What are the potential side effects of losartan (angiotensin II receptor antagonist)?

Potential Side Effects of Losartan

The most common side effects of losartan include dizziness, upper respiratory infections, hypotension, and hyperkalemia, with dizziness being the only adverse effect reported more frequently than placebo in clinical trials. 1, 2

Common Side Effects

• Cardiovascular effects:

  • Symptomatic hypotension, particularly in volume- or salt-depleted patients 1
  • Dizziness (most commonly reported drug-specific side effect) 2
  • Orthostatic hypotension 3

• Respiratory effects:

  • Upper respiratory infections ("colds") 1
  • Cough (significantly less common than with ACE inhibitors) 3, 2

• General effects:

  • Fatigue/asthenia 1, 2
  • Headache 2
  • Back pain 1

Serious Side Effects

Renal Effects

• Renal function deterioration:
  • Acute kidney injury may occur, especially in patients with:
    • Renal artery stenosis
    • Chronic kidney disease
    • Severe heart failure
    • Volume depletion 1
  • Regular monitoring of renal function is essential, particularly when initiating therapy 3, 1

Electrolyte Abnormalities

• Hyperkalemia:
  • More common in patients with:
    • Chronic kidney disease
    • Concomitant use of potassium supplements
    • Use of other medications that increase potassium (e.g., spironolactone) 3, 1
  • Requires periodic monitoring of serum potassium 1

Pregnancy-Related Risks

• Fetal toxicity:
  • Pregnancy Category D
  • Use during second and third trimesters can cause:
    • Reduced fetal renal function
    • Oligohydramnios
    • Fetal lung hypoplasia
    • Skeletal deformations
    • Neonatal hypotension, renal failure, and death 1
  • Must be discontinued when pregnancy is detected 1

Special Population Considerations

Elderly Patients

• Generally well-tolerated in elderly populations 4
• No specific dosage adjustment required based on age alone 1
• Monitor for hypotension more carefully, especially when combined with diuretics 3

Patients with Renal Impairment

• No initial dosage adjustment necessary for mild to moderate renal impairment 4
• Close monitoring of renal function is essential 1
• May cause further deterioration in patients with bilateral renal artery stenosis 5

Patients with Hepatic Impairment

• Lower initial doses recommended for patients with hepatic impairment 1
• Reduced metabolism may lead to increased drug exposure 4

Drug Interactions

• Medications that may increase risk of hyperkalemia:

  • Potassium supplements
  • Potassium-sparing diuretics (spironolactone, eplerenone)
  • Other medications containing potassium 1

• Other significant interactions:

  • NSAIDs (including COX-2 inhibitors): May reduce antihypertensive effect and increase risk of renal impairment 1
  • Diuretics: May increase risk of hypotension, especially with first dose 1
  • Lithium: May increase lithium levels 1

Monitoring Recommendations

1. Renal function:

   • Check baseline renal function before starting therapy
   • Monitor within 1-2 weeks after initiation
   • Regular monitoring during dose adjustments 3, 1

2. Serum potassium:

   • Check baseline potassium levels
   • Monitor periodically, especially in patients with risk factors for hyperkalemia 1

3. Blood pressure:

   • Monitor for hypotension, especially after first dose and in volume-depleted patients 1

Advantages Over ACE Inhibitors

• Significantly lower incidence of cough 3, 2
• Similar efficacy profile to ACE inhibitors in hypertension management 6
• May be better tolerated overall, with fewer side effects 3

Important Precautions

• Correct volume or salt depletion before initiating losartan to reduce risk of symptomatic hypotension 1
• Consider withholding or discontinuing therapy in patients who develop significant decrease in renal function 1
• Avoid use during pregnancy; discontinue immediately if pregnancy is detected 1
• Use caution when combining with other medications that affect the renin-angiotensin system 1

Remember that while losartan is generally well-tolerated, individual responses may vary, and close monitoring is essential, particularly when initiating therapy or adjusting doses.