Switching between pyridostigmine and neostigmine

Reason for switching

Pyridostigmine and neostigmine are licensed for the management of Myasthenia Gravis (MG). If a person with MG has difficulty swallowing due to worsening symptoms, neostigmine injection may be more suitable.

When symptoms improve, switching back to oral pyridostigmine may be appropriate.

Considerations before switching

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 MG are administered too late.

Missing or delaying doses can lead to myasthenic crisis, which can be fatal. Maintaining the prescribed dosing schedule is essential.

Risk of overdosing

Confirm the dose before administering pyridostigmine or neostigmine. Overdosing on these medicines may trigger life-threatening cholinergic crisis. See the overdose section for pyridostigmine and neostigmine in the SmPC.

Formulations

Pyridostigmine and neostigmine are available in different formulations and have different indications.

A 60mg oral pyridostigmine dose is approximately equivalent to 1 to 1.5mg of neostigmine given by intramuscular or subcutaneous injection.

Duration of action

Pyridostigmine has a slower onset and longer duration of action compared to neostigmine. This allows for a longer dosing interval.

Switching from pyridostigmine to neostigmine

There are no formal studies on switching from oral pyridostigmine to neostigmine injection.

Our steps below are based on calculated dose equivalences from standard medical references.

Worked example

A 30-year-old lady takes 60mg oral pyridostigmine 4 times a day for MG. You would like to switch to subcutaneous neostigmine injection. The method of calculating the subcutaneous neostigmine injection dose is as follows:

60mg oral pyridostigmine is approximately equivalent to 1 to 1.5mg subcutaneous neostigmine injection.

A suitable regimen for this individual could be 1mg subcutaneous neostigmine injection given 4 times a day.

Switching from neostigmine to pyridostigmine

There are no formal studies on switching from neostigmine injection to oral pyridostigmine.

Our steps below are based on calculated dose equivalences from standard medical references.

Worked example

A 60-year-old man uses 1.7mg subcutaneous neostigmine injection 5 times a day for MG. 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.

Swallowing difficulties and feeding tubes

Some individuals with MG have swallowing difficulties, or may receive their medicines via an enteral feeding tube.

Use the oral solution of pyridostigmine in individuals with swallowing difficulties or enteral feeding tubes. The oral solution is licensed for administration through a nasogastric or PEG tube. Administering a medicine through an enteral feeding tube (SPS page) outlines points to consider before doing this.

If this is not available, pyridostigmine tablets can be crushed and mixed with water for administration (off label). This can be administered orally or via an enteral feeding tube. Read our guidance on Advising how to crush or disperse tablets and open capsules (SPS page).

Pyridostigmine 60mg tablets can be halved or quartered for part doses if needed.

Monitoring after the switch

Monitor the individual closely after the switch to ensure symptoms of MG are controlled and side effects managed. Worsening symptoms include muscle weakness and difficulty swallowing and are discussed in the NHS article on MG.

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