Firdapse

Firdapse is a prescription medication used to treat adults with Lambert-Eaton myasthenic syndrome (LEMS), a severe neuromuscular disorder that causes debilitating, progressive muscle weakness and fatigue. LEMS occurs when the immune system attacks the connections between nerves and muscles, known as the neuromuscular junction (NMJ).

Firdapse belongs to a group of drugs called potassium channel blockers. In LEMS, antibodies block the calcium channel in nerve cells, reducing the amount of ACh released into the NMJ. Firdapse works by blocking the potassium channel in the nerve cell, which keeps calcium channels open longer, allowing more ACh to be released into the NMJ.

This medication comes in tablet form. It is taken up to 4 times daily, with or without food.

Common side effects include tingling around the mouth, tongue, face, fingers, toes, and other body parts. Firdapse can also cause dizziness. Do not drive or operate heavy machinery until you know how Firdapse affects you.

Firdapse is a prescription medication used to treat Lambert-Eaton myasthenic syndrome (LEMS) in adults. LEMS is a condition where the immune system attacks its own body’s tissues where the nerve and muscle tissue meet. This leads to the muscles becoming weak and unable to contract.

This medication may be prescribed for other uses. Ask your doctor or pharmacist for more information.

Serious side effects have been reported with Firdapse. See the “Firdapse Precautions” section.

Common side effects of Firdapse include the following:

• Tingling sensation in the hands, feet, and mouth
• Upper respiratory tract infection
• Stomach pain
• Nausea
• Diarrhea
• Headache
• Back pain
• High blood pressure
• Muscle spasms
• Muscle weakness
• Pain in hands or feet

This is not a complete list of Firdapse side effects. Ask your doctor or pharmacist for more information.

Tell your doctor if you have any side effects that bother you or that do not go away. Call your doctor for medical advice about side effects. You may report side effects to the FDA at 1-800-FDA-1088.

Tell your doctor about all the medicines you take, including prescription and non-prescription medicines, vitamins, and herbal supplements. Especially tell your doctor if you take:

• Medications that can increase the chances of seizures like antidepressants (bupropion (Wellbutrin), sertraline (Zoloft), fluoxetine (Prozac), and others), stimulants (amphetamine and dextroamphetamine (Adderall), methylphenidate (Ritalin), and others), and others.   

• Medications with cholinergic effects like donepezil (Aricept), galantamine (Razadyne), rivastigmine (Exelon), and others.

This is not a complete list of Firdapse drug interactions. Ask your doctor or pharmacist for more information.

Serious side effects have been reported with Firdapse including the following:

• Seizures. Firdapse increases the chances of seizures in people with or without history of seizures. Talk to your healthcare provider if you have history of seizures or if you experience seizure while using Firdapse.

• 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

Firdapse can cause dizziness. Do not drive or operate heavy machinery until you know how Firdapse affects you.

Do not take Firdapse if you:

• Are allergic to Firdapse or to any of its ingredients

• Have ever had a seizure

Medications can interact with certain foods. In some cases, this may be harmful and your doctor may advise you to avoid certain foods. In the case of Firdapse, there are no specific foods that you must exclude from your diet when receiving this medication.

Before taking Firdapse, tell your doctor about all of your medical conditions. Especially tell your doctor if you:

• Are allergic to Firdapse or to any of its ingredients
• Have a history of seizures
• Have liver problems
• Have kidney problems
• Are pregnant or plan to become pregnant
• Are breastfeeding or plan to breastfeed

Tell your doctor about all the medicines you take including prescription and non-prescription medicines, vitamins, and herbal supplements.

Tell your doctor if you are pregnant or plan to become pregnant.

There are no well-controlled studies that have been done in pregnant women. In animal studies, pregnant animals were given this medication and had some babies born with problems. It is not known if Firdapse will harm your unborn baby. You and your doctor will decide if you should take Firdapse while you are pregnant.

Tell your doctor if you are breastfeeding or plan to breastfeed.

It is not known if Firdapse crosses into human milk. Because many medications can cross into human milk and because of the possibility for serious adverse reactions in nursing infants with use of this medication, a choice should be made whether to stop nursing or stop the use of this medication. Talk to your doctor about the best way to feed your baby while taking Firdapse.

• Take Firdapse exactly as your doctor tells you to take it. Do not change your dose of Firdapse.
• Do not take more than 2 tablets of Firdapse at one time or more than 8 tablets in a 24-hour period.
• Firdapse can be taken with or without food.
• If you miss a dose of Firdapse, skip that dose and take your next dose at your next scheduled dose time. Do not double your dose to make up the missed dose.
• Do not take Firdapse together with other medicines known to increase the risk of seizures.
• If you take too much Firdapse, call your doctor or go to the nearest hospital emergency room right away.

Take this medication exactly as prescribed by your doctor. Follow the directions on your prescription label carefully.

The dose your doctor recommends may be based on the following:

• The condition being treated

• Other medical conditions you have

• Other medications you are taking

• How you respond to this medication

The recommended starting dose range of Firdapse (amifampridine) for the treatment of  Lambert-Eaton myasthenic syndrome (LEMS) in adults is 15 mg to 30 mg daily. The dose may be increased by your healthcare provider every 3 or 4 days. The maximum total daily dose is 80 mg.

If you take too much Firdapse, call your healthcare provider or local Poison Control Center, or seek emergency medical attention right away.

• Store Firdapse at room temperature between 68°F to 77°F (20°C to 25°C).

• Keep this and all medicines out of the reach of children.