Comprehensive medication guide to Amifampridine including estimated pricing, availability information, side effects, and how to find it in stock at your local pharmacy.
Estimated Insurance Pricing
$0/month for eligible commercially insured patients with Catalyst Pathways copay assistance; Medicare Part D patients benefit from the $2,000 annual out-of-pocket cap (2025). Tier 4–5 specialty tier; prior authorization required by all major payers.
Estimated Cash Pricing
$31,000–$34,000 at list price for 120 tablets (specialty drug dispensed through specialty pharmacies only); eligible patients using the Catalyst Pathways program average less than $2/month out of pocket with commercial insurance.
Medfinder Findability Score
45/100
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Amifampridine (brand name Firdapse) is a prescription oral medication and the only FDA-approved treatment for Lambert-Eaton Myasthenic Syndrome (LEMS), a rare autoimmune disorder affecting the neuromuscular junction. Also known as 3,4-diaminopyridine (3,4-DAP), it has been used to treat LEMS since the 1990s — first through compassionate use programs and then through formal FDA approval in November 2018.
LEMS affects approximately 1 in 100,000 people in the United States and is associated with small-cell lung cancer in 50–60% of cases. The condition causes muscle weakness — particularly of the hips, thighs, and shoulders — as well as autonomic symptoms like dry mouth, blurred vision, and changes in sweating.
Amifampridine carries orphan drug designation from the FDA and is dispensed exclusively through specialty pharmacies. It is available as Firdapse (amifampridine phosphate 10 mg tablets), manufactured by Catalyst Pharmaceuticals.
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Amifampridine is a voltage-gated potassium channel blocker. In LEMS, antibodies block voltage-gated calcium channels (VGCCs) on presynaptic nerve terminals, reducing acetylcholine (ACh) release and causing muscle weakness. Amifampridine addresses this by blocking potassium channels in the nerve terminal membrane.
By blocking potassium channels, amifampridine prolongs the duration of the presynaptic action potential. This keeps the remaining functional calcium channels open longer, allowing more calcium to enter the nerve terminal. The increased calcium triggers greater release of ACh-containing vesicles into the synaptic cleft, providing a stronger signal to muscles and reducing weakness.
Amifampridine is a symptomatic treatment — it compensates for the LEMS-related deficit in ACh release but does not eliminate the underlying autoimmune process. It is metabolized primarily by NAT2 in the liver, with a half-life of approximately 1.8–2.5 hours, requiring 3–5 daily doses to maintain effect.
10 mg — tablet
White to off-white round scored tablet. Standard form for adults and pediatric patients 6 years and older.
Amifampridine (Firdapse) is not on the FDA's drug shortage list as of 2026. However, it is one of the most difficult specialty medications to access because it treats an extremely rare condition (LEMS) and is distributed exclusively through specialty pharmacies. You will not find it at any retail pharmacy.
Key access barriers include mandatory prior authorization (required by all major insurers), specialty pharmacy routing, and the loss of the only competing brand (Ruzurgi) in 2022. Patients must work through the Catalyst Pathways program and an in-network specialty pharmacy to obtain the medication. The process typically takes 1–15 days depending on insurance review speed.
If you're having trouble identifying which specialty pharmacy can fill your prescription, medfinder can help — we call pharmacies on your behalf to find which ones can fill your prescription and text you the results.
Amifampridine is not a controlled substance and has no DEA scheduling requirements. However, insurance prior authorization policies effectively require prescriptions to originate from a neurologist or neuromuscular specialist to be approved for coverage. The following specialists are qualified to evaluate LEMS and prescribe amifampridine:
Neurologists (general)
Neuromuscular specialists (strongly preferred for initial diagnosis)
Neurologists at academic medical centers with neuromuscular disease programs
While primary care physicians may have prescribing authority, they are generally not appropriate first prescribers given the diagnostic complexity of LEMS. Telehealth consultation with established LEMS patients is available at some academic medical centers.
No. Amifampridine (Firdapse) is not a controlled substance and is not scheduled by the DEA. There are no DEA-specific prescribing restrictions, no mandatory PDMP reporting requirements, and no legal limits on refills based on controlled substance scheduling. Any licensed prescriber with appropriate clinical expertise may prescribe it.
While access is not restricted by DEA scheduling, insurance companies effectively limit prescribing to neurologists or neuromuscular specialists through prior authorization requirements. Amifampridine does carry an orphan drug designation, and prescriptions must go through approved specialty pharmacies that are in-network with the patient's insurance plan.
The most frequently reported side effects in clinical trials include:
Paresthesia/dysesthesia — tingling or numbness, particularly oral paresthesia (69%)
Elevated liver enzymes (ALT, AST, LDH, GGT) — 14%
Back pain — 14%
Headache — 14%
Muscle spasm — 12%
Dizziness — 10%
Asthenia (fatigue/weakness) — 10%
Serious side effects requiring immediate medical attention:
Seizures — approximately 2% incidence at recommended doses; contraindicated in patients with seizure history
Anaphylaxis/severe allergic reaction — seek emergency care for hives, difficulty breathing, facial swelling
Bronchial hypersecretion or asthma exacerbation in susceptible patients
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Pyridostigmine (Mestinon)
Acetylcholinesterase inhibitor used off-label for LEMS. Works on the postsynaptic side of the neuromuscular junction; generally less effective as monotherapy for LEMS but widely available at retail pharmacies and inexpensive.
IVIG (Intravenous Immunoglobulin)
Pooled antibody IV infusion used for immune modulation in moderate-to-severe LEMS or acute flares. Provides temporary improvement; often used as bridge therapy or combined with other treatments.
Prednisone + Azathioprine
Immunosuppressive combination for sustained immune control in LEMS. Takes weeks to months to show full effect; used for moderate-to-severe or refractory cases.
Plasmapheresis
Mechanical removal of VGCC antibodies from plasma. Provides rapid but short-lived relief; used in LEMS crisis or as bridge therapy.
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Fluoroquinolone antibiotics (ciprofloxacin, levofloxacin)
majorLower the seizure threshold; risk of seizure when combined with amifampridine is significantly increased.
Tricyclic antidepressants (amitriptyline, nortriptyline)
majorLower the seizure threshold; use with caution and neurologist awareness when combined with amifampridine.
Bupropion (Wellbutrin)
majorKnown to lower seizure threshold; increased seizure risk with concurrent amifampridine use.
Antipsychotics (clozapine, olanzapine, chlorpromazine)
majorMay lower seizure threshold; requires careful monitoring when combined with amifampridine.
ADHD stimulants (amphetamines, methylphenidate)
moderateCan lower seizure threshold; discuss with neurologist before combining with amifampridine.
Pyridostigmine (Mestinon)
moderateAdditive cholinergic effects; combination is commonly used therapeutically for LEMS but may increase cholinergic side effects (cramping, secretions).
Tramadol
moderateLowers seizure threshold; increased seizure risk when combined with amifampridine.
Compounded amifampridine (3,4-DAP)
majorTaking both Firdapse and compounded amifampridine is essentially double-dosing and dramatically increases seizure risk. Do not combine.
Amifampridine (Firdapse) represents a meaningful advance for LEMS patients — it's the first and only FDA-approved oral therapy for a condition that, until 2018, had no formally approved treatment. For most patients, it significantly reduces muscle weakness and improves daily function. The most important side effect to know is the seizure risk (~2% at recommended doses), which is why a seizure history is an absolute contraindication.
Access is the primary challenge. The drug's $375,000+ annual list price is alarming, but the Catalyst Pathways program dramatically reduces out-of-pocket costs for eligible commercially insured patients to near zero. Medicare patients benefit from the 2025 $2,000 annual out-of-pocket cap. The real barriers are prior authorization timelines, specialty pharmacy routing, and the 2022 withdrawal of the only competing product (Ruzurgi).
If you're struggling to find a pharmacy that can fill your amifampridine prescription, medfinder calls pharmacies on your behalf and texts you which ones can fill it — saving you hours of frustrating phone calls.
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Our medication guides are researched and written to help patients make informed decisions. All content is reviewed for accuracy and updated regularly. Learn more about our standards
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Medfinder is actively checking pharmacy inventory for Amifampridine. We don't publish a number until we have enough verified pharmacy checks to be accurate — start a search and our team confirms current availability near you, usually within 24 hours.
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