Medicines Q&As
Q&A 248.2
How do you convert an oral pyridostigmine dose to a parenteral
neostigmine dose?
Prepared by UK Medicines Information (UKMi) pharmacists for NHS healthcare professionals
Before using this Q&A, read the disclaimer at www.ukmi.nhs.uk/activities/medicinesQAs/default.asp
Published: January 2012
Background
Pyridostigmine is a reversible inhibitor of the enzyme cholinesterase with actions similar to those of
neostigmine, but is slower in onset and has a longer duration of action.(1;2) Both pyridostigmine and
neostigmine are licensed for the treatment of myasthenia gravis: pyridostigmine is given orally whilst
neostigmine can be administered parenterally.(2;3) The dose of pyridostigmine can vary from 30 120mg every 3-4 hours, with between 5-20 tablets taken daily.(2) The total daily dose of neostigmine
can vary between 5-20mg, with 1-2.5mg given by intramuscular (IM) or subcutaneous (SC) injection
every 2-4 hours.(3) Higher doses may be needed in some patients. (2;3) Patients with myasthenia
gravis suffer with weak and easily fatigued muscles, including those of the proximal limbs, extraocular
muscles and the muscles of mastication, speech and facial expression.(4) Dysphagia can occur: if
the patient is unable to swallow but requires anticholinesterases, parenteral neostigmine may be
substituted for pyridostigmine, but how is the dose conversion carried out?
Answer
No formal guidelines for switching between oral pyridostigmine to parenteral neostigmine and no
studies discussing the switch have been identified in the medical literature.




Intravenous doses of pyridostigmine and of neostigmine are about one-thirtieth (1/30) of the
usual oral doses.(1;5)
An oral dose of 15mg neostigmine is equivalent to 1.0 to 1.5mg neostigmine given by
intramuscular (IM) or subcutaneous (SC) injection, or 500 micrograms neostigmine given
intravenously (IV).(5-7)
The potency ratio of IV pyridostigmine to IV neostigmine has been estimated to be 4.35 to 1.(5;8)
So an IV dose of 500micrograms neostigmine is approximately equivalent to 2000micrograms
(2mg) of IV pyridostigmine [4 x 500mcg].
The 2mg IV pyridostigmine dose is 1/30th of the oral dose.(1) It therefore follows that 60mg [30 x
2mg] pyridostigmine given orally is equivalent to approximately 500 microgram neostigmine IV
and 1-1.5mg neostigmine IM or SC.
Calculations:
Drug
Route
Dose
Equivalent to:
Neostigmine
Oral
15mg
 500micrograms Intravenous (IV) (1/30th of the oral dose)
 1mg to 1.5mg Intramuscular (IM) or Subcutaneous (SC)
IV
2000microgram
(2mg)
 Potency ratio of IV pyridostigmine to IV neostigmine is
approximately 4.35:1
 Therefore 500mcg of IV neostigmine is approximately equivalent
to 500x4.35 = 2175 micrograms of IV pyridostigmine
30 x 2mg =
60mg
 IV dose is approximately 1/30th of the oral dose.
 Therefore an IV dose of 2mg pyridostigmine is approximately
equivalent to 30x2mg = 60mg.
 This is equivalent to 500mcg neostigmine IV, or 1mg to 1.5mg IM
or SC.
Pyridostigmine
Pyridostigmine
Oral
From the NHS Evidence website www.evidence.nhs.uk
1
Medicines Q&As
Patients who have their oral dose of pyridostigmine converted to a parenteral dose of neostigmine
should be monitored closely to ensure that the neostigmine is adequately controlling their symptoms
of myasthenia gravis and not causing untoward side effects. Doses should be adjusted accordingly.
Summary



There is no direct conversion of oral pyridostigmine to parenteral neostigmine.
60mg pyridostigmine oral is approximately equivalent to 500 microgram neostigmine IV and 1-1.5
mg neostigmine IM or SC.
Patients who have their oral dose of pyridostigmine converted to a parenteral dose of
neostigmine should be monitored closely to ensure that the neostigmine is adequately controlling
their symptoms of myasthenia gravis and not causing untoward side effects. Doses should be
adjusted accordingly.
Limitations
There are no formal studies which look at the direct conversion between oral pyridostigmine and
parenteral neostigmine.
Disclaimer
 Medicines Q&As are intended for healthcare professionals and reflect UK practice.
 Each Q&A relates only to the clinical scenario described.
 Q&As are believed to accurately reflect the medical literature at the time of writing.
 See NeLM for full disclaimer.
References
(1) Pyridostigmine bromide. Latest modification 10/10/11. Sweetman SC (ed), Martindale: The
Complete Drug Reference [online] London: Pharmaceutical Press
<http://www.medicinescomplete.com/>. Accessed on 30/12/2011.
(2) Summary of Product Characteristics. Mestinon 60mg Tablets, Meda Pharmaceuticals
Accessed via: http://www.emc.medicines.org.uk. Date of access: 30/12/11
(3) Summary of Product Characteristics. Neostigmine Methylsulphate Injection BP 2.5mg in 1ml.
hameln pharmaceuticals ltd. Accessed via:http://www.emc.medicines.org.uk. Date of
access: 30/12/11.
(4) Neurological disease: Diseases of voluntary muscle. Myasthenia gravis. In: Kumar P, Clark
M, editors. Kumar & Clark Clinical Medicine. Sixth edition. Edinburgh: Elsevier Saunders,
2006: 1268-1269.
(5) Dollery C. Pyridostigmine (bromide). In: Therapeutic Drugs (2nd edition). Churchill
Livingstone. Edinburgh., 1999.
(6) Neostigmine. Latest modification 23/09/2011. Sweetman SC (ed), Martindale: The Complete
Drug Reference. [online] London: Pharmaceutical Press
<http://www.medicinescomplete.com/>. Accessed on 30/12/2011.
(7) Havard CW. Diseases of the central nervous system. Myasthenia gravis. Br Med J 1975;
4:152-154.
(8) Pyridostigmine: Reversal of neuromuscular blockade, Non-depolarizing neuromuscular
blocking agents. Klasco RK (Ed): DRUGDEX® System (electronic version). Thomson
Micromedex, Greenwood Village, Colorado, USA. Available at: http://www.thomsonhc.com
(cited: 30/12/11).
Quality Assurance
Prepared by
Alexandra Denby, London Medicines Information Service (Northwick Park Hospital)
Date Prepared
January 2012
From the NHS Evidence website www.evidence.nhs.uk
2
Medicines Q&As
Checked by
Sheena Vithlani, London Medicines Information Service (Northwick Park Hospital)
Date of check
January 2012
Search strategy




Embase (“(PYRIDOSTIGMINE/ad,do,dt,iv,po,pk) AND (NEOSTIGMINE/cm,do,dt,im,iv,po,pk)
[Limit to: human]”)
Medline (“(NEOSTIGMINE/ad,pk,tu) AND (PYRIDOSTIGMINE BROMIDE/ad,pk,tu) [Limit to:
Humans and English Language] )
In-house database/ resources
Manufacturers (S Yates, Medical Information Officer, Valeant Pharmaceuticals, 06/11/08; A
Slabbert, Medical Information Officer, Hameln pharmaceuticals ltd, 11/11/08)
From the NHS Evidence website www.evidence.nhs.uk
3