Which of the following drugs is contraindicated in myasthenia gravis?
Procyclidine (D) is an antimuscarinic (anticholinergic) agent used in Parkinson’s disease as well as to treat the parkinsonian (extrapyramidal) side effects of antipsychotic medication. Myaesthenia gravis (MG) is an autoimmune neurological disorder caused by circulating antibodies against acetylcholine receptors at the postsynaptic neuromuscular junction. Any drugs that inhibit acetylcholine (such as anticholinergics) will worsen the symptoms of MG. Chlorpromazine (A) is a first-generation antipsychotic.
It should be used with caution in patients with MG as it does have anticholinergic properties. However, it is not contraindicated as such. Citalopram (B) is an SSRI. It has potent effects at the 5-HT1A receptor but minimal activity at muscarinic receptors (although note not zero activity).
Galantamine (C) is an AChEI used in the management of Alzheimer’s disease. It increases the availability of acetylcholine so in theory should improve the symptoms of MG, although it does not have a license for this in the UK.
Pyridostigmine (E) is another AChEI, but in this case is used in the treatment of MG and in fact is one of the mainstays of treatment.