Mestinon (pyridostigmine) is a medicine used to treat people with myasthenia gravis. It is being manufactured by Valeant Pharmaceuticals and has been approved by the U.S. Food and Drug Administration (FDA) since 1955. Generic versions of Mestinon also have been approved.
How Mestinon works
Myasthenia gravis is an autoimmune disorder in which the immune system mistakenly attacks the connections between nerve cells and muscle cells disrupting communication between the two systems. The ultimate result is muscle weakness.
Nerve cells release a chemical signaling compound or neurotransmitter called acetylcholine. In people with myasthenia gravis, the immune system attacks receptors found on the muscle cells to which acetylcholine should bind. Unbound acetylcholine is gradually destroyed by the enzyme acetylcholinesterase.
Mestinon is an acetylcholine esterase inhibitor and works by preventing the destruction of acetylcholine by this enzyme. This way, Mestinon ensures that more acetylcholine that can bind to the remaining acetylcholine receptors on muscle cells is available. This counteracts the blockage of acetylcholine receptors caused by the disease and helps strengthen muscles.
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 patients with myasthenia gravis.
Mestinon is used as the first-line treatment for all forms of myasthenia gravis. It also is considered suitable as a long-term treatment in patients with generalized, non-progressive, and milder forms of myasthenia gravis, and as an add-on therapy in patients with severe disease who also are receiving immunotherapy. However, similar to other acetylcholinesterase inhibitors, it provides only partial and temporary benefits, and most patients also require treatments that suppress the immune system.
Mestinon is generally most effective in ocular myasthenia gravis. It is less effective for the treatment of double vision and related motility complaints. Mestinon also is useful for the temporary management transient neonatal myasthenia gravis.
Some possible side effects of Mestinon include nausea, vomiting, diarrhea, increased salivation or drooling, increased sweating, muscle and abdominal cramps, and headache. Some susceptible patients also may experience hypersensitivity reactions.
A new treatment called GTP-004, which combines Mestinon with a medicine called Zofran, is being tested in clinical trials. Zofran is used to prevent nausea and vomiting caused by surgery and cancer treatment. It is hoped that the combination therapy can reduce Mestinon’s gastrointestinal side effects without compromising in effectiveness.
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