Mestinon (pyridostigmine bromide) for myasthenia gravis
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What is Mestinon for myasthenia gravis?
Mestinon (pyridostigmine bromide) is an oral therapy approved for the treatment of myasthenia gravis (MG).
Originally created by Roche in 1945, the brand-name medication is manufactured in North America by Bausch Health, formerly known as Valeant Pharmaceuticals. Generic versions of Mestinon also have been approved and are available in oral forms (syrup and tablets).
Therapy snapshot
| Brand Name: | Mestinon |
| Chemical Name: | Pyridostigmine bromide |
| Usage: | Treatment of myasthenia gravis; can improve muscle strength |
| Administration: | Oral (tablets or syrup) |
How does Mestinon work?
MG is an autoimmune disorder in which the immune system produces self-reactive antibodies that mistakenly attack proteins within the neuromuscular junction — the region where nerves connect with the muscles they control. This leads to the typical MG symptoms of muscle weakness and fatigue.
Most cases of MG are driven by antibodies that target the acetylcholine receptor, a cell surface protein that is activated by acetylcholine, a signaling molecule or neurotransmitter released by nerve cells to communicate with muscle cells.
Part of a group of medications called anticholinesterases or acetylcholinesterase inhibitors, Mestinon works by suppressing the activity of acetylcholinesterase, the enzyme that gradually breaks down unbound acetylcholine.
By preventing the destruction of acetylcholine, Mestinon ensures more of the neurotransmitter can bind to the remaining acetylcholine receptors on muscle cells, improving nerve-muscle communication and enhancing muscle strength.
Who can take Mestinon?
Mestinon was approved by the U.S. Food and Drug Administration for the treatment of MG in 1955 as an oral tablet. Other formulations have been developed since then, including extended-release tablets, syrups, and injectable forms.
Who should not take Mestinon?
Mestinon should not be taken by patients with mechanical obstructions of the digestive or urinary tracts. Patients also should avoid Mestinon if they have a known allergy to the therapy, any of its ingredients (such as bromides), or other anticholinesterase agents.
Caution also is recommended when using the medication to treat people with certain co-existing conditions, such as asthma, seizures, heart disease, kidney problems, thyroid problems, or stomach ulcers.
Like all anticholinesterases, an overdosage of Mestinon can result in a cholinergic crisis — a condition marked by increasing muscle weakness that can also affect muscles involved in breathing. If such a crisis occurs, treatment with Mestinon should be discontinued. In such cases, immediate treatment with atropine is also recommended.
According to the therapy’s prescribing information, its safety and effectiveness have not been established in pediatric patients.
How is Mestinon administered?
Mestinon is available in three oral formulations for the treatment of MG. It can be dispensed as:
- an oral solution of raspberry-flavored syrup, in which each teaspoonful (5 mL) contains 60 mg of Mestinon
- white, flat-faced conventional tablets, each containing 60 mg of the medication’s active ingredient
- light straw-colored, capsule-shaped Timespan extended-release tablets, with each containing 180 mg of Mestinon.
The exact dosage of the medication is tailored based on the needs of each individual patient.
The average daily dose of Mestinon is 10 conventional 60 mg tablets or 10 teaspoonfuls (5 mL) of syrup. Up to 25 tablets or teaspoonfuls a day may be required in more severe cases, while 1-6 tablets or teaspoonfuls a day may be enough for mild cases.
Mestinon Timespan tablets have an effect that lasts, on average, 2.5 times longer than that of conventional tablets. Thus, from one to three 180 mg tablets, taken once or twice a day, are usually enough to control symptoms. Doses should be separated by at least six hours, and the tablets should not be crushed, chewed, or broken, but swallowed whole. These extended-release tablets are known as Mestinon retard in other countries, such as Germany.
Lower doses may be required in people with kidney problems, in whom optimal treatment doses should be carefully determined based on its effects.
Mestinon in clinical trials
Mestinon was developed and approved decades ago, when the modern concept of clinical trials did not exist. The evidence for its effectiveness mostly comes from small retrospective studies and clinical experience.
Early, small studies mainly compared Mestinon against neostigmine, the gold standard anticholinesterase treatment in MG at the time. Most of them reported that patients found Mestinon to be superior or comparable to neostigmine.
Overall, 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 types of MG. It also is considered suitable as a long-term treatment in people with generalized, nonprogressive, and milder forms of MG, and as an add-on therapy in people with severe disease who also are receiving immunosuppressive therapies.
However, similar to other anticholinesterase agents, it provides only partial and temporary benefits, with most patients also requiring treatments that suppress the immune system.
Timespan extended-release tablets trial
A multicenter trial in Germany — the results of which were published in 2010 — tested the effects of switching from pyridostigmine bromide conventional tablets to Timespan tablets in 72 adults with stable MG. In addition to Timespan, 40.3% of the patients took conventional tablets, most commonly in the morning, to speed treatment effect.
The results showed the treatment switch was unproblematic in all patients, and, as expected, led to a reduction in the number of daily doses. Switching to Timespan tablets for one month also significantly reduced Quantitative MG scale scores, indicating less disease severity, and significantly improved quality of life parameters.
In addition, the therapeutic switch was associated with the complete resolution or with lessening of several adverse events, or side effects, though some new side effects were reported.
Common side effects of Mestinon
Side effects most commonly reported in patients given Mestinon are usually related to overdosage. They may include:
- nausea
- diarrhea
- vomiting
- abdominal cramps
- excessive saliva, tear, or sweat production
- increased production of airway mucus
- excessive contraction of the pupil of the eye
- muscle cramps and twitching
- muscle weakness.
Skin rash also may occur in some patients, as with any medication that contains bromide. These reactions typically resolve rapidly with treatment discontinuation.
Cholinergic crisis
An overdose 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. Cholinergic crises can appear very similar to myasthenic crises, or episodes of MG worsening, but the cause — and, therefore, the necessary treatment — is different, so it is important to distinguish between the two.
In case of a cholinergic crisis, Mestinon should be discontinued and patients should be treated with a medication called atropine to resolve the complication.
Atropine also may be useful for lessening gastrointestinal problems and other Mestinon side effects. However, caution is recommended when combining these medications as treatment with atropine can mask the signs of a cholinergic crisis that may require medical attention.
Use in people with kidney disease
Patients with kidney problems should take a lower dose of Mestinon, as the therapy may take longer to be cleared from the body. The optimal dose of the therapy should be carefully determined for each patient based on its individual effects in that person.
Use in pregnancy and breastfeeding
No adequate and well-controlled studies have been done in patients who are pregnant or breastfeeding while receiving Mestinon. Animal data have suggested the therapy causes no harm to the developing fetus, and small patient studies have suggested that Mestinon is generally safe when taken during pregnancy and that it is found at negligible amounts in breast milk.
However, as with all treatments, patients who are pregnant or nursing, planning to become pregnant or breastfeed while on the medication should discuss this topic with their healthcare providers.
Myasthenia Gravis News is strictly a news and information website about the disease. It does not provide medical advice, diagnosis, or treatment. This content is not intended to be a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition. Never disregard professional medical advice or delay in seeking it because of something you have read on this website.
FAQs about Mestinon
The U.S. Food and Drug Administration (FDA) approved Mestinon in 1955 as an oral tablet for the treatment of myasthenia gravis. Other formulations have been developed since then, including extended-release tablets, syrups, and injectable forms.
As each person is unique and can respond differently to treatment, there is no standard timeline for when Mestinon starts to work. But the therapy has been reported to take about 20-30 minutes to have a clinical effect. Mestinon’s therapeutic effects last for approximately six hours in the case of conventional tablets, and six to 12 hours in the case of Timespan extended-release tablets. Still, patients are advised to talk with their healthcare team to understand how Mestinon can help in their particular case.
No well-controlled studies of Mestinon have included pregnant patients, so it is unclear whether the therapy is safe to use during pregnancy. Patients who are pregnant or plan to become pregnant while on Mestinon should discuss this with their doctor.
Because Mestinon can increase the contraction of the eye’s pupil, it may cause blurred vision and reduce the sharpness of a person’s eyesight. Patients are advised not to drive or operate machines until they know how the therapy affects their vision, and to avoid these activities altogether if it does reduce their ability to see clearly.
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