Switching between neostigmine and pyridostigmine in myasthenia gravis

Switching between neostigmine and pyridostigmine in myasthenia gravis

Seek expert advice.

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:

• 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

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

Reference:

• NHS Specialist Pharmacy Service (October 2022). Switching between neostigmine and pyridostigmine in myasthenia gravis
• 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