From the FDA Drug Label
PRECAUTIONS Pyridostigmine is mainly excreted unchanged by the kidney6,7,8. Therefore, lower doses may be required in patients with renal disease, and treatment should be based on titration of drug dosage to effect6,7.
The FDA drug label does not answer the question.
From the Research
Mestinon (pyridostigmine) can be used as a pro re nata (PRN) or "as needed" medication in certain situations, but its use should be carefully considered due to the potential risks of morbidity and polypharmacy, as highlighted in a study published in 2025 1. When used PRN, Mestinon is typically prescribed for patients with myasthenia gravis who experience occasional worsening of symptoms or breakthrough weakness. The usual PRN dose is 30-60 mg, taken orally when needed, with a maximum of 4-5 doses per day. However, it's essential to note that Mestinon has a relatively short duration of action (3-4 hours), so PRN use alone is often not sufficient for managing myasthenia gravis symptoms. Most patients require regular, scheduled doses throughout the day for optimal symptom control. Some key points to consider when using Mestinon PRN include:
- Patient education on recognizing symptoms and when to take the medication
- Awareness of potential side effects, such as gastrointestinal upset or increased sweating
- Instruction to contact their healthcare provider if symptoms worsen or do not improve with PRN use
- The importance of monitoring and evaluating the effectiveness of PRN medication, as well as its potential impact on regular scheduled medications, as discussed in a study published in 2021 2
- The need for alternative non-pharmacological strategies, such as de-escalation techniques, to reduce the reliance on PRN medication, as suggested in a study published in 2019 3 The effectiveness of Mestinon as a PRN medication is due to its mechanism of action as an acetylcholinesterase inhibitor, which temporarily improves neuromuscular transmission and muscle strength in myasthenia gravis patients. Nevertheless, the use of PRN medication should be guided by the principles of minimizing morbidity, mortality, and optimizing quality of life, and should be based on the most recent and highest-quality evidence available, such as the study published in 2025 1.