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Overview: Firdapse is used to treat Lambert-Eaton myasthenic syndrome. Firdapse is thought to work by blocking potassium channels, which allows more calcium to enter nerve cells and release acetylcholine, a chemical that helps improve muscle movement. Common side effects include stomach or back pain, nausea, diarrhea, headache, and muscle spasms. Firdapse is available as a tablet that is swallowed.

Uses

What is Firdapse used for?

Firdapse (amifampridine) is used to treat Lambert-Eaton myasthenic syndrome (LEMS). LEMS is a rare autoimmune disease that affects some people who have small-cell lung cancer as well as some people who do not have cancer. It happens when the immune system mistakenly attacks the place where your nerves and muscles connect. LEMS causes damage to nerve endings, which leads to symptoms of weakness, tingling, and in some cases, other symptoms. 

Firdapse may also be used for other conditions as determined by your health care provider.

How does Firdapse work (mechanism of action)?

The exact way Firdapse works is not fully understood. It is thought to work by blocking potassium channels, which allows more calcium to enter nerve cells and release acetylcholine, a chemical that helps improve muscle movement.

How is Firdapse supplied (dosage forms)?

Brands and other names

  • Firdapse
  • Ruzurgi

Dosage forms and strengths

  • 10 mg oral tablets

How should I store Firdapse?

Firdapse should be stored at room temperature, between 68 F and 77 F (20 C and 25 C). It can be exposed to temperatures between 59 F and 86 F (15 C and 30 C) for shorter periods of time, such as when transporting it. Store in a cool, dry place.

If you prepare the suspension, you should only prepare enough for one day at a time. Store it in the refrigerator between 36 F and 46 F (2 C and 8 C) between doses. The suspension can be stored for up to 24 hours. Throw away any unused suspension after 24 hours.

Side Effects

What are the most common side effects of Firdapse?

The most common side effects of Firdapse are listed below. Tell your health care provider if you have any of these side effects that bother you.

  • Numbness, tingling, or burning in your arms, feet, or face
  • Changes in liver function tests
  • Infection in the nose or throat, sore throat, or common cold symptoms
  • High blood pressure
  • Stomach pain
  • Back pain
  • Nausea
  • Diarrhea
  • Headache
  • Muscle spasms

There may be other side effects of Firdapse that are not listed here. Contact your health care provider if you think you are having a side effect of a medicine. In the U.S., you can report side effects to the FDA at www.fda.gov/medwatch or by calling 800-FDA-1088 (800-332-1088). In Canada, you can report side effects to Health Canada at www.health.gc.ca/medeffect or by calling 866-234-2345.

What are the serious side effects of Firdapse?

While less common, the most serious side effects of Firdapse are described below, along with what to do if they happen.

Severe Allergic Reactions. Firdapse may cause allergic reactions, which can be serious. Stop taking Firdapse and get help right away if you have any of the following symptoms of a serious allergic reaction.

  • Breathing problems or wheezing
  • Racing heart
  • Fever or general ill feeling
  • Swollen lymph nodes
  • Swelling of the face, lips, mouth, tongue, or throat
  • Trouble swallowing or throat tightness
  • Itching, skin rash, or pale red bumps on the skin called hives
  • Nausea or vomiting
  • Dizziness, feeling lightheaded, or fainting
  • Stomach cramps
  • Joint pain

Seizures. Some people who have taken Firdapse have reported having seizures. People with a history of seizures should not take Firdapse. There are many different types of seizures and some of them are not easy to recognize. Stop taking Firdapse and call your health care provider right away if you have any of the following signs that a seizure is happening or could happen.

  • Muscle twitching, jerking, spasms, tremors, or other uncontrolled movements
  • Stiffening of your arms and legs
  • Feeling anxious, nervous, confused, or a sense of dread
  • Feeling dizzy or lightheaded
  • Falling or losing consciousness

Warnings & Precautions

Who should not use Firdapse?

Allergies to Ingredients. People who are allergic to any of the following should not take Firdapse.

  • Amifampridine
  • Amifampridine phosphate
  • Firdapse
  • Ruzurgi
  • Any other medicine known as an aminopyridine, such as compounded 3,4-diaminopyridine
  • Any of the ingredients in the specific product dispensed

Your pharmacist can tell you all of the ingredients in the specific Firdapse products they stock.

History of Seizures. Firdapse should not be used if you have ever had a seizure.

What should I know about Firdapse before using it?

Do not take Firdapse unless it has been prescribed to you by a health care provider. Take it as prescribed. Follow the dosing schedule given by your health care provider. Do not stop taking Firdapse or change your dose unless your health care provider tells you to do so.

Read the Medication Guide before taking Firdapse and each time you get a refill. 

Do not share Firdapse with other people, even if they have the same condition as you. It may harm them.

Firdapse tablets are scored, meaning they have an indentation in the middle that allows them to be split in half for easier dosing if needed. Certain people may need to make a suspension. This includes people with a feeding tube, people who cannot swallow tablets, and people who need to take small doses. If you need to make a suspension, you can find detailed instructions in the Instructions for Use section. You can find all the supplies you need at your local pharmacy. The suspension should only be prepared for one day at a time. Store it in the refrigerator between doses and shake well before each use. 

Keep Firdapse out of the reach of children. If you prepare the suspension, you will need to store it in the refrigerator. Take special precautions to keep it away from children who also use the refrigerator.

What should I tell my health care provider before using Firdapse?

Tell your health care provider about all of your health conditions and any prescription or over-the-counter (OTC) medicines, vitamins/minerals, herbal products, and other supplements you are using. This will help them determine if Firdapse is right for you.

In particular, make sure that you discuss any of the following.

Current and Past Health Conditions. Tell your health care provider if you have any of the following.

  • Liver problems
  • Kidney problems
  • Seizures
  • Your health care provider has told you that you are a poor metabolizer of N-acetyltransferase 2 (NAT2)

Other Medicines and Supplements. Firdapse may interact with other medicines and supplements. Before taking Firdapse, tell your health care provider about any prescription or over-the-counter (OTC) medicines, vitamins/minerals, herbal products, and other supplements you are using. See the Interactions section for more details

Pregnancy. It is not known if or how Firdapse could affect pregnancy or harm a fetus. Tell your health care provider if you are pregnant or plan to become pregnant. If you become pregnant while taking Firdapse, you can sign up for the Firdapse Pregnancy Registry by calling 855-212-5856 or at www.firdapsepregnancystudy.com. This registry collects safety information about the use of Firdapse during pregnancy.

Breastfeeding. It is not known if Firdapse passes into breast milk. Tell your health care provider if you are breastfeeding or plan to breastfeed. Your health care provider will let you know if you should take Firdapse while breastfeeding.

How can I get more information about Firdapse?

For more information about Firdapse, you can visit the drugmaker’s website at www.firdapse.com or call them at 833-422-8259.

Interactions

Does Firdapse interact with foods or drinks?

There are no known interactions between Firdapse and foods or drinks.

It is unknown if drinking alcohol will affect Firdapse.

Does Firdapse interact with other medicines (drug interactions)?

Always tell your health care provider about any prescription or over-the-counter (OTC) medicines, vitamins/minerals, herbal products, and other supplements you are using.

In particular, make sure that you discuss if you are using any of the following before taking Firdapse.

  • Bupropion (Aplenzin, Wellbutrin SR, Wellbutrin XL, and others), which is a medicine used to treat depression or to help quit smoking
  • Tramadol (Conzip), which is a medicine used to treat pain
  • A tricyclic antidepressant, such as amitriptyline, nortriptyline, or protriptyline, even if it is not used for depression
  • Theophylline (Elixophyllin, Theo-24), which is a medicine for asthma or certain other breathing problems
  • An anticholinergic medicine, which includes antihistamines and medicines commonly used for overactive bladder, Parkinson’s disease, or stomach problems

This may not be a complete list of medicines that can interact with Firdapse. Always check with your health care provider.

Does interact with other drugs you are taking?

Enter your medication into the WebMD interaction checker

Overdose/Missed Dose

What should I do if I accidentally use too much Firdapse?

If you or someone else has used too much Firdapse, get medical help right away, call 911, or contact a Poison Control center at 800-222-1222.

What should I do if I miss a dose of Firdapse?

If you miss a dose, skip the missed dose. Take the next dose at your regular scheduled time. Do not take double or extra doses.