From the FDA Drug Label
CONTRAINDICATIONS Anuria, hepatic coma or precoma, known allergy or hypersensitivity to metolazone. The contraindications for metolazone are:
- Anuria
- Hepatic coma or precoma
- Known allergy or hypersensitivity to metolazone 1
From the Research
Metolazone is contraindicated in patients with anuria, hepatic coma, hypersensitivity to metolazone or other thiazide diuretics, and severe renal impairment, as evidenced by the most recent study 2 which highlights the increased risk of mortality, hypokalemia, hyponatremia, and worsening renal function associated with its use.
Key Contraindications and Precautions
- Anuria (complete absence of urine production)
- Hepatic coma
- Hypersensitivity to metolazone or other thiazide diuretics
- Severe renal impairment
Special Considerations
- Patients with severe liver disease should be treated with caution, as minor alterations in fluid and electrolyte balance may precipitate hepatic coma 3.
- Metolazone should be avoided in patients with a history of sulfonamide allergy due to potential cross-reactivity.
- Caution is warranted in patients with gout or hyperuricemia, as metolazone can increase uric acid levels and potentially trigger gout attacks 4.
- Patients with diabetes mellitus should be monitored closely, as the medication may affect glucose control.
- Pregnant women, especially in the first trimester, should avoid metolazone unless absolutely necessary due to potential risks to the fetus.
Mechanism and Monitoring
- Metolazone works by inhibiting sodium and chloride reabsorption in the distal tubule of the kidney, which can lead to significant electrolyte imbalances, particularly hypokalemia, hyponatremia, and hypochloremic alkalosis 5.
- Patients with pre-existing electrolyte abnormalities require careful monitoring, as metolazone can exacerbate these conditions.
Clinical Evidence
- A recent study 2 found that metolazone was associated with increased mortality, hypokalemia, hyponatremia, and worsening renal function in patients with acute decompensated heart failure.
- Another study 4 found that low-dose metolazone (<5 mg) was effective and relatively safe in patients with refractory heart failure.
- The combination of metolazone and loop diuretics can be effective in treating fluid retention, but requires careful monitoring to avoid excessive diuresis and electrolyte imbalances 6.