Can losartan (angiotensin II receptor antagonist) cause myositis?

Losartan and Myositis: Risk Assessment

Losartan can cause myositis in rare cases, as documented in the FDA drug label which lists rhabdomyolysis among its postmarketing adverse effects. 1

Evidence for Losartan-Associated Muscle Effects

• Rhabdomyolysis is specifically listed as a postmarketing adverse reaction in the FDA drug label for losartan, indicating a potential for serious muscle injury 1
• Musculoskeletal adverse effects including myalgia and arthralgia are documented in clinical trials of losartan 1
• The FDA label categorizes these muscle-related effects under "Musculoskeletal and Connective Tissue Disorders" 1

Mechanism and Risk Factors

• The exact mechanism by which losartan might cause myositis is not fully elucidated in the available evidence
• Research suggests that angiotensin II receptor blockers (ARBs) like losartan may affect muscle tissue through various pathways:
  • In some experimental models, losartan has been shown to reduce fibrosis but potentially hinder functional recovery in volumetric muscle loss injury 2
  • Paradoxically, losartan has exacerbated muscle damage in certain muscular dystrophy models 3

Clinical Presentation and Diagnosis

• Patients with drug-induced myositis typically present with:
  • Proximal muscle weakness, particularly in the extremities 4
  • Difficulty standing up, lifting arms, and moving around 4
  • Myalgia (muscle pain) in severe cases 4
• Diagnostic workup should include:
  • Measurement of muscle enzymes, especially creatine kinase (CK), which is often markedly elevated 4
  • Assessment of inflammatory markers 4
  • Electromyography (EMG) which may show muscle fibrillations indicative of myopathy 4
  • MRI which can show increased intensity and edema in affected muscles 4
  • Muscle biopsy in cases where diagnosis remains uncertain 4

Differential Diagnosis

• When evaluating muscle symptoms in patients on losartan, consider other causes:
  • Statin-induced myopathy (particularly important as many patients on losartan may also be on statins) 4
  • Polymyalgia rheumatica 4
  • Fibromyalgia 4
  • Inflammatory myositis from other causes 4
  • Muscle dystrophies 4

Management Recommendations

• If myositis is suspected in a patient taking losartan:
  • Consider discontinuation of losartan and switching to an alternative antihypertensive agent 1
  • Monitor muscle enzyme levels (CK) and inflammatory markers 4
  • In severe cases with significant muscle involvement, high-dose corticosteroids may be required 4
  • For cases with poor response to corticosteroids or life-threatening presentations, plasmapheresis may be considered 4

Clinical Pearls and Pitfalls

• Myositis can have a fulminant necrotizing course with rhabdomyolysis and may involve vital skeletal muscle, requiring urgent treatment 4
• The risk of myositis with losartan appears to be rare but real, as evidenced by its inclusion in the FDA drug label 1
• Consider alternative antihypertensive medications in patients who develop unexplained muscle symptoms while on losartan 1
• There have been case reports of other neurological effects with losartan, including tremors and dysarthria, suggesting potential neuromuscular effects 5

While myositis is not among the most common side effects of losartan, clinicians should remain vigilant about this potential adverse effect, particularly in patients presenting with unexplained muscle weakness, pain, or elevated muscle enzymes.