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
|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.