Aggravation of myasthenia gravis by erythromycin. Erythromycin is not currently recognized as causing clinical aggravation of myasthenia gravis. We report the case of a patient who experienced exacerbations of myasthenia gravis subsequent to each of several doses of intravenous erythromycin. We suggest that erythromycin can cause clinical worsening in patients with disease of the neuromuscular junction. 