What is the conversion dose from Mestinon (pyridostigmine) intravenous (IV) to oral (PO)?

Mestinon (Pyridostigmine) IV to PO Conversion

When converting from intravenous (IV) pyridostigmine to oral (PO) pyridostigmine, use a ratio of 1:30, meaning 1 mg IV pyridostigmine equals 30 mg oral pyridostigmine.

Conversion Ratio and Dosing

• The standard conversion ratio for pyridostigmine from IV to PO is 1:30 (1 mg IV equals 30 mg PO) 1
• For example, if a patient is receiving 1 mg IV pyridostigmine, this would be equivalent to 30 mg oral pyridostigmine 1
• When administering intravenously, 30 mg oral pyridostigmine corresponds to 1 mg IV pyridostigmine 1

Pharmacokinetic Considerations

• Oral bioavailability of pyridostigmine is approximately 7.6-14.3%, which explains the need for higher oral dosing 2, 3
• The plasma elimination half-life differs between administration routes:
  • IV administration: approximately 1.5 hours 2
  • Oral administration: approximately 1.8 hours 2
• After oral administration, peak plasma concentrations are typically reached within 1.7-3.2 hours (longer when taken with food) 2

Clinical Applications

Myasthenia Gravis Management

• For myasthenia gravis patients, pyridostigmine dosing typically starts at 30 mg PO three times daily and can be gradually increased to a maximum of 120 mg PO four times daily based on symptoms 1
• When switching between routes, careful monitoring is essential as patients may show variable responses to the same dose 4
• Despite widely different oral doses (60 to 660 mg/day), plasma concentrations are maintained within a relatively narrow range (usually between 20 and 60 ng/ml) 4

Special Considerations

• In patients with myasthenia gravis undergoing surgery, continuing pyridostigmine affects the response to neuromuscular blocking agents 5
• Patients who vomit within 2 hours of taking oral pyridostigmine should repeat the dose or receive IV pyridostigmine 1
• Avoid medications that can worsen myasthenia symptoms when managing these patients, including beta-blockers, IV magnesium, fluoroquinolones, aminoglycosides, and macrolide antibiotics 1

Monitoring After Conversion

• After conversion from IV to PO, monitor for:
  • Adequate symptom control (particularly in myasthenia gravis patients) 1
  • Potential cholinergic side effects including increased salivation, lacrimation, diarrhea, urinary urgency, sweating, and bradycardia 1
  • Need for dose adjustments based on clinical response 1

Remember that individual patient factors may affect the pharmacokinetics of pyridostigmine, and some patients may require dosage adjustments based on their clinical response 4, 2.