Myasthenia gravis is an autoimmune disorder caused by antibodies that bind to and destroy acetylcholine receptors on the surface of skeletal muscle cells, resulting in fatigue and muscle weakness due to impaired muscle contractions.
Although there’s no cure, certain medications, called acetylcholinesterase inhibitors, can be used to help mitigate some of the symptoms and improve the client’s quality of life.
Now, the most commonly used acetylcholinesterase inhibitors for myasthenia gravis are neostigmine and pyridostigmine. These medications can be administered orally, intravenously, or intramuscularly, while neostigmine can be also given subcutaneously to children.
Once absorbed into the bloodstream, acetylcholinesterase inhibitors travel to the skeletal muscles and inhibit the enzyme acetylcholinesterase, which normally breaks down the neurotransmitter acetylcholine.
As a result, these medications cause acetylcholine to build up in the synaptic cleft, causing its cholinergic effects to be increased and prolonged.
This helps counteract the effect of acetylcholine receptor antibodies, and ultimately results in improved muscle strength and contraction.
However, increased acetylcholine levels can also cause cholinergic side effects, such as miosis, blurred vision, headaches, dizziness, and drowsiness.
At the same time, in the airways, acetylcholine triggers bronchoconstriction and increases bronchial secretions, which can lead to dyspnea and a persistent cough.
In the cardiovascular system, acetylcholine reduces blood pressure and slows down the heart rate, which can result in hypotension, bradycardia, heart block, and even cardiac arrest.
In the gastrointestinal tract, these medications can cause increased motility and secretions, leading to increased salivation, nausea, vomiting, cramps, diarrhea, and involuntary defecation;
and in the urinary tract, acetylcholine stimulates the bladder muscles and sphincter relaxation, which may cause a sense of urgency.
Finally, excessive cholinergic stimulation can lead to a cholinergic crisis, which can be managed with atropine.
As far as contraindications go, acetylcholinesterase inhibitors should not be administered to clients with bradycardia, as well as in those with gastrointestinal or urinary obstruction.
Acetylcholinesterase inhibitors should also be used with caution during pregnancy and breastfeeding, as well as in clients with a history of seizures.
Additional precautions should be taken in clients with asthma or chronic obstructive pulmonary disease, as well as in those with cardiovascular disease like arrhythmias, hyperthyroidism, and in clients with gastrointestinal disease like peptic ulcer.
Now, if a client with myasthenia gravis is prescribed an acetylcholinesterase inhibitor like neostigmine, first, perform a baseline assessment, including vital signs and their current symptoms, including fatigue, eyelid drooping, vision problems, peripheral muscle weakness, as well as any difficulty breathing or swallowing.
