What are the side effects of Lasix (furosemide)?

Side Effects of Furosemide (Lasix)

Furosemide can cause significant fluid and electrolyte disturbances, which are the most common adverse reactions, along with potential for ototoxicity, nephrolithiasis, and other systemic effects. 1

Common Side Effects

• Fluid and Electrolyte Disturbances:

  • Hypokalemia (low potassium) - especially with brisk diuresis, inadequate oral electrolyte intake, cirrhosis, or concomitant use of corticosteroids 1
  • Hyponatremia (low sodium) 1
  • Hypochloremic alkalosis 1
  • Hypomagnesemia 1
  • Hypocalcemia - rarely cases of tetany have been reported 1
  • Dehydration and blood volume reduction - may lead to circulatory collapse, particularly in elderly patients 1

• Clinical Signs of Electrolyte Imbalance:

  • Dryness of mouth, thirst, weakness, lethargy 1
  • Drowsiness, restlessness 1
  • Muscle pains, cramps, or fatigue 1
  • Hypotension, oliguria 1
  • Tachycardia, arrhythmias 1
  • Gastrointestinal disturbances (nausea, vomiting) 1

Renal Effects

• Nephrolithiasis/Nephrocalcinosis:

  • Particularly concerning in premature infants 1
  • Risk increases with long-term use 2
  • Requires monitoring of renal function and renal ultrasonography 1

• Acute Urinary Retention:

  • Can occur in patients with bladder emptying disorders, prostatic hyperplasia, or urethral narrowing 1
  • Due to increased production and retention of urine 1

Ototoxicity

• Hearing Impairment:
  • Tinnitus and hearing loss may occur, especially with high doses 1
  • Risk increases with impaired renal function 1
  • Potentiated in patients with hypoproteinemia (e.g., nephrotic syndrome) 1

Metabolic Effects

• Glucose Metabolism:

  • Increases in blood glucose 1
  • Alterations in glucose tolerance tests 1
  • Rarely, precipitation of diabetes mellitus 1

• Uric Acid Metabolism:

  • Asymptomatic hyperuricemia 1
  • May rarely precipitate gout 1

Cardiovascular Effects

• Hemodynamic Changes:
  • Orthostatic hypotension - may be aggravated by alcohol, barbiturates, or narcotics 1
  • Initial worsening of hemodynamics with IV administration 3
  • Transient decrease in stroke volume and increased systemic vascular resistance 3

Dermatologic and Hypersensitivity Reactions

• Skin Reactions:

  • Photosensitivity - increased skin sensitivity to sunlight 1
  • Rash, pruritus, urticaria 1
  • Severe reactions (rare): toxic epidermal necrolysis, Stevens-Johnson Syndrome 1

• Hypersensitivity:

  • Patients allergic to sulfonamides may also be allergic to furosemide 1
  • Severe anaphylactic or anaphylactoid reactions (rare) 1

Gastrointestinal Effects

• Digestive System:

  • Oral and gastric irritation 1
  • Cramping, diarrhea, constipation 1
  • Nausea, vomiting 1
  • Pancreatitis (rare) 1

• Hepatic Effects:

  • Increased liver enzymes 1
  • Jaundice (intrahepatic cholestatic jaundice) 1
  • Hepatic encephalopathy in patients with hepatocellular insufficiency 1

Hematologic Effects

• Blood Disorders (rare):
  • Aplastic anemia, thrombocytopenia 1
  • Agranulocytosis, hemolytic anemia 1
  • Leukopenia, anemia 1

Special Considerations

• Monitoring Requirements:

  • Regular monitoring of serum electrolytes (particularly potassium), CO2, creatinine, and BUN 1
  • More frequent monitoring during the first few months of therapy 1
  • Urine and blood glucose monitoring in diabetic patients 1

• Drug Interactions:

  • May increase ototoxic potential of aminoglycoside antibiotics 1
  • Digitalis therapy may exaggerate effects of hypokalemia 1

Precautions

• Risk Factors for Adverse Effects:

  • Elderly patients - higher risk for dehydration and electrolyte imbalances 1
  • Patients with hypoproteinemia - increased risk of ototoxicity 1
  • Patients with hepatic insufficiency - risk of hepatic encephalopathy 1
  • Patients with renal insufficiency - increased risk of adverse effects 1

• Contraindications:

  • Anuria 1
  • Severe electrolyte depletion until corrected 1
  • Known hypersensitivity to furosemide 1

The frequency of adverse reactions increases progressively with higher daily doses of furosemide but does not necessarily correlate with total furosemide dose 4. Potassium supplements or potassium-sparing diuretics may help reduce the frequency and severity of hypokalemia 4.