Allopurinol should never be used in combination with azathioprine because the two drugs share a common degradation pathway; the result may be severe bone marrow suppression due to increased effects of the azathioprine. Drugs with Interactions in Myasthenia Gravis (MG) Drugs That May Exacerbate MG Antibiotics Aminoglycosides: e.g., streptomycin, tobramycin, kanamycin Quinolones: e.g., ciprofloxacin, levofloxacin, ofloxacin, gatifloxacin Macrolides: e.g., erythromycin, azithromycin Nondepolarizing muscle relaxants for surgery d-Tubocurarine (curare), pancuronium, vecuronium, atracurium Beta-blocking agents Propranolol, atenolol, metoprolol Local anesthetics and related agents Procaine, Xylocaine in large amounts Procainamide (for arrhythmias) Botulinum toxin Botox exacerbates weakness Quinine derivatives Quinine, quinidine, chloroquine, mefloquine (Lariam) Magnesium Decreases acetylcholine release Penicillamine May cause MG Check point inhibitors May cause MG and other autoimmune neuromuscular disorders (e.g., myositis, inflammatory neuropathy) Ref Harrison 20th edition page3238, 3239 (table 440-4)