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Firdapse
Amifampridine (phosphate)
$10005.00
10mg · 3 × 100 tablets · 3 months supply
BrandBranded medicine· By SERB
$3335.00 per month
How long a supply?
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Annual cost
$36685a year at this pack size
Prescription required
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About Firdapse
Overview
Firdapse is a prescription tablet containing amifampridine as amifampridine phosphate. It is used to treat Lambert-Eaton myasthenic syndrome (LEMS) in adults and children aged 6 years and older. It blocks potassium channels, but exactly how this produces its treatment effect in LEMS is not fully understood.
What it treats
Lambert-Eaton myasthenic syndrome (LEMS) in adults and children aged 6 years and older.
Safety information
Side effects
Common side effects include tingling or prickling sensations, upper respiratory tract infections, abdominal pain, nausea, diarrhea, headache, raised liver enzymes, back pain, high blood pressure, and muscle spasms. Firdapse can cause seizures and serious allergic reactions, including anaphylaxis. Seek immediate medical attention if either occurs. If an allergic reaction occurs, Firdapse should be stopped and appropriate treatment started. If a seizure occurs, the prescriber may reduce or stop treatment.
When to call your doctor
If symptoms are severe or getting worse quickly, seek emergency care rather than waiting.
Before taking this medicine
Do not take Firdapse if you have a history of seizures or are allergic to amifampridine phosphate or another aminopyridine. Firdapse can cause seizures. If a seizure occurs during treatment, the prescriber may consider reducing the dose or stopping treatment. If an allergic reaction occurs, including anaphylaxis, Firdapse should be stopped and appropriate treatment started. Use during pregnancy requires caution: animal studies suggest Firdapse may harm the unborn baby.
Interactions
Tell your doctor if you take medicines that lower the seizure threshold, as taking them with Firdapse may increase the risk of seizures. Medicines with cholinergic effects, such as direct or indirect cholinesterase inhibitors, may increase the cholinergic effects of both Firdapse and those medicines when taken together, raising the risk of side effects.
Using Firdapse
Dosing
Dosing is set by your prescriber. Each health care professional may prescribe medication differently according to a patient's medical history and condition, so follow the directions on your prescription label and speak to your doctor or pharmacist before changing anything.
Storage
Store below 25°C in a dry place, in the original pack, away from direct light and moisture. Do not keep it in a bathroom. Keep all medicines out of the sight and reach of children.
Clinical information on this page is summarised from the US FDA label FIRDAPSE (AMIFAMPRIDINE PHOSPHATE) TABLET [CATALYST PHARMACEUTICALS, INC.] (DailyMed, retrieved 19 September 2026).
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