In theory, more than 30 drugs currently used for many different conditions can interfere with nerve → muscle transmission. Nature has made the ignition system very secure. Normally there is such a safety factor that, even if a drug interferes by up to 50 per cent, there is still enough in reserve to prevent any weakness. The problem in myasthenia is that the reserves are low. Only a very slight further dip in transmission can make things a lot worse.

The one exceptional drug that must be avoided in myasthenias is the ketolide antibiotic, Telithromycin (Ketek) which has caused deaths.

Download our PDF of medication that can make myasthenia worse; included within the PDF are some very important general guidelines. 

Download the NHS Scotlandlist of contraindicated medicines, due for renewal soon.

Drugs Used in Neurology and Psychiatry

These drugs are used for a wide range of neurological and psychiatric disorders. For most of them, the evidence that they cause problems in myasthenia is limited and none are absolutely banned. It is sensible to be cautious, as with all new prescriptions.

Penicillamine

Typical myasthenia can appear in some rheumatoid arthritis patients who are treated with the drug penicillamine. This is therefore best avoided.

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Please note that these drugs to avoid are listed in relation to myasthenia gravis only and not CMS or LEMS.