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Switching between neostigmine and pyridostigmine in myasthenia gravis

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Topics: NeostigminePyridostigmineSwitching

Switching between neostigmine and pyridostigmine requires care and application of a stepped process

Contents
  1. Reason for switching
  2. Considerations for switching
    1. Formulations available
    2. Licensing
    3. Dosing equivalence
    4. Clinical considerations
    5. Duration of action
  3. Switching from pyridostigmine to neostigmine
    1. Determine the pyridostigmine dose
    2. Convert to neostigmine
    3. Give and repeat dose
    4. Worked example
  4. Switching from neostigmine to pyridostigmine
    1. Determine the neostigmine dose
    2. Convert to pyridostigmine
    3. Give and repeat dose
    4. Worked example
  5. Monitoring after the switch

Reason for switching

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. As symptoms of myasthenia gravis improve, a switch to an oral formulation may be preferred. 

Considerations for switching

Consider the following points before switching between formulations.

Formulations available

The available formulations are:
  • neostigmine- parenteral injections
  • pyridostigmine- oral solution or tablets

Licensing

Neostigmine formulations are licensed for different therapeutic indications.

  • Intramuscular or subcutaneous neostigmine is licensed for myasthenia gravis.
  • Intravenous neostigmine is licensed for reversal of non-depolarising neuromuscular blockage. This route will not be covered as this page focuses on switching between neostigmine and pyridostigmine in myasthenia gravis.

All oral formulations of pyridostigmine are licensed for myasthenia gravis. Use pyridostigmine liquid in people with swallowing difficulty or enteral feeding tubes.

Dosing equivalence

60mg oral pyridostigmine is equivalent to 1 to 1.5mg intramuscular or subcutaneous neostigmine.

Clinical considerations

  • The prescribed dose of parenteral neostigmine or oral pyridostigmine for myasthenia gravis is correct.
  • The healthcare professional has considered factors affecting the choice of the medicine (for example: cautions, contraindications and medicine interactions).
  • The individual is aged 12 years or over.

Duration of action

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.

Switching from pyridostigmine to neostigmine

There are no formal studies on switching from oral pyridostigmine to parenteral neostigmine. The switching advice below is based on established dosing equivalence referenced in standard medical literature.

Worked example

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.

A suitable regimen for this individual could be 1mg neostigmine subcutaneous injection given four times a day.

Switching from neostigmine to pyridostigmine

There are no formal studies on switching from parenteral neostigmine to oral pyridostigmine. The switching advice below is based on established dosing equivalence referenced in standard medical literature.

Worked example

A 60-year-old man uses 1.5mg subcutaneous neostigmine five times a day for myasthenia gravis. The prescriber 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 is equivalent to 60mg pyridostigmine.

A suitable regimen for this individual could be 60mg pyridostigmine given five times a day.

Monitoring after the switch

Monitor the individual closely after the switch to ensure the symptoms of myasthenia gravis are appropriately controlled and side effects are tolerable. Doses should be adjusted accordingly.

The healthcare professional initiating the switch should assess the individual and consider any additional monitoring on case-by-case basis.