FDA approves Lupin's generic amifampridine for LEMS

The FDA has approved Lupin's abbreviated new drug application (ANDA) for amifampridine 10-mg tablets, a generic version of Firdapse (Catalyst Pharmaceuticals) for Lambert-Eaton myasthenic syndrome (LEMS), the company announced November 2, 2026.¹ The product was found bioequivalent to the reference listed drug, and as one of the first ANDA applicants, Lupin is eligible for 180 days of shared generic exclusivity.¹

For clinicians caring for the small number of children with LEMS, the approval is unlikely to change prescribing soon. Under an August 2025 patent settlement, Lupin agreed not to market its generic in the US any earlier than February 25, 2035, unless certain limited circumstances customary in such agreements occur.³

Amifampridine indication and pediatric dosing in LEMS

Brand amifampridine is indicated for LEMS in adults and pediatric patients aged 6 years and older.² Pediatric approval rested on adequate and well-controlled studies in adults, adult pharmacokinetic (PK) data, PK modeling to identify a pediatric regimen, and safety data from patients aged 6 years and older, rather than a dedicated pediatric efficacy trial.² Safety and effectiveness have not been established in children younger than 6 years.²

Dosing in children is weight-based. Patients weighing less than 45 kg start at 5 to 15 mg daily in 3 to 4 divided doses, titrating by 2.5 mg every 3 to 4 days to a maximum single dose of 10 mg and 40 mg per day; those weighing 45 kg or more follow the adult schedule, with a maximum single dose of 20 mg and 80 mg per day.² The scored tablet can be made into a 1-mg/mL suspension for patients who need smaller dose increments, have trouble swallowing, or use a feeding tube.²

Amifampridine efficacy and safety data in LEMS

Efficacy was demonstrated in 2 randomized, double-blind, placebo-controlled withdrawal studies enrolling 64 adults aged 21 to 88 years, with co-primary end points of change in Quantitative Myasthenia Gravis (QMG) and Subject Global Impression (SGI) scores.² In study 2 (n = 26), patients switched to placebo for 4 days had greater worsening in QMG score than those who continued treatment (least squares mean difference, −6.54; 95% CI, −9.78 to −3.29; P = .0004), with a similar pattern for SGI (P = .0003).² Study 1 showed a smaller QMG difference after 14 days (−1.7; 95% CI, −3.4 to −0.0; P = .045).²

Amifampridine is contraindicated in patients with a history of seizures, and seizures occurred in approximately 2% of patients without such a history at recommended doses.² Paresthesia (62%) and upper respiratory tract infection (33%) were the most common adverse reactions in newly treated adults.² In an expanded access program in which 21 children received the drug for at least 1 year, adverse reactions resembled those in adults, except for clinically significant weight loss in 2 patients receiving 60 mg/day or more.² Known N-acetyltransferase 2 (NAT2) poor metabolizers, who can have 5.6- to 9-fold higher exposure, should start at the lowest recommended dose.²

LEMS epidemiology and rarity in children

LEMS is an autoimmune disorder of the neuromuscular junction marked by antibodies against presynaptic voltage-gated calcium channels, and it can be autoimmune or paraneoplastic.⁴ A 2025 nationwide Turkish analysis estimated prevalence at 1.11 per million, with a median age at diagnosis of 60 years (range, 16-88 years); the authors cited a Dutch study reporting a prevalence of 2.3 per million.⁴ That rarity helps explain the reliance on adult data.

Firdapse patent litigation and generic amifampridine timeline

Lupin was among 3 manufacturers that notified Catalyst in January 2023 of ANDAs challenging the 6 Orange Book–listed Firdapse patents, which expire between 2032 and 2037.³ No ANDA could receive final approval until the drug's orphan exclusivity expired on November 26, 2025.³

Limitations and next steps for generic amifampridine

The approval confirms bioequivalence but does not change the evidence base, which comes from short withdrawal periods of 4 and 14 days in adults and limited pediatric safety data.² Settlement terms are confidential and include exceptions that could shift timing.³ Lupin's announcement did not address launch plans or pricing.¹

References

1. Lupin Limited. Lupin receives U.S. FDA approval for amifampridine tablets. News release. November 2, 2026. Accessed November 3, 2026. https://www.lupin.com/media/press-releases/lupin-receives-u-s-fda-approval-for-amifampridine-tablets

2. Firdapse (amifampridine) tablets. Prescribing information. Catalyst Pharmaceuticals Inc; 2022. Accessed November 3, 2026. https://www.accessdata.fda.gov/drugsatfda_docs/label/2022/208078s008lbledt.pdf

3. Catalyst Pharmaceuticals Inc. Form 10-Q for the quarterly period ended September 30, 2025. US Securities and Exchange Commission. Accessed November 3, 2026. https://www.sec.gov/Archives/edgar/data/1369568/000119312525266854/cprx-20250930.htm

4. Inan B, Ozturk B, Ata N, et al. Epidemiological analysis of Lambert-Eaton myasthenic syndrome in Türkiye: insights from a nationwide electronic health database. Front Neurol. 2025;16:1667540. doi:10.3389/fneur.2025.1667540