Firdapse (amifampridine)

Firdapse (amifampridine)

Generic drug: amifampridine

Brand name: Firdapse

What is Firdapse (amifampridine), and how does it work?

Firdapse is a prescription medicine used to treat Lambert-Eaton myasthenic syndrome (LEMS), an autoimmune disease, in adults.

It is not known if Firdapse is safe or effective in children.

What are the side effects of Firdapse?

Firdapse may cause serious side effects, including:

  • Seizures.
  • Serious allergic reactions, such as anaphylaxis. Firdapse can cause serious allergic reactions. Stop taking Firdapse and call your doctor right away or get emergency medical help if you have:

The most common side effects of Firdapse include:

Tell your doctor if you have any side effect that bothers you or that does not go away.

These are not all the possible side effects of Firdapse.

Call your doctor for medical advice about side effects. You may report side effects to FDAat 1-800-FDA-1088.

What is the 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).
  • The dosage canbe increased by 5 mg daily every 3 or 4days.
  • The maximum recommended total daily dosage is 80 mg.
  • The maximum single dose is 20 mg.
  • If a dose is missed, patients should not take double or extra doses.

Patients With Renal Impairment

  • The recommended starting dosage of Firdapse in patients with renal impairment (creatinine clearance 15 to 90 mL/min) is 15 mg daily, taken orally in 3 divided doses. No dosage recommendation for Firdapse can be made for patients with end-stage renal disease.

Patients With Hepatic Impairment

  • The recommended starting dosage of Firdapse in patients with any degree of hepatic impairment is 15 mg daily, taken orally in 3 divided doses.

Known N-acetyltransferase 2 (NAT2) Poor Metabolizers

  • The recommended starting dosage of Firdapse in known N-acetyltransferase 2 (NAT2) poor metabolizers is 15 mg daily, taken orally in 3 divided doses.

Administration Instructions

  • Firdapse can be taken without regard to food.

What drugs interact with Firdapse?

Drugs That Lower Seizure Threshold

The concomitant use of Firdapse and drugs that lower seizure threshold may lead to an increased risk of seizures. 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.

Is Firdapse safe to use while pregnant or breastfeeding?

  • There are no data on the developmental risk associated with the use of Firdapse in pregnant women.
  • There is a pregnancy exposure registry that monitors pregnancy outcomes in women exposed to Firdapse during pregnancy. Physicians are encouraged to enroll pregnant patients, or pregnant women may register themselves in the registry by calling 855-212-5856 (toll-free), using the Fax number 877-867-1874 (toll-free), by contacting the Pregnancy Coordinating Center at [email protected], or by visiting the study website
  • There are no data on the presence of Firdapse in human milk, the effects on the breastfed infant, or the effects on milk production.
  • The developmental and health benefits of breastfeeding should be considered along with the mother’s clinical need for Firdapse and any potential adverse effects on the breastfed infant from Firdapse or from the underlying maternal condition.


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Medically Reviewed on 3/31/2021


All sections courtesy of the U.S. Food and Drug Administration