Pyridostigmine
Pyridostigmine bromide
Also known as: Mestinon · Distinon · Kalymin · Regonol · pyridostigmini bromidum · Pyridostigmine bromide
Reviewed by the VetSheet Veterinary TeamUpdated Apr 5, 2026Evidence-based veterinary reference
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Dosing by species
🌎 NA — North America🌍 EU — Europe
Dogs
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Myasthenia gravis (MG) | 1-3 mg/kg PO q8-12h. For animals that cannot tolerate oral medications, it may be used as an IV constant rate infusion at 0.01-0.03 mg/kg/hour. | PO/IV | q8-12h or CRI | — | 🌎 NA |
| Myasthenia gravis (MG) | 0.5-3 mg/kg PO q8-12 hours with food. | PO | q8-12h | — | 🌎 NA |
| Acquired Myasthenia gravis (MG) | 7.5-30 mg PO two times a day. | PO | BID | — | 🌎 NA |
| Myasthenia gravis (MG) | 0.5-3 mg/kg PO two to three times a day. | PO | BID-TID | — | 🌎 NA |
| Myasthenia gravis (MG) | 0.5-1 mg/kg PO two to three times a day | PO | BID-TID | — | 🌎 NA |
| Myasthenia gravis | 0.2-5 mg/kg | PO | q8-12h | — | 🌍 EU |
- Myasthenia gravis (MG): Titrate to effect to minimize adverse effects and maximize muscle strength.
- Myasthenia gravis (MG): Start low and increase slowly. Liquid formulation recommended for easy adjustment. An H2 antagonist (e.g., famotidine 5 mg/kg/day) may reduce nausea/GI irritation.
- Acquired Myasthenia gravis (MG): Begin after oral regurgitation is abolished with parenteral neostigmine. Once stable, begin corticosteroids for 2 weeks, then gradually reduce pyridostigmine.
- Myasthenia gravis (MG): If no response, add prednisone.
- Myasthenia gravis (MG): With or without prednisone (2 mg/kg PO twice daily). Spontaneous remission is not uncommon.
- Myasthenia gravis: Dose should be incrementally adjusted to maximize muscle strength and minimize adverse effects.
Cats
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Myasthenia gravis (MG) | 0.5-3 mg/kg daily PO in divided doses | PO | Divided daily | — | 🌎 NA |
| Myasthenia gravis (MG) | 1-3 mg/kg PO q8-12h | PO | q8-12h | — | 🌎 NA |
| Myasthenia gravis (MG) | 0.5-3 mg/kg PO per day | PO | Daily | — | 🌎 NA |
| Myasthenia gravis | 0.25 mg/kg | PO | q8-12h | — | 🌍 EU |
- Myasthenia gravis (MG): Dose depending on response.
- Myasthenia gravis (MG): Given with corticosteroids.
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Overview
Pyridostigmine bromide is a synthetic quaternary ammonium anticholinesterase agent primarily used in veterinary medicine for the management of myasthenia gravis (MG) in dogs, and less commonly in cats.
- Clinical Pearl: Because of its quaternary ammonium structure, pyridostigmine is highly ionized and does not readily cross the blood-brain barrier at standard therapeutic doses. This makes it ideal for targeting peripheral neuromuscular junction disorders like MG without causing significant central nervous system (CNS) side effects.
- It is generally considered much more effective for acquired myasthenia gravis compared to the congenital form of the disease.
- Due to its erratic absorption and narrow therapeutic index, dosing must be carefully titrated to effect, balancing improved muscle strength against the risk of cholinergic toxicity.
Mechanism of action
Pyridostigmine acts as a reversible, competitive inhibitor of the enzyme acetylcholinesterase (AChE) at the neuromuscular junction.
- Mechanism: Pyridostigmine competes directly with acetylcholine (ACh) for attachment to AChE. The resulting pyridostigmine-AChE complex is hydrolyzed much more slowly than the natural ACh-AChE complex.
- Pathway: Inhibition of AChE → Decreased breakdown of ACh → Accumulation of ACh in the synaptic cleft → Prolonged and increased stimulation of nicotinic ACh receptors on the motor endplate → Enhanced skeletal muscle contraction and improved strength in myasthenic patients.
Safety & warnings
Contraindications
- Hypersensitivity to anticholinesterase compounds or bromides
- Mechanical or physical obstructions of the urinary tract
- Mechanical or physical obstructions of the gastrointestinal (GI) tract
- Mechanical gastrointestinal obstruction
- Mechanical urinary tract obstruction
- Peritonitis
Adverse effects
- Nausea
- Vomiting
- Diarrhea
- Excessive salivation (ptyalism)
- Sweating (in species with sweat glands)
- Increased bronchial secretions
- Bronchospasm
- Pulmonary edema
- Respiratory paralysis
- Miosis (pupil constriction)
- Blurred vision
- Lacrimation (tearing)
- Bradycardia
- Tachycardia
- Cardiospasm
- Hypotension
- Cardiac arrest
- Muscle cramps
- Weakness (can indicate cholinergic crisis)
- Increased salivation (ptyalism)
- Diarrhoea
- Abdominal cramps
- Bronchoconstriction
- Involuntary defecation and micturition
- Nystagmus
- Heart block
- Arrhythmias
- Agitation
- Muscle weakness
- Fasciculations
Precautions
High-Risk Patients: Use with extreme caution in patients with bronchospastic disease, epilepsy, hyperthyroidism, bradycardia or other arrhythmias, vagotonia, or GI ulcer diseases.
- Pregnancy/Nursing: FDA Category C. Excreted in maternal milk; use with caution in nursing patients.
- Dose Titration: Doses must be carefully titrated. High doses can cause a cholinergic crisis, which presents as profound weakness and can be difficult to distinguish from a myasthenic crisis.
Drug interactions
Antagonizes the muscarinic effects of pyridostigmine. Use cautiously as it can mask early clinical signs of a life-threatening cholinergic crisis.
May decrease the anticholinesterase activity of pyridostigmine. Discontinuing corticosteroids may suddenly increase anticholinesterase activity, requiring dose adjustments.
Theoretically may have additive cholinergic effects when used concurrently.
May necessitate increased dosages of pyridostigmine when treating or diagnosing myasthenic patients.
Can antagonize anticholinesterase therapy due to its direct depressant effect on skeletal muscle.
May prolong the Phase I block of depolarizing muscle relaxants (e.g., succinylcholine) and antagonize the actions of non-depolarizing agents (e.g., pancuronium, atracurium).
May antagonize the neuromuscular effects of pyridostigmine
May antagonize the neuromuscular effects of pyridostigmine
May antagonize the neuromuscular effects of pyridostigmine
May antagonize the effects of pyridostigmine
Pyridostigmine may enhance the effect of depolarizing muscle relaxants
Pyridostigmine antagonizes the effect of non-depolarizing muscle relaxants
Pyridostigmine antagonizes the effect of non-depolarizing muscle relaxants
Monitoring
- Clinical signs of cholinergic toxicity (salivation, lacrimation, urination, defecation, GI upset, emesis, weakness)
- Efficacy of therapy (improvement in muscle strength, reduction of megaesophagus/regurgitation)
- Improvement in muscle strength and exercise tolerance
- Signs of muscarinic toxicity (hypersalivation, vomiting, diarrhea, miosis)
- Heart rate and rhythm
- Respiratory rate and effort (especially in patients with megaoesophagus)
Pharmacokinetics
Absorption
Marginally absorbed from the GI tract. Absorption may be erratic, especially with sustained-release tablets. Onset of action after oral dosing is generally within one hour.
Distribution
Distributed to most tissues, but does not cross into the brain (CNS), intestinal wall, fat, or thymus at usual doses due to its quaternary ammonium structure. Crosses the placenta.
Metabolism
Metabolized by the liver and hydrolyzed by cholinesterases.
Elimination
Excreted primarily via the kidneys (implied by class, though specific veterinary elimination data is sparse in the monograph).
Overdose
Overdosage of pyridostigmine can induce a life-threatening cholinergic crisis.
- Clinical Signs (SLUDGE syndrome): GI effects (nausea, vomiting, diarrhea), excessive salivation, sweating, respiratory distress (increased bronchial secretions, bronchospasm, pulmonary edema, respiratory paralysis), ophthalmic effects (miosis, blurred vision, lacrimation), cardiovascular collapse (bradycardia, tachycardia, hypotension, cardiac arrest), severe muscle cramps, and profound weakness.
- Diagnostic Challenge: Overdoses in myasthenic patients can be very difficult to distinguish from a myasthenic crisis (disease exacerbation). The time of onset of clinical signs or an edrophonium challenge (Tensilon test) may help differentiate the two.
- Treatment: Consists of immediate respiratory and cardiac supportive therapy. Atropine should be administered to antagonize muscarinic effects (refer to atropine protocols for cholinergic toxicity).
Available products
Formulations
- Extended-release tablets
- Injection
- 60 mg tablets
- 60 mg/5 ml oral syrup (available on import licence)
Human-labeled
- Pyridostigmine Bromide Tablets: 60 mg (Mestinon®, generic)
- Pyridostigmine Bromide Extended-Release Tablets: 180 mg (Mestinon®)
- Pyridostigmine Bromide Syrup: 12 mg/mL in 480 mL (Mestinon®)
- Pyridostigmine Bromide Injection: 5 mg/mL in 2 mL ampules (Mestinon®)
- Mestinon 60 mg tablets
Regulatory status
Human registered products often used under the cascade.
POM (Prescription Only Medicine). Oral syrup available on import licence.
No regulatory data for: 🇺🇸 US · 🇭🇰 HK · 🇹🇼 TW · 🇯🇵 JP · 🇰🇷 KR · 🇦🇺 AU
Storage & stability
Store products at room temperature unless otherwise instructed. Protect oral solution and injection from light and freezing. Keep tablets in tight containers. Extended-release tablets may become mottled over time, but this does not affect potency. Injection is unstable in alkaline solutions.
Client information
Pyridostigmine is a crucial medication for managing your pet's myasthenia gravis, but the dose must be very precise.
- Strict Dosing: Give this medication exactly as prescribed by your veterinarian. Do not change the dose without consulting them, as the difference between an effective dose and a toxic dose is very small.
- Administration: Giving the medication with food may help reduce stomach upset. Liquid forms are often preferred to allow for tiny dose adjustments.
- Watch for Toxicity: Contact your veterinarian immediately if you notice signs of an overdose, which include: excessive drooling, vomiting, diarrhea, extreme weakness, muscle twitching, or difficulty breathing.
- Spontaneous Remission: In some dogs, myasthenia gravis can resolve on its own over time, so your vet will monitor your pet closely to see if the medication can eventually be reduced or stopped.
VetSheet drug reference is intended for licensed veterinary professionals as a clinical decision-support aid, not a substitute for professional judgement or the manufacturer’s current label.