Genetic Implications: Genetic Implications


Trade Name(s)

  • Firdapse

Ther. Class.

cholinergic muscle stimulants

Pharm. Class.

potassium channel blockers


Lambert-Eaton myasthenic syndrome (LEMS).


Increases acetylcholine release in nerve terminals via potassium channel blockade.

Therapeutic Effect(s):

Decreased progression of muscle weakness.


Absorption: Rapidly and well absorbed.

Distribution: Widely distributed to tissues.

Metabolism and Excretion: Extensively metabolized by N-acetyltransferase 2 (NAT2) to an inactive metabolite. Primarily eliminated in urine (as either unchanged drug or metabolite).

Half-life: 1.8–2.5 hr.

TIME/ACTION PROFILE (plasma concentrations)

POunknown0.3–1 hrunknown


Contraindicated in:

  • Hypersensitivity to amifampridine or another aminopyridine;
  • History of seizures;
  • Severe renal impairment (CCr ≤15 mL/min) (↑ risk of seizures).

Use Cautiously in:

  • Mild-to-moderate renal impairment (CCr 16–80 mL/min) (initiate with lowest dose and monitor closely);
  • Hepatic impairment (initiate with lowest dose and monitor closely)
  • Genetic implication  NAT2 poor metabolizers (initiate with lowest dose and monitor closely);
  • OB:   Safety not established in pregnancy;
  • Lactation: Use while breastfeeding only if potential maternal benefit justifies potential risk to infant
  • Pedi:  Safety and effectiveness not established in children
  • Geri:  Consider age-related ↓ in renal function.

Adverse Reactions/Side Effects

CV: hypertension, peripheral edema

Derm: erythema

EENT: cataracts

GI: abdominal pain, diarrhea, ↑ liver enzymes, nausea, constipation, dyspepsia

GU: urinary tract infection

Metabolic: hypercholesterolemia

MS: back pain, extremity pain, muscle spasms, muscle weakness, ↑ creatine kinase

Neuro: dizziness, headache, paresthesia, depression, insomnia, SEIZURES, weakness.

Resp: dyspnea

Misc: fever, HYPERSENSITIVITY REACTIONS (including anaphylaxis)

* CAPITALS indicate life-threatening.
Underline indicate most frequent.



  •  Drugs that lower seizure threshold  may ↑ risk of seizures.
  •  Cholinesterase inhibitors (direct or indirect)  may ↑ cholinergic effects.


PO (Adults):  15 to 30 mg/day in 3 to 4 divided doses; may ↑ by 5 mg/day every 3–4 days (not to exceed 20 mg/dose or 80 mg/day).  NAT2 poor metabolizers– 5 mg 3 times daily; may adjust dose or discontinue use based on response and tolerability.

Renal Impairment 
PO (Adults): CCr 15–90 mL/min– 5 mg 3 times daily; may adjust dose or discontinue use based on response and tolerability.

Hepatic Impairment 
(Adults): 5 mg 3 times daily; may adjust dose or discontinue use based on response and tolerability.


Tablets: 10 mg


  • Initiate seizure precautions. If seizures occur, medication may need to be discontinued.
  • Assess stamina and weakness periodically during therapy.


  • PO Administer without regard to food. Scored tablets may be divided in two. Store tablets in refrigerator; protect from light and moisture. Stable for up to 3 mos.
    • May be made into a 1 mg/mL suspension for patients with difficulty swallowing tablets, require a feeding tube, or for doses <5 mg. Place three 10 mg tablets in a 30 mL container, add 30 mL of sterile water and shake well for 30 seconds. Crushing tablets is not necessary. Use an oral syringe to draw up and administer correct dose by mouth or by feeding tube. Refrigerate suspension between doses and shake well before each dose. Suspension can be stored under refrigeration for up to 24 hr. Discard unused portion of suspension after 24 hr.

Patient/Family Teaching

  • Instruct patient to take medication as directed and follow dose escalation schedule. Advise patient to omit missed doses. Do not double doses; may increase risk of seizures. Do not change dose or stop medication without consulting health care professional.
  • Advise patient to notify health care professionals if seizures or signs and symptoms of hypersensitivity reaction (shortness of breath, trouble breathing, swelling of throat or tongue, hives) occur.
  • Instruct patient to notify health care professional of all Rx or OTC medications, vitamins, or herbal products being taken and to consult with health care professional before taking other medications.
  • Rep:  Advise females of reproductive potential to notify health care professional if pregnancy is planned or suspected or if breastfeeding. Inform patient of pregnancy exposure registry that monitors pregnancy outcomes in women exposed to  Firdapse  during pregnancy. Clinicians are encouraged to enroll pregnant patients, or pregnant women may register themselves in the registry by calling 855-212-5856 (toll-free), using the fax number 877-867-1874 (toll-free), by contacting the Pregnancy Coordinating Center at, or by visiting the study website

Evaluation/Desired Outcomes

Improved stamina and decreased weakness in patients with LEMS.