What Is Amifampridine (Firdapse)? Uses, Dosage, and What You Need to Know in 2026

Amifampridine — sold under the brand name Firdapse — is a prescription medication and the only FDA-approved oral treatment for Lambert-Eaton Myasthenic Syndrome (LEMS), a rare and serious autoimmune disease that affects the neuromuscular junction. Here's everything you need to know about this medication.

What Is Amifampridine?

Amifampridine (generic name) is also known as 3,4-diaminopyridine (3,4-DAP). It is a voltage-gated potassium channel blocker classified as a cholinergic muscle stimulant. The FDA-approved brand is Firdapse, manufactured by Catalyst Pharmaceuticals of Coral Gables, Florida.

Amifampridine has been used to treat LEMS since the 1990s — initially through compassionate use programs before FDA formal approval. The phosphate salt form (amifampridine phosphate) was approved by the FDA in November 2018 for adults and expanded to pediatric patients 6 years and older in October 2022.

What Is LEMS and Who Does It Affect?

Lambert-Eaton Myasthenic Syndrome (LEMS) is a rare autoimmune disorder affecting approximately 1 in 100,000 people in the United States. In LEMS, the immune system produces antibodies that attack voltage-gated calcium channels (VGCCs) on presynaptic nerve terminals at the neuromuscular junction. This attack reduces the release of acetylcholine (ACh), the chemical messenger that carries nerve signals to muscles, resulting in muscle weakness — typically in the hips, thighs, shoulders, and arms.

LEMS is associated with cancer — particularly small-cell lung cancer (SCLC) — in approximately 50–60% of cases. In these patients, LEMS is considered paraneoplastic: the immune system's attack on cancer cells cross-reacts with VGCCs in nerve terminals. In the remaining 40–50% of cases, LEMS is a primary autoimmune disorder without underlying malignancy.

What Is Amifampridine Approved For?

Amifampridine (Firdapse) has one FDA-approved indication:

Lambert-Eaton Myasthenic Syndrome (LEMS) in adults and pediatric patients 6 years of age and older

The drug has also been studied historically for congenital myasthenic syndromes and was investigated for multiple sclerosis, though a 2002 Cochrane review found no unbiased evidence to support MS use. The FDA-approved indication remains limited to LEMS.

Amifampridine Dosage: How Much and How Often?

Amifampridine (Firdapse) comes as 10 mg oral tablets. It is taken 3–5 times per day, as the drug has a short half-life of approximately 1.8–2.5 hours and must be taken frequently to maintain its effect.

For adults (age 17+):

Starting dose: 15–30 mg per day in 3–4 divided doses

Maximum single dose: 20 mg

Maximum daily dose: 100 mg (updated by FDA in May 2024, previously 80 mg)

For pediatric patients (ages 6–17):

Children weighing less than 45 kg: maximum 50 mg/day; max single dose 15 mg

Children weighing 45 kg or more: maximum 100 mg/day; max single dose 30 mg

Doses are gradually increased (titrated up by 5 mg/day every 3–4 days for adults) based on clinical response and tolerability. Your neurologist will determine the right dose for you. The drug can be taken with or without food.

39,483+ patients found their medications in stock

39K+

Find Amifampridine In Stock Today →

Special Populations: Renal Impairment

Patients with renal impairment (CrCl 15–90 mL/min) should start at a lower dose of 15 mg/day in 3 divided doses, with close monitoring. Amifampridine has not been studied in patients with end-stage renal disease (CrCl <15 mL/min or on dialysis), so no dose recommendation exists for that group.

Is Amifampridine a Controlled Substance?

No. Amifampridine (Firdapse) is not a controlled substance and is not scheduled by the DEA. There are no special DEA prescribing restrictions, no mandatory prescription drug monitoring program (PDMP) reporting requirements, and no restrictions on refills based on controlled substance laws. The access challenges come from insurance requirements, not legal scheduling.

Skip the calls, skip the stress.

Find Amifampridine In Stock Today →

50K+

Medications
Found

99%

Success
Rate

6+

Hours saved
on average

Who Makes Amifampridine?

Firdapse is manufactured by Catalyst Pharmaceuticals, Inc., based in Coral Gables, Florida. Catalyst licensed the US rights from BioMarin Pharmaceutical in 2012 and received FDA approval in November 2018. The drug has orphan drug designation in both the US and EU, reflecting the rarity of the condition it treats.

Learn more: How Does Amifampridine Work? Mechanism of Action Explained and Amifampridine Side Effects: What to Expect.