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Pyridostigmine (Mestinon®)

By: Dr. Nicholas Dodman

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  • Pyridostigmine is an anticholinesterase drug that is used for the treatment of myasthenia gravis and for the reversal of non-depolarizing neuromuscular blocking drugs.
  • Pyridostigmine belongs to a class of drugs called cholinesterase inhibitors.
  • Pyridostigmine inhibits acetylcholine by competing for the enzyme acetylcholinesterase. This competition leads to increased concentrations of acetylcholine and attachment to specific neuromuscular receptors which allows the muscles to contract normally.
  • Pyridostigmine is a prescription drug and can only be obtained from a veterinarian or by prescription from a veterinarian.
  • This drug is not approved for use in animals by the Food and Drug Administration but it is prescribed legally by veterinarians as an extra-label drug.

    Brand Names and Other Names

  • This drug is registered for use in humans only.
  • Human formulations: Mestinon® (ICN) and generic pyridostigmine bromide.
  • Veterinary formulations: None

    Uses of Pyridostigmine

    Pyridostigmine is used for:

  • Treatment of myasthenia gravis
  • Reversal of non-depolarizing muscle relaxants

    Precautions and Side Effects

  • While generally safe and effective when prescribed by a veterinarian, pyridostigmine can cause side effects in some animals.
  • Pyridostigmine should not be used in animals with known hypersensitivity or allergy to the drug or bromides.
  • Pyridostigmine should not be used in pregnant animals.
  • It is also contraindicated when there is mechanical obstruction of the intestinal or urinary tract.
  • Pyridostigmine should be used with caution in patients prone to bronchospasm, bradycardia, A-V block, vagotonia, hyperthyroidism, or peptic ulceration.
  • Overdose of pyridostigmine may lead to cholinergic crisis, with increasing muscle weakness.

    Drug Interactions

    Pyridostigmine may interact with other medications. Consult with your veterinarian to determine if other drugs your pet is receiving could interact with pyridostigmine. Such interactions may include:

  • Pyridostigmine may prolong the neuromuscular block produced by succinylcholine
  • Methocarbamol may impair the effect of pyridostigmine in myasthenic patients
  • Magnesium has a direct depressant effect on skeletal muscle and may counteract the beneficial effects of pyridostigmine
  • Aminoglycoside antibiotics have a mild non-depolarizing effect that can counter the effect of pyridostigmine in myasthenia gravis
  • Corticosteroids may decrease the effectiveness of pyridostigmine
  • Local anesthetics should be used cautiously, if at all, in treated or untreated myasthenic patients

    How Pyridostigmine is Supplied

  • Pyridostigmine is available in 60 mg tablets and 180 mg extended-release tablets.
  • Pyridostigmine 60 mg/5mL (in 480 mL bottle) mg/ml syrup is available.
  • The injectable form includes a 5 mg/mL (in 2 mL amps) concentration.

    Dosing Information

  • Medication should never be administered without first consulting your veterinarian.
  • The dosage prescribed may vary depending on the reason for prescribing.
  • The duration of administration depends on the condition being treated, response to the medication and the development of any adverse effects. Be certain to complete the prescription unless specifically directed by your veterinarian. Even if your pet feels better, the entire treatment plan should be completed to prevent relapse.
  • In dogs, the usual dose for treatment of myasthenia gravis is 0.25 to 1.5 mg per pound (0.5 to 3 mg/kg) orally every 8 to 12 hours.
  • In cats, the usual dose for treatment of myasthenia gravis is 0.125 mg per pound (0.25 mg/kg) orally per day. The dose can be slowly increased to 0.5 to 1.5 mg per pound (1 to 3 mg/kg) orally every 8 to 12 hours as necessary.

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