FAQs About Firdapse as Treatment for LEMS

Brian Murphy Ph.D. avatar

by Brian Murphy Ph.D. |

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Firdapse is an approved treatment for patients ages 17 and older with Lambert-Eaton myasthenic syndrome or LEMS.

How does Firdapse work?

Firdapse works by improving the ability of nerve cells to communicate with muscle cells. It does this by helping restore the release of acetylcholine, a cell-signaling molecule that causes muscles to contract. In LEMS, the ability of nerve cells to release acetylcholine is reduced due to the body mistakenly attacking nerve cell endings.

How do I take it and how often?

Firdapse comes as scored 10 mg tablets that you should take three or four times a day.

Patients usually start treatment at a dose between 15 and 30 mg per day and slowly increase the amount by 5 mg every three or four days. The pills are scored in the middle to allow you to split them so you can take them at 5 mg increments. Your doctor will guide you on when to increase your dose and, depending on how you respond to the treatment, when to stop increasing it. Once you reach a stable dose level, you enter a phase called maintenance in which you will just continue with that dose.

You can take Firdapse with or without food. You should not take more than two tablets (20 mg) at a time or more than eight tablets (80 mg) in a 24-hour period.

Does it work in all patients?

Firdapse is for all adults with LEMS and adolescent patients who are 17 years old. However, everyone metabolizes it at different rates. Thus, your doctor will modify your dosage to find the right amount for you. In clinical trials, the average daily dose of Firdapse was 60 mg.

What is the difference between Firdapse and Ruzurgi?

Firdapse and Ruzurgi share the same active ingredient, amifampridine. However, this active ingredient is bound to a phosphate molecule in Firdapse and is unattached in Ruzurgi.

What are the side effects?

You may experience a variety of side effects while taking Firdapse. The most serious ones include the risk of seizures and an allergic reaction called anaphylaxis. The most common side effects are tingling around the mouth, face, fingers, toes, and other body parts, upper respiratory tract infections, stomach pain, diarrhea, and headache. Increased liver enzymes, back pain, high blood pressure, and muscle spasms are other common side effects.

Are there reasons I shouldn’t take Firdapse?

You should not take Firdapse if you have ever had a seizure or are allergic to amifampridine or another aminopyridine molecule.

You should discuss the possible complications of taking Firdapse with your doctor if you have kidney or liver problems, you are pregnant or may become pregnant, are breastfeeding or plan to breastfeed, or are taking another aminopyridine.

Researchers have not evaluated the safety and efficacy of Firdapse in patients younger than age 17.

How should I store it?

Firdapse contains phosphorus, which helps make it more stable. Therefore, you do not need to refrigerate the tablets and you can store them at room temperature (68°F to 77°F / 20°C to 25°C) for up to two years.


Last updated: Nov. 30, 2020


Lambert-Eaton News is strictly a news and information website about the disease. It does not provide medical advice, diagnosis, or treatment. This content is not intended to be a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition. Never disregard professional medical advice or delay in seeking it because of something you have read on this website.