What are the side effects of metolazone?

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Last updated: March 2, 2026 • View editorial policy

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Metolazone Side Effects

Metolazone causes severe electrolyte disturbances—particularly hypokalemia, hyponatremia, and metabolic alkalosis—in approximately 10% of treatment episodes, along with worsening renal function, and these adverse effects occur more frequently than with high-dose loop diuretics alone. 1, 2, 3

Common Electrolyte and Metabolic Disturbances

  • Hypokalemia is the most frequent electrolyte abnormality, occurring in a substantial proportion of patients receiving metolazone, especially when combined with loop diuretics 1, 2, 3
  • Hyponatremia develops commonly during metolazone therapy; clinically important hyponatremia (<125 mmol/L) occurs in approximately 10% of treatment episodes 1, 2, 3
  • Hypochloremic alkalosis results from excessive chloride loss in the distal tubule 1
  • Hyperglycemia and glycosuria can occur, particularly in patients with diabetes or pre-diabetes 1
  • Hyperuricemia is common and may precipitate acute gouty attacks in susceptible patients 1, 4
  • Hypercalcemia may develop during prolonged therapy 1
  • Hypomagnesemia and hypophosphatemia occur but are less frequently monitored 1

Renal Effects

  • Worsening renal function is strongly associated with metolazone use, manifesting as increases in serum creatinine and blood urea nitrogen (BUN) 1, 2, 4, 3
  • Initial treatment produces small increases in serum creatinine secondary to diuresis-induced volume depletion, which may be acceptable if the patient remains asymptomatic 4
  • Azotemia from excessive volume depletion is a significant risk, particularly when metolazone is combined with loop diuretics 5

Cardiovascular and Hemodynamic Effects

  • Orthostatic hypotension occurs frequently due to excessive volume depletion 1
  • Excessive volume depletion and hemoconcentration can lead to prerenal azotemia and tissue hypoperfusion 1
  • Venous thrombosis has been reported, likely related to hemoconcentration 1
  • Chest pain/discomfort and palpitations may occur 1

Severe Dermatologic and Hypersensitivity Reactions

  • Toxic epidermal necrolysis (TEN) and Stevens-Johnson Syndrome are rare but life-threatening reactions 1
  • Necrotizing angiitis (cutaneous vasculitis) and skin necrosis represent severe hypersensitivity phenomena 1
  • Photosensitivity dermatitis is a common, less severe skin reaction 1
  • Urticaria, pruritus, purpura, and petechiae occur with variable frequency 1

Hematologic Complications

  • Aplastic/hypoplastic anemia is a rare but serious adverse effect 1
  • Agranulocytosis, leukopenia, and thrombocytopenia can occur and require immediate discontinuation 1

Gastrointestinal Effects

  • Hepatitis and intrahepatic cholestatic jaundice are serious hepatic complications 1
  • Pancreatitis is a rare but potentially life-threatening adverse effect 1
  • Nausea, vomiting, epigastric distress, diarrhea, and constipation are common gastrointestinal complaints 1
  • Anorexia and abdominal bloating/pain may occur 1

Neurologic and Psychiatric Effects

  • Syncope can result from severe volume depletion or electrolyte disturbances 1
  • Neuropathy and paresthesias have been reported 1
  • Psychotic depression is a rare but serious psychiatric complication 1
  • Dizziness/lightheadedness, drowsiness, fatigue, and weakness are common complaints 1
  • Vertigo and headache occur with variable frequency 1
  • Restlessness resulting in insomnia may develop 1

Musculoskeletal Effects

  • Acute gouty attacks are precipitated by hyperuricemia 1, 4
  • Muscle cramps or spasm occur frequently, particularly with severe electrolyte depletion 1
  • Joint pain has been reported 1

Other Adverse Effects

  • Transient blurred vision may occur 1
  • Impotence has been reported in male patients 1
  • Dry mouth and chills are less common complaints 1

Comparative Risk: Metolazone vs. High-Dose Loop Diuretics

  • Metolazone is independently associated with increased mortality after controlling for baseline characteristics and propensity to receive the drug (hazard ratio 1.20,95% CI 1.04-1.39) 3
  • High-dose loop diuretics are NOT associated with increased mortality under the same experimental conditions (hazard ratio 0.97 per 100 mg IV furosemide, 95% CI 0.90-1.06) 3
  • Metolazone shows stronger associations with hyponatremia, hypokalemia, and worsening renal function compared to high-dose loop diuretics, even after propensity adjustment 3

Critical Monitoring Requirements

  • Check serum potassium, sodium, and creatinine 1-2 days after initiating metolazone, then every 3-7 days during active treatment 5
  • Monitor daily weights targeting 0.5-1.0 kg loss per day 5
  • Assess for signs of excessive diuresis: hypotension, dizziness, oliguria, and marked fatigue 5
  • Watch for severe hyponatremia (sodium <125 mmol/L) or severe hypokalemia (potassium <3.0 mmol/L), which require immediate drug cessation 5

When to Reduce or Discontinue Metolazone

  • Moderate or severe adverse reactions warrant dose reduction or therapy withdrawal 1
  • Severe hyponatremia (<120-125 mmol/L) requires immediate discontinuation 5
  • Severe hypokalemia (<3.0 mmol/L) mandates stopping the drug 5
  • Progressive renal failure despite adequate diuresis necessitates reassessment 5
  • Anuria is an absolute contraindication to continued use 5

References

5
Guideline

Timing of Metholazone Administration in Relation to Loop Diuretics

Praxis Medical Insights: Practical Summaries of Clinical Guidelines, 2026

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This information is intended for healthcare professionals. Any medical decision-making should rely on clinical judgment and independently verified information. The content provided herein does not replace professional discretion and should be considered supplementary to established clinical guidelines. Healthcare providers should verify all information against primary literature and current practice standards before application in patient care. Dr.Oracle assumes no liability for clinical decisions based on this content.