Last updated Jan. 20, 2022, by Marisa Wexler, MS
Fact-checked by Joana Carvalho, PhD
Mestinon (pyridostigmine) is an oral medicine used to improve muscle strength in people with myasthenia gravis (MG). It has been approved by the U.S. Food and Drug Administration since 1955.
The name-brand medication is manufactured by Bausch Health, formerly known as Valeant Pharmaceuticals. Generic versions of Mestinon also have been approved and are available in syrup, tablet, and injection forms.
How does Mestinon work?
MG is an autoimmune disorder in which the immune system produces self-reactive antibodies that mistakenly attack the connections between nerves and muscle cells, disrupting communication between the two systems. The ultimate result is muscle weakness.
Nerve cells communicate with muscle cells by releasing a signaling molecule, or neurotransmitter, called acetylcholine, which binds to receptors on muscle cells. Most cases of MG are driven by antibodies that target the acetylcholine receptor.
Unbound acetylcholine is gradually destroyed by an enzyme called acetylcholinesterase. Mestinon is an acetylcholinesterase inhibitor and works by preventing the destruction of acetylcholine by this enzyme. By blocking the destruction of acetylcholine, Mestinon ensures that more of the neurotransmitter can bind to the remaining acetylcholine receptors on muscle cells, thereby improving nerve-muscle communication and muscle strength.
Mestinon in clinical research
Mestinon was developed more than half a century ago when the modern concept of clinical trials did not exist. The evidence for its effectiveness mostly comes from retrospective studies and clinical experience. These studies have shown an objective and marked clinical effect of Mestinon, as well as a good safety profile in MG patients.
The therapy is used as a first-line treatment for all MG forms. It also is considered suitable as a long-term treatment in patients with generalized, non-progressive, and milder forms of MG, and as an add-on therapy in people with severe disease who also are receiving immune-suppressing therapies. However, similar to other acetylcholinesterase inhibitors, it provides only partial and temporary benefits, with most patients also requiring treatments that suppress the immune system.
Mestinon is available in tablet or syrup formulations. The exact dosage of the medication is tailored based on the needs of the individual being treated.
The most common side effects associated with Mestinon include nausea, diarrhea, vomiting, abdominal cramps, upset stomach, excessive sweating, muscle cramps, and muscle weakness.
Mestinon is contraindicated, or should not be used, in people who have mechanical obstructions of the digestive or urinary tracts. Caution is recommended when using the medication to treat people with asthma.
A too-high dosage of Mestinon or similar medications can result in a cholinergic crisis — a condition in which muscle cells are overstimulated by acetylcholine, resulting in muscle weakness. Importantly, cholinergic crises can appear very similar to an episode of MG worsening, but the cause — and, therefore, the necessary treatment — is different, so it is important to distinguish between the two.
A medication called atropine may be useful for reversing cholinergic crisis and lessening the digestive side effects of Mestinon. However, caution is recommended when combining these medications since treatment with atropine can mask signs of a cholinergic crisis that may require medical attention.
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