Drug-induced myasthenic syndromes.

More than 40 drugs are known to increase muscle relaxation, to aggravate myasthenia gravis, or to induce myasthenic syndromes in "normal" individuals with or without a known impaired safety factor. Many of these drugs have been known for a long time. In the last ten years some other drugs have been added to the long list: Penicillamine, beta-adrenergic blockers, carnitine, some antibiotics, lithium carbonate, catharactics containing magnesium salts, etc. An immunological basis for the penicillamine-induced myasthenia gravis is generally approved, but there may be other examples such as trimethadione and phenytoin. The knowledge of these possible side effects is important for the interpretation of unwanted effects, particularly diplopia and other mild myasthenic symptoms.