Onset of Muscle Twitching After Oral Neostigmine
The evidence provided does not address oral neostigmine administration or its timeline for muscle twitching onset, as all guidelines and studies focus exclusively on intravenous (IV) neostigmine used in anesthesia settings for neuromuscular blockade reversal.
Critical Context Gap
The available evidence presents a fundamental mismatch with your question:
- All dosing, timing, and effect data pertain to IV neostigmine at doses of 40-80 mcg/kg (approximately 2.8-5.6 mg for a 70 kg person), administered during anesthesia to reverse paralytic agents 1, 2
- Your scenario involves 45 mg oral neostigmine, which is 8-16 times higher than typical IV doses and uses a completely different route of administration
- Oral neostigmine is typically used for myasthenia gravis, not neuromuscular blockade reversal, and has different pharmacokinetics than IV administration 3
What We Know About IV Neostigmine Timing (Not Directly Applicable)
For IV administration in the anesthesia context:
- Peak neuromuscular effects occur at 5-10 minutes after IV injection 4, 5
- Neostigmine increases muscle action potential amplitude and diminishes weakness within 2 minutes of IV administration 4
- Maximum pharmacological effect is typically reached between 7-15 minutes after IV dosing 4
- Time to peak effect ranges from 6-10 minutes depending on the specific muscle relaxant being reversed 5, 6
Why This Cannot Answer Your Question
Oral bioavailability and absorption kinetics are fundamentally different from IV administration:
- IV neostigmine has immediate systemic availability, while oral neostigmine must undergo gastrointestinal absorption
- The 45 mg oral dose suggests a myasthenia gravis indication (typical oral doses are 15-375 mg/day divided), where the therapeutic goal is improved muscle strength, not the "twitching" seen with excessive cholinergic stimulation
- Muscle twitching (fasciculations) from neostigmine typically indicates cholinergic excess or paradoxical weakness, not therapeutic effect 7
Clinical Concern
If you are experiencing or anticipating muscle twitching from 45 mg oral neostigmine, this may represent:
- Cholinergic crisis (excessive acetylcholine), which is a medical emergency
- The dose of 45 mg orally is substantial and timing of adverse effects would depend on absorption, which typically peaks 1-2 hours after oral administration for most medications
This question requires consultation with the prescribing physician or poison control if concerning symptoms are occurring.