• Generic Name: amifampridine tablets
  • Brand Name: Firdapse
  • Drug Class: Potassium Channel Blockers, Cholinergic Agonists
Last updated on MDtodate: 10/5/2022


The following serious adverse reactions are described elsewhere in the labeling:

  • Seizures
  • Hypersensitivity

Clinical TrialsExperience

Because clinical trials are conducted under widely varying conditions, adverse reaction rates observed in the clinical trials of a drug cannot be directly compared to rates in the clinical trials of another drug and may not reflect the rates observed in practice.

In controlled and uncontrolled trials (Study 1 and 2) in patients with LEMS, 63 patients were treated with FIRDAPSE, including 40 patients treated for more than 6 months, and 39 patients treated for more than 12 months. In an expanded access program, 139 patients with LEMS were treated with FIRDAPSE, including 102 patients treated for more than 6 months, 77 patients treated for more than 12 months, and 53 patients treated for more than 18 months.

Study 1 was a double-blind, placebo-controlled, randomized discontinuation study in adults with LEMS. Following an initial open-label run-in phase (up to 90 days), patients were randomized to either continue FIRDAPSE treatment or transition to placebo, for a 14-day double-blind phase. Following final assessments, patients were allowed to resume FIRDAPSE treatment for up to 2 years (open-label long-term safety phase of the study).

During the open-label run-in phase of Study 1, 53 patients received FIRDAPSE for an average of 81 days at a mean daily dosage of 50.5 mg/day. The mean patient age was 52.1 years and 66% were female. There were 42 patients who had no prior exposure to FIRDAPSE at the initiation of this study. Table 1 shows adverse reactions with an incidence of 5% or greater occurring in the 42 LEMS patients newly initiated on treatment with FIRDAPSE during the run-in phase of the study.

Table 1: Adverse Reactions in ≥5% of LEMS Patients Newly Treated with FIRDAPSE in Study 1

Adverse Reaction FIRDAPSE
N=42 %
Paresthesia* 62
Upper respiratory tract infection 33
Abdominal pain 14
Nausea 14
Diarrhea 14
Headache 14
Elevated liver enzymes** 14
Back pain 14
Hypertension 12
Muscle spasms 12
Dizziness 10
Asthenia 10
Muscular weakness 10
Pain in extremity 10
Cataract 10
Constipation 7
Bronchitis 7
Fall 7
Lymphadenopathy 7
*Includes paresthesia, oral paresthesia, oral hypoesthesia
**Includes elevated alanine aminotransferase (ALT), aspartate aminotransferase (AST), lactate dehydrogenase (LDH), and gamma-glutamyl transferase (GGT)


Other Adverse Reactions

In the overall population treated in Study 1 (n=53), including the double-blind phase and the 2-year open-label long-term safety phase, additional adverse reactions occurring in at least 5% of the patients included: dyspnea, urinary tract infection, gastroesophageal reflux, insomnia, peripheral edema, pyrexia, viral infection, blood creatine phosphokinase increase, depression, erythema, hypercholesterolemia, and influenza. These patients received a mean daily dosage of 66 mg of FIRDAPSE.