Switching between neostigmine and pyridostigmine in myasthenia gravis

Switching between neostigmine and pyridostigmine in myasthenia gravis

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In some cases, the prescriber may wish to switch between oral pyridostigmine and parenteral neostigmine e.g. due to swallowing difficulties caused by worsening of myasthenia gravis (1). As symptoms of myasthenia gravis improve, a switch to an oral formulation may be preferred

In the UK available formulations are:

• neostigmine- parenteral injections
• pyridostigmine- oral solution or tablets

A review notes (2):

• neostigmine - is useful in patients with myasthenia gravis who cannot absorb via the oral route (e.g., a myasthenia gravis patient with acute bowel obstruction) but should not be first line if the patient has impaired swallow
  • swallowing difficulties are very common in patients with myasthenia gravis and if there are concerns about aspiration with oral intake, including medications, the first strategy should always be to place a nasogastric tube and administer pyridostigmine via this
    • only if this cannot be undertaken should subcutaneous neostigmine be used
  • has the same side effect profile as pyridostigmine albeit with more marked cardioinhibitory effects and a shorter half-life leading to more frequent dosing
  • neostigmine should always be used with caution since it may cause excessive salivary secretions and as a result may further negatively impact and exacerbate swallowing difficulties

Dosing equivalence:

• 60mg oral pyridostigmine is equivalent to 1 to 1.5mg intramuscular or subcutaneous neostigmine (1)

Example of switch from oral pyridostigmine to subcutaneous neostigmine:

• a 30-year-old lady takes 60mg pyridostigmine four times a day for myasthenia gravis. The prescriber would like to switch to subcutaneous neostigmine. The method of calculating the subcutaneous neostigmine dose is as follows:
  • 60mg pyridostigmine is equivalent to 1 or 1.5mg subcutaneous neostigmine
  • suitable regimen for this individual could be 1mg neostigmine subcutaneous injection given four times a day

Example switch from subcutaneous neostigmine to oral pyridostigmine (3)

• a 60-year-old man uses 1.7mg subcutaneous neostigmine injection 5 times a day for myasthenia gravis. You would like to switch the individual to oral pyridostigmine. The method of calculating the oral pyridostigmine dose is as follows:
  • 1 or 1.5mg subcutaneous neostigmine injection is approximately equivalent to 60mg oral pyridostigmine
  • using the higher dose of 1.5mg neostigmine as approximately equivalent to 60mg oral pyridostigmine, the 1.7mg subcutaneous neostigmine injection is approximately equivalent to 68mg oral pyridostigmine
  • based on a dosing frequency of 5 times a day, this equates to 340mg oral pyridostigmine over 24 hours
• a suitable regimen for this individual could be 90mg oral pyridostigmine in the morning, followed by 4 doses of 60mg oral pyridostigmine in a day

Notes:

• pyridostigmine has a slower onset of action and longer duration of action versus neostigmine so the dosing interval of pyridostigmine may be longer compared to neostigmine
• time critical dosing
  • medicines for MG are time critical and must be given on time or within 2 hours of the prescribed dose.
  • excessive weakness and difficulty in breathing and swallowing may arise if medicines for myasthenia gravis are administered too late.
  • missing or delaying doses can lead to myasthenic crisis, which can be fatal
  • maintaining the prescribed dosing schedule is essential

Reference:

1. NHS Specialist Pharmacy Service (October 2022). Switching between neostigmine and pyridostigmine in myasthenia gravis
2. Farrugia ME, Goodfellow JA. A Practical Approach to Managing Patients With Myasthenia Gravis-Opinions and a Review of the Literature. Front Neurol. 2020 Jul 7;11:604
3. NHS Specialist Pharmacy Service (January 2026). Switching between pyridostigmine and neostigmine.