Firdapse

Firdapse is a a potassium channel blocker used to treat Lambert-Eaton myasthenic syndrome (LEMS), an autoimmune disease, in adults and children 6 years of age and older.

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:
  • shortness of breath or trouble breathing
  • swelling of your throat or tongue
  • hives

The most common side effects of Firdapse include:

• tingling around the mouth, tongue, face, fingers, toes, and other body parts
• upper respiratory infection
• stomach pain
• nausea
• diarrhea
• headache
• increased liver enzymes
• back pain
• high blood pressure
• muscle spasms

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.

The recommended dosage regimen of Firdapse for adults and pediatric patients 6 years of age and older is included in Table 1. For pediatric patients, the recommended dosing regimen is dependent on body weight. Dosage should be increased every 3 to 4 days based on clinical response and tolerability. Titration increments should not exceed those shown in Table 1.

Table 1: Recommended Oral Dosage for the Treatment of LEMS in Adults and Pediatric Patients 6 Years of Age and Older

Missed Dose

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 (CLcr) 15 to 90 mL/min] is the lowest recommended initial daily dosage (i.e., 15 mg daily for pediatric patients weighing 45 kg or more and for adults, and 5 mg daily for pediatric patients weighing less than 45 kg) taken orally in 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 the lowest recommended initial daily dosage (i.e., 15 mg daily for pediatric patients weighing 45 kg or more and for adults, and 5 mg daily for pediatric patients weighting less than 45 kg) taken orally in divided doses.

Known N-acetyltransferase 2 (NAT2) Poor Metabolizers

The recommended starting dosage of Firdapse in known N-acetyltransferase 2 (NAT2) poor metabolizers is the lowest recommended initial daily dosage (i.e., 15 mg daily for pediatric patients weighing 45 kg or more and for adults, and 5 mg daily for pediatric patients weighing less than 45 kg) taken orally in divided doses.

Administration Instructions

Firdapse can be taken without regard to food.

Preparation of a 1mg/mL Suspension (see the Instructions for Use for full instructions on how to prepare the 1mg/mL suspension)

When patients require a dosage in less than 5 mg increments, have difficulty swallowing tablets, or require feeding tubes, a 1 mg/mL suspension can be prepared (e.g., by placing the required number of tablets in a 50 to 100 mL container, adding 10 mL of sterile water for each tablet, waiting for 5 minutes, and shaking well for 30 seconds).

Crushing the tablets prior to making the suspension is not necessary. After preparation of the suspension, an oral syringe can be used to draw up and administer the correct dose by mouth or by feeding tube.

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.

• There are no data on the developmental risk associated with the use of Firdapse in pregnant individuals.
• There is a pregnancy exposure registry that monitors pregnancy outcomes when exposed to Firdapse during pregnancy. Physicians are encouraged to enroll pregnant patients, or you may register 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 www.firdapsepregnancystudy.com
• 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 your clinical need for Firdapse and any potential adverse effects on the breastfed infant from Firdapse or from the underlying maternal condition.