic should precede administration of intravenous loop diuretic by a few hours.
