What is the diuretic that sounds like metazalone?

Metolazone: The Diuretic That Sounds Like Metazalone

The diuretic that sounds like "metazalone" is metolazone, a thiazide-like diuretic commonly used in heart failure management, particularly in combination with loop diuretics for resistant edema.

Pharmacology and Classification

Metolazone is a quinazoline diuretic with properties similar to thiazide diuretics. It works primarily by:

• Inhibiting sodium reabsorption at the cortical diluting site in the renal tubules 1
• Causing sodium and chloride excretion in approximately equivalent amounts
• Increasing potassium excretion due to increased sodium delivery to distal tubular exchange sites
• Having some proximal tubule action, shown by increased excretion of phosphate and magnesium 1

Unlike standard thiazides, metolazone maintains effectiveness even in patients with significantly reduced glomerular filtration rates (below 20 mL/min), making it particularly valuable in patients with renal impairment 1.

Clinical Use in Heart Failure

Metolazone is primarily used in the following scenarios:

• As add-on therapy to loop diuretics in patients with resistant edema 2
• When diuretic resistance develops with loop diuretics alone 2
• For patients with severe heart failure requiring enhanced diuresis 2

The 2022 AHA/ACC/HFSA Heart Failure Guidelines specifically state that "for patients with HF and congestive symptoms, addition of a thiazide (e.g., metolazone) to treatment with a loop diuretic should be reserved for patients who do not respond to moderate- or high-dose loop diuretics to minimize electrolyte abnormalities" 2.

Dosing

Standard dosing for metolazone in heart failure:

• Initial daily dose: 2.5 mg once daily 2
• Maximum total daily dose: 20 mg 2
• Duration of action: 12-24 hours 2

For resistant edema, a common approach is to add 2.5 mg of metolazone for 2-3 days to the loop diuretic regimen, then return to the usual maintenance dose of loop diuretic when weight stabilizes 2.

Important Precautions

When using metolazone, particularly in combination with loop diuretics, be aware of:

1. Risk of severe electrolyte disturbances: The combination can cause severe hyponatremia, hypochloremia, alkalosis, and hypokalemia 3

2. Potent synergistic effect: When combined with furosemide, metolazone produces marked diuresis even in patients with refractory edema 1

3. Need for careful monitoring: Due to potential for excessive diuresis, patients should have:

   • Daily weight monitoring
   • Regular electrolyte checks, especially within 5-7 days of initiation
   • Renal function monitoring 4

4. Risk of volume depletion: If excessive diuresis occurs with the combination, both drugs should be temporarily discontinued rather than just reducing doses 5

Clinical Pearls

• Metolazone has slower and sometimes erratic absorption compared to other diuretics 5
• It maintains effectiveness even in advanced renal dysfunction, unlike standard thiazides 6
• When combined with spironolactone, the potassium-wasting effect of metolazone can be counterbalanced 7
• Diuretic effect typically begins within one hour of administration and may persist for 24 hours or more 1

Metolazone represents an important tool in managing resistant fluid overload, particularly in heart failure patients who have become refractory to standard loop diuretic therapy alone. However, its potent effect requires careful monitoring to prevent excessive diuresis and electrolyte abnormalities.