Firdapse

Last updated on RxList: 3/11/2021
Firdapse Side Effects Center

Medical Editor: John P. Cunha, DO, FACOEP

What Is Firdapse?

Firdapse (amifampridine) is a potassium channel blocker indicated for the treatment of Lambert-Eaton myasthenic syndrome (LEMS) in adults.

What Are Side Effects of Firdapse?

Common side effects of Firdapse include:

Dosage for Firdapse

The recommended starting dosage of Firdapse is 15 mg to 30 mg daily taken orally in divided doses (3 to 4 times daily). Starting dosage is 15 mg daily for patients with renal impairment, hepatic impairment, and in known N-acetyltransferase 2 (NAT2) poor metabolizers. Dosage can be increased by 5 mg daily every 3 to 4 days.

What Drugs, Substances, or Supplements Interact with Firdapse?

Firdapse may interact with drugs that lower seizure threshold and drugs with cholinergic effects (e.g., direct or indirect cholinesterase inhibitors). Tell your doctor all medications and supplements you use.

Firdapse During Pregnancy and Breastfeeding

Tell your doctor if you are pregnant or plan to become pregnant before using Firdapse; it may harm a fetus. It is unknown if Firdapse passes into breast milk. Consult your doctor before breastfeeding.

Additional Information

Our Firdapse (amifampridine) Tablets, for Oral Use Side Effects Drug Center provides a comprehensive view of available drug information on the potential side effects when taking this medication.

This is not a complete list of side effects and others may occur. Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.

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Firdapse Consumer Information

Get emergency medical help if you have signs of an allergic reaction: hives; difficult breathing; swelling of your face, lips, tongue, or throat.

Amifampridine can cause seizures, even if you have never had a seizure in the past.

Stop using amifampridine and call your doctor at once if you have a seizure.

Common side effects may include:

  • tingly feeling in your hands, feet, face, mouth, or other parts of your body;
  • nausea, stomach pain, diarrhea;
  • headache, back pain;
  • increased blood pressure;
  • abnormal liver function tests;
  • muscle spasms; or
  • cold symptoms such as stuffy nose, sneezing, sore throat.

This is not a complete list of side effects and others may occur. Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.

Read the entire detailed patient monograph for Firdapse (Amifampridine Tablets)

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Firdapse Professional Information

SIDE EFFECTS

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

  • Seizures [see WARNINGS AND PRECAUTIONS]
  • Hypersensitivity [see WARNINGS AND PRECAUTIONS]

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.

DRUG INTERACTIONS

Drugs That Lower Seizure Threshold

The concomitant use of FIRDAPSE and drugs that lower seizure threshold may lead to an increased risk of seizures [see WARNINGS AND PRECAUTIONS]. The decision to administer FIRDAPSE concomitantly with drugs that lower the seizure threshold should be carefully considered in light of the severity of the associated risks.

Drugs With Cholinergic Effects

The concomitant use of FIRDAPSE and drugs with cholinergic effects (e.g., direct or indirect cholinesterase inhibitors) may increase the cholinergic effects of FIRDAPSE and of those drugs and increase the risk of adverse reactions.

Read the entire FDA prescribing information for Firdapse (Amifampridine Tablets)

© Firdapse Patient Information is supplied by Cerner Multum, Inc. and Firdapse Consumer information is supplied by First Databank, Inc., used under license and subject to their respective copyrights.

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