Mestinon Drug Interactions You Need to Know About

If you're taking Mestinon (Pyridostigmine Bromide), it's important to understand how it interacts with other medications. Some drug interactions can reduce Mestinon's effectiveness, while others can increase the risk of serious side effects.

This guide covers the major and moderate interactions, supplements to watch out for, and what to tell your doctor before starting or changing any medications.

How Drug Interactions Work with Mestinon

Mestinon is a cholinesterase inhibitor — it works by increasing levels of acetylcholine in your body. Drug interactions with Mestinon generally fall into two categories:

1. Drugs that oppose Mestinon's effects — These reduce acetylcholine activity, making Mestinon less effective. Anticholinergic drugs are the main culprits.
2. Drugs that add to Mestinon's effects — These also increase acetylcholine or affect the neuromuscular junction, raising the risk of excessive cholinergic stimulation and side effects.

Major Drug Interactions

These interactions are the most clinically significant. Your doctor needs to know about them before prescribing Mestinon.

Corticosteroids (Prednisone, Methylprednisolone, Dexamethasone)

This is one of the most important interactions for myasthenia gravis patients. When corticosteroids are started in patients already taking Mestinon, they can cause a temporary but severe worsening of muscle weakness — sometimes dramatic enough to require hospitalization. This doesn't mean the two can't be used together (many MG patients take both), but the corticosteroid should be started at a low dose and increased gradually under close medical supervision.

Succinylcholine

Succinylcholine is a muscle relaxant used during surgery. Mestinon can prolong the effects of succinylcholine, leading to extended muscle paralysis. If you're scheduled for surgery, make sure your anesthesiologist knows you take Mestinon.

Aminoglycoside Antibiotics

Antibiotics like Gentamicin, Tobramycin, Amikacin, and Neomycin can interfere with neuromuscular transmission and worsen myasthenia gravis symptoms. When combined with Mestinon, the net effect may be reduced muscle strength. If you need an antibiotic, your doctor should choose one that doesn't affect the neuromuscular junction.

Magnesium

Magnesium — whether given intravenously in the hospital or taken as a supplement — can antagonize the effects of Pyridostigmine. Magnesium blocks acetylcholine release at the neuromuscular junction, directly opposing what Mestinon is trying to do. This is especially important during hospital stays, where IV magnesium is commonly given.

Anticholinergic Medications

Drugs with anticholinergic properties directly reduce acetylcholine activity, which can cancel out Mestinon's effects. Common examples include:

• Atropine — Sometimes used alongside Mestinon to manage GI side effects, but it reduces the drug's effectiveness if used excessively
• Glycopyrrolate (Robinul) — Another anticholinergic used for secretion management
• Oxybutynin (Ditropan) — Used for overactive bladder
• Diphenhydramine (Benadryl) — The common antihistamine has strong anticholinergic effects
• Tricyclic antidepressants like Amitriptyline (Elavil) — Have significant anticholinergic properties

Moderate Drug Interactions

These interactions are worth monitoring but may not require avoiding the combination entirely.

Beta-Blockers

Medications like Metoprolol (Lopressor), Atenolol (Tenormin), and Propranolol (Inderal) can increase the risk of bradycardia (slow heart rate) when combined with Mestinon. Both drugs slow the heart through different mechanisms. If you take a beta-blocker and Mestinon together, your doctor may want to monitor your heart rate more closely.

Quinidine and Procainamide

These antiarrhythmic medications can antagonize the effects of cholinesterase inhibitors like Mestinon. If you need treatment for a heart rhythm disorder, your doctor should consider alternatives.

Lithium

Lithium, used for bipolar disorder, has been reported to worsen myasthenia gravis symptoms. If you take lithium and are starting Mestinon, your neurologist and psychiatrist should coordinate closely.

Other Cholinesterase Inhibitors

Taking Mestinon alongside other cholinesterase inhibitors like Donepezil (Aricept) or Rivastigmine (Exelon) can cause additive cholinergic effects — meaning more side effects like nausea, diarrhea, bradycardia, and excessive salivation. This combination is generally avoided unless carefully monitored.

Supplements and OTC Medications to Watch

Some over-the-counter products and supplements can interact with Mestinon:

• Magnesium supplements — As noted above, magnesium can reduce Mestinon's effectiveness. If you take a magnesium supplement, talk to your doctor about whether to continue it.
• Diphenhydramine (Benadryl) — Its anticholinergic effects can oppose Mestinon. Consider non-anticholinergic alternatives like Cetirizine (Zyrtec) or Loratadine (Claritin) for allergies.
• Antacids containing magnesium — Products like Maalox or Mylanta contain magnesium hydroxide, which may reduce Mestinon's effects if taken in large amounts.
• Sleep aids containing Diphenhydramine or Doxylamine — Many OTC sleep products (ZzzQuil, Unisom) have anticholinergic properties.

Food and Drink Interactions

Mestinon has no major food interactions. In fact, taking it with food is recommended because it reduces GI side effects like nausea and cramping.

There are no significant interactions with alcohol, caffeine, or grapefruit juice. However, alcohol can worsen fatigue and muscle weakness on its own, so moderation is generally advised for MG patients.

What to Tell Your Doctor

Before starting Mestinon or any time you add a new medication, make sure your doctor and pharmacist know about:

• All prescription medications you take — including those prescribed by other doctors
• Over-the-counter medications — especially antihistamines, antacids, and sleep aids
• Supplements and vitamins — particularly magnesium
• Upcoming surgeries or procedures — because of the interaction with muscle relaxants
• Any herbal products you use

It's a good idea to keep an updated medication list in your wallet or phone. This is especially important if you see multiple specialists, which is common for myasthenia gravis patients.

For more on managing your Mestinon therapy, check out our guides on side effects and dosage information.

Final Thoughts

Mestinon is generally well tolerated, but it does interact with several common medications — including corticosteroids, certain antibiotics, magnesium, and anticholinergic drugs. The good news is that most of these interactions are manageable when your healthcare team knows about them.

The most important thing you can do is keep an open line of communication with your doctor and pharmacist. Don't start, stop, or change any medication without checking whether it could affect your Mestinon therapy.

If you're having trouble finding Mestinon at your pharmacy, Medfinder can help you locate it in stock near you.