Noncompliance

Nonadherence to drug regimen

Nonadherence to sodium restriction

True diuretic resistance

Altered intestinal absorption of loop diuretics

Decreased renal perfusion caused by low volume, arterial disease, or drug use (e.g., ACE inhibitors, NSAIDs)

Pharmacokinetic causes related to diuretic half-life

Reduced tubular secretion caused by low volume, kidney disease, or drug use

Tolerance caused by chronic use of loop diuretics