Section 07 · Monograph
Amifampridine
Reviewed Nov 2026FDA label
FirdapseK+ channel blocker
- Forms
- Tab: 10mg
- Dose
- LEMS: start 15-30mg/day in 3-4 doses, increase 5mg every 3-4 days; max single dose 20mg, max 80mg/day
- MOA
- Blocks presynaptic K+ channels, ↑ACh release
Indications
- Lambert-Eaton myasthenic syndrome (LEMS) in adults and pediatric patients 6 years of age and olderFDA-labeled
Mechanism of Action
- Voltage-gated potassium channel blocker that prolongs presynaptic depolarization, increasing calcium entry and acetylcholine release at the neuromuscular junction
Full Dosing
Adult / usual
- Adults: start 15-30mg/day in 3-4 divided doses; increase by 5mg/day every 3-4 days; maximum single dose 20mg; maximum 80mg/day
- 10mg tablets are functionally scored; a 1mg/mL suspension may be prepared for small increments or feeding tubes
Renal
- Lower starting dose in renal or hepatic impairment and in known NAT2 poor metabolizers
Pediatric
- Pediatric: weight-based — 45kg or more start 15mg/day (maximum 100mg/day); under 45kg start 5mg/day (maximum 50mg/day), increasing by 2.5mg/day
Contraindications
- History of seizures
- Known hypersensitivity to amifampridine
Drug Interactions
- Drugs that lower seizure threshold
- QT-prolonging drugs
- Other acetylcholinesterase inhibitors may increase cholinergic effects
Adverse Effects
- Perioral and distal paresthesias
- Abdominal pain, nausea, diarrhea
- Seizures (dose-related)
- Hypertension, elevated liver enzymes
- Cataract, dizziness, muscle spasms
Monitoring Parameters
- Seizure activity
- Blood pressure and liver enzymes
- Renal and hepatic function; NAT2 status if known
Pregnancy & Lactation
- Limited human data; animal studies did not show embryofetal harm at lower exposures — use if benefit justifies risk
- Unknown whether present in milk