Ruzurgi (Amifampridine) for LEMS

Last updated Jan. 9, 2023, by Teresa Carvalho, MS

✅ Fact-checked by Joana Carvalho, PhD

What is Ruzurgi for Lambert-Eaton myasthenic syndrome?

Ruzurgi (amifampridine, also called 3,4-diaminopyridine or 3,4-DAP) is an oral potassium channel blocker that was approved in the U.S. and Canada to ameliorate muscle strength in children with Lambert-Eaton myasthenic syndrome (LEMS).

However, the therapy is no longer available in either country as a treatment for LEMS.

In February 2022, its approval in the U.S. was canceled for violating the market exclusivity rights of Firdapse, a similar therapy with the same active ingredient that had been approved previously for adults with LEMS.

In March 2022, Ruzurgi’s approval in Canada was suspended for the second time.

The therapy was developed by Jacobus Pharmaceutical.

How does Ruzurgi work?

LEMS is a rare autoimmune disease in which the immune system generates autoantibodies against a protein called voltage-gated calcium channel (VGCC) found in nerve cell endings. Calcium channels are required for the release of acetylcholine, a neurotransmitter or cell signaling molecule that initiates a cascade of events leading to muscle contraction.

In patients with LEMS, little acetylcholine is released in response to nerve signals. Without sufficient acetylcholine to promote muscle contraction, muscles tend to weaken over time and patients become easily fatigued.

Amifampridine, Ruzurgi’s active ingredient, binds to voltage-gated potassium channels. By blocking these channels, Ruzurgi prevents nerve cells from resetting after a nerve signal has been sent, giving more time for the small number of healthy VGCCs that remain to stay open. This in turn can increase the amount of acetylcholine that is released from nerve cell endings, and thereby increase muscle strength.

Who can take Ruzurgi?

Ruzurgi was authorized in the U.S. in 2019, and was the first treatment approved by the U.S. Food and Drug Administration (FDA) for children, ages 6 to 16, with LEMS. The therapy also was approved in Canada one year later. However, its approval was revoked in both countries in 2022, making it no longer available.

Who should not take Ruzurgi?

Ruzurgi was contraindicated, or not recommended, for patients who have had allergic reactions to the treatment or to any of its ingredients. These ingredients included:

  • colloidal silicon dioxide.
  • dibasic calcium phosphate dihydrate.
  • magnesium stearate.
  • microcrystalline cellulose.
  • sodium starch glycolate.

People with a history of seizures should not take Ruzurgi. The therapy also was contraindicated for patients taking other forms of amifampridine, or other aminopyridines.

How was Ruzurgi administered?

Ruzurgi was available as an oral treatment in tablets containing 10 mg of amifampridine.

Patients ages 6 and older and weighing at least 45 kg (about 99 lbs) were to start with 15 to 30 mg daily, in divided doses (two to three times daily). The maximum single dose was 30 mg and the maximum daily dosage was 100 mg.

For those 6 years old and older but weighing less than 45 kg, Ruzurgi was initially given at 7.5 to 15 mg daily, in divided doses (two to three times daily). The maximum single dose was 15 mg and the maximum daily dosage was 50 mg.

A suspension of 1 mg/mL could be prepared and administered by mouth or feeding tube to patients who had difficulty swallowing, or required assisted feeding.

Ruzurgi in clinical trials

The decision to approve Ruzurgi for children and adolescents with LEMS was originally based on clinical data collected from adult patients, combined with simulations to find the best dose for children. Data were collected from a Phase 2 trial called DAPPER (NCT01511978).

DAPPER trial

DAPPER included 32 adults with LEMS who had been taking Ruzurgi for at least three months as part of an FDA-approved compassionate use program.

Patients were randomly assigned to continue treatment with Ruzurgi at a daily dose of 30–100 mg (divided into three doses), or to a placebo.

The trial evaluated changes in the time it takes for a patient to rise from a chair, walk a short distance, and return to the chair three times without pause. Results showed that patients who remained on Ruzurgi experienced fewer impairments when performing these tasks compared with those who switched to the placebo. Additionally, patients who switched to the placebo reported a greater feeling of muscle weakness compared with those who remained on Ruzurgi.

Common side effects of Ruzurgi

The most common side effects associated with Ruzurgi included:

  • a burning or prickling sensation.
  • abdominal pain.
  • indigestion.
  • dizziness.
  • nausea.

Allergic reactions

Ruzurgi may have potentially caused allergic reactions, such as anaphylaxis, which can be serious and life-threatening. In such cases, the medication should have been stopped and appropriate treatment administered.


Patients may have experienced seizures while on Ruzurgi, including those without a history of such episodes. In those cases, patients were recommended to stop taking the medication or lower its dosage.

Use in patients with other conditions

Ruzurgi should be cautiously used by patients with other conditions, such as liver disease, heart problems, and kidney failure.

Use with other medications

People who took Ruzurgi alongside anti-seizure medications were more likely to experience seizures. The therapy’s simultaneous use with cholinesterase inhibitors — a group of medicines that block the normal breakdown of acetylcholine — may have increased the cholinergic effects of Ruzurgi and of those medicines, and increase the risk of side effects.

Use in pregnancy and breastfeeding

It was unknown if Ruzurgi could affect the developing fetus or pass to breast milk. Patients planning to become pregnant or breastfeed should have talked with their healthcare team and only continue treatment during these periods if the potential benefits justified the potential risks to the fetus or infant.


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.