The risk of worsening of myasthenia by cardiovascular medication as reflected by reporting frequency.

Background And Purpose: Some groups of cardiovascular drugs (beta-blocking drugs, Ca antagonists, antiarrhythmics) are listed as potentially worsening myasthenia. An empirical basis for alternative recommendations for antihypertensive and antiarrhythmic therapy in myasthenia patients has not yet been provided.

Methods: From the World Health Organization pharmacovigilance database, we retrieved total and myasthenia-related counts of adverse drug reactions for various groups of drugs used in cardiovascular disease and drugs with related mechanism of action used in other indications. We calculated the reporting odds ratio as a measure of a disproportional fraction of myasthenia-related events among all events. A 95% confidence interval of reporting odds ratio (ROR) >1 was taken as an indication for a higher risk. Because our approach involves a considerable number of tests, this situation is referred to as a signal that requires additional confirmation.

Results: A signal for an increased risk was noted for tizanidine, for alpha-blocking drugs, for beta-blocking drugs, and for Ca antagonists. ROR indicated a lower-than-average risk for salbutamol, angiotensin receptor antagonists, oral anticoagulants, thrombocytic function inhibitors, and heparins.

Conclusions: Angiotensin receptor antagonists, angiotensin-converting enzyme inhibitors, and diuretics seem to be safe in antihypertensive therapy. Surprisingly, and yet requiring confirmation by case reports, alpha receptor-blocking drugs seem to carry a risk of myasthenia worsening. Amiodarone seems to be a safe alternative in antiarrhythmic therapy in patients with myasthenia.