A physician diagnoses a client with myasthenia gravis, prescribing pyridostigmine (Mestinon), 60 mg P.O. every 3 hours. Before administering this anticholinesterase agent, the nurse reviews the client’s history. Which preexisting condition would contraindicate the use of pyridostigmine?
A. Ulcerative colitis
B. Blood dyscrasia
C. Intestinal obstruction
D. Spinal cord injury
Correct Answer: C. Intestinal obstruction
Anticholinesterase agents such as pyridostigmine are contraindicated in a client with a mechanical obstruction of the intestines or urinary tract, peritonitis, or hypersensitivity to anticholinesterase agents. Pyridostigmine bromide is preferred over neostigmine because of its longer duration of action. In those with bromide intolerance that leads to gastrointestinal effects, ambenonium chloride can be used. Patients with MuSK MG respond poorly to these drugs and hence may require higher doses.
Option A: Ulcerative colitis is not a contraindication to pyridostigmine. The mainstay of treatment in MG involves cholinesterase enzyme inhibitors and immunosuppressive agents. Symptoms that are resistant to primary treatment modalities or those requiring rapid resolution of symptoms (myasthenic crisis), plasmapheresis, or intravenous immunoglobulins can be used.
Option B: Blood dyscrasia is not a contraindication to pyridostigmine. Agricultural employees who handle organophosphates for a prolonged period should have medical monitoring. Appropriate testing is recommended to identify overexposure before the occurrence of clinical illness. Both serum and RBC cholinesterase must be determined.
Option D: The contraction of the smooth muscle in various organs of the body gets mediated through M3 receptors. Tone and peristalsis in the gastrointestinal tract increase and sphincters relax, causing abdominal cramps and evacuation of the bowel. The detrusor muscle contracts while the bladder trigone and sphincter relax, leading to the voiding of the bladder.
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