Does losartan (angiotensin II receptor blocker) adversely affect myasthenia gravis?

Losartan Does Not Adversely Affect Myasthenia Gravis

Angiotensin receptor blockers (ARBs) like losartan are safe for patients with myasthenia gravis and represent a preferred option for treating hypertension in these patients. According to recent evidence, ARBs have a lower-than-average risk of exacerbating myasthenia gravis symptoms compared to other cardiovascular medications 1.

Safety Profile of ARBs in Myasthenia Gravis

ARBs have several advantages for patients with myasthenia gravis:

• A 2021 analysis of the World Health Organization pharmacovigilance database showed that ARBs had a lower-than-average risk of myasthenia worsening compared to other cardiovascular medications 1
• Unlike beta-blockers and calcium channel blockers which are known to potentially worsen myasthenia symptoms, ARBs do not directly affect neuromuscular transmission
• The American College of Neurology specifically advises avoiding medications that can worsen myasthenia, including β-blockers, but does not list ARBs among these contraindicated medications 2

Alternative Cardiovascular Medications to Consider

When treating patients with myasthenia gravis who need antihypertensive therapy, the following hierarchy of safety should be considered:

1. First choice: ARBs (like losartan) or ACE inhibitors
2. Second choice: Diuretics
3. Avoid if possible: Beta-blockers, calcium channel blockers, and alpha-blockers

This recommendation is supported by pharmacovigilance data showing that beta-blockers, calcium channel blockers, and alpha-blockers all showed signals for increased risk of myasthenia exacerbation 1.

Mechanism of Safety

The relative safety of ARBs in myasthenia gravis likely stems from their mechanism of action:

• ARBs work by blocking angiotensin II receptors, primarily affecting the renin-angiotensin-aldosterone system
• Unlike calcium channel blockers, which can interfere with neuromuscular junction function at both presynaptic and postsynaptic levels 3, ARBs do not directly impact neuromuscular transmission
• This mechanistic difference explains why calcium antagonists have been reported to cause exacerbation of myasthenia gravis 3, while ARBs have not shown this effect

Monitoring Recommendations

While losartan is considered safe for patients with myasthenia gravis, prudent clinical practice suggests:

• Monitor for any changes in myasthenic symptoms after initiating losartan
• Perform regular neurological assessments to detect any subtle changes in muscle strength
• Consider measuring negative inspiratory force (NIF) and vital capacity (VC) at baseline and follow-up visits to objectively track respiratory function 2
• Be vigilant for rare side effects of losartan such as angioedema, which has been reported in post-marketing surveillance 4

Clinical Implications

For patients with myasthenia gravis requiring antihypertensive therapy:

• ARBs like losartan represent a preferred option due to their favorable safety profile
• Avoid beta-blockers, calcium channel blockers, and alpha-blockers when possible
• If multiple antihypertensive agents are needed, combining an ARB with a diuretic would be preferable to adding agents from higher-risk classes

In conclusion, losartan and other ARBs appear to be safe options for treating hypertension in patients with myasthenia gravis, with evidence suggesting they have a lower risk of exacerbating myasthenic symptoms compared to several other classes of cardiovascular medications.