amifampridine phosphate (Rx)

Brand and Other Names:Firdapse
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Dosing & Uses

AdultPediatricGeriatric

Dosage Forms & Strengths

tablet

  • 10mg

Lambert-Eaton Myasthenic Syndrome

Indicated for Lambert-Eaton myasthenic syndrome (LEMS)

15-30 mg/day PO in divided doses (3-4 times daily) initially; may increase by 5 mg/day q3-4 days; not to exceed 80 mg/day

Maximum single dose: 20 mg

Dosage Modifications

Renal impairment

  • CrCl 15-90 mL/min: Recommended starting dose is 15 mg/day PO in 3 divided doses; monitor closely; consider dosage modification or discontinuation if needed based on effect and tolerability
  • End-stage renal disease (CrCl <15 mL/min): No recommendation can be made

Hepatic impairment

  • Not studied
  • Extensively metabolized by N-acetyltransferase 2 (NAT2), and hepatic impairment may cause an increase in exposure
  • Recommended starting dose: 15 mg/day PO in 3 divided doses; monitor closely
  • Consider dosage modification or discontinuation if needed based on effect and tolerability

NAT2 poor metabolizers

  • Recommended starting dose: 15 mg/day PO in 3 divided doses; monitor closely
  • Consider dosage modification needed based on clinical effect and tolerability

Myasthenia Gravis (Orphan)

Orphan designation for treatment of myasthenia gravis

Sponsor

  • Catalyst Pharmaceuticals, Inc; 355 Alhambra Circle Suite 1250; Coral Gables, Florida 33134

Lambert-Eaton myasthenic syndrome (LEMS): Safety and efficacy not established

Congenital Myasthenic Syndromes (Orphan)

Orphan designation for treatment of congenital myasthenic syndromes

Sponsor

  • Catalyst Pharmaceuticals, Inc; Suite 1500; Coral Gables, Florida 33134

In general, dose selection for an elderly patient should be cautious, usually starting at the low end of the dosing range, reflecting the greater frequency of decreased hepatic, renal, or cardiac function, and of concomitant disease or other drug therapy

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Interactions

Interaction Checker

and amifampridine phosphate

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            Adverse Effects

            >10%

            Paresthesia (62%)

            Upper respiratory tract infection (33%)

            Abdominal pain (14%)

            Nausea (14%)

            Diarrhea (14%)

            Headache (14%)

            Elevated liver enzymes (14%)

            Back pain (14%)

            Hypertension (12%)

            Muscle spasms (12%)

            1-10%

            Dizziness (10%)

            Asthenia (10%)

            Muscular weakness (10%)

            Pain in extremity (10%)

            Cataract (10%)

            Constipation (7%)

            Bronchitis (7%)

            Fall (7%)

            Lymphadenopathy (7%)

            Seizures (2%)

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            Warnings

            Contraindications

            History of seizures

            Hypersensitivity to amifampridine phosphate or another aminopyridine

            Cautions

            If hypersensitivity reaction (eg, anaphylaxis) occurs, discontinue drug and initiate appropriate therapy

            Seizures

            • Can cause seizures; consider discontinuation or dose reduction in patients who have a seizure while on treatment
            • Many instances of seizure were in patients taking medications or who had comorbid conditions that may have lowered seizure threshold
            • Contraindicated in patients with history of seizures

            Drug interactions overview

            • Drugs that lower seizure threshold: Coadministration may increase risk of seizures
            • Drugs with cholinergic effects: Coadministration may increase risk of adverse cholinergic effects
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            Pregnancy

            Pregnancy

            No data are available in pregnant women

            Based on animal studies, can cause fetal harm (eg, still births, reduced fetal weight, delayed sexual development) at doses associated with maternal plasma drug levels lower than therapeutic drug levels

            Lactation

            Unknown if distributed in human breast milk

            In lactating rats, amifampridine was excreted in milk and reached levels similar to those in maternal plasma

            Consider the developmental and health benefits of breastfeeding along with the mother’s clinical need for the drug, and any potential adverse effects on the breastfed infant from the drug or from the underlying maternal condition

            Pregnancy Categories

            A:Generally acceptable. Controlled studies in pregnant women show no evidence of fetal risk.

            B:May be acceptable. Either animal studies show no risk but human studies not available or animal studies showed minor risks and human studies done and showed no risk.

            C:Use with caution if benefits outweigh risks. Animal studies show risk and human studies not available or neither animal nor human studies done.

            D:Use in LIFE-THREATENING emergencies when no safer drug available. Positive evidence of human fetal risk.

            X:Do not use in pregnancy. Risks involved outweigh potential benefits. Safer alternatives exist.

            NA:Information not available.

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            Pharmacology

            Mechanism of Action

            Blocks voltage-dependent potassium channels, thereby prolonging presynaptic cell membrane depolarization, which enhances calcium transport into nerve endings

            The increased intracellular calcium concentrations facilitate exocytosis of acetylcholine-containing vesicles, which, in turn, enhances neuromuscular transmission

            Absorption

            Peak plasma time: 20-60 minutes

            AUC, Cmax, and Cmin were highly variable between individuals following single and multiple doses

            Metabolism

            Extensively metabolized by N-acetyltransferase gene 2 (NAT2) in the liver to 3-N-acetyl-amifampridine (inactive)

            Elimination

            Half-life: 1.8-2.5 hr (healthy volunteers)

            Excretion: 93-100% in urine as amifampridine or inactive metabolite

            Pharmacogenetics

            Genetic variants in NAT2 affect rate and extent of metabolism

            Poor metabolizers (ie, carriers of 2 reduced-function alleles) have 3.5- to 4.5-fold higher Cmax and 5.6- to 9-fold higher AUC than normal or fast metabolizers (ie, fast acetylators)

            In the general population, the NAT2 poor metabolizer phenotype prevalence is 40-60% in white and African American populations and 10-30% in Asian ethnic populations

            See Dosage Modifications

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            Administration

            Oral Administration

            May administer with or without food

            Missed dose: Do not take double or extra doses

            Storage

            Store at 68-77°F (20-25°C); excursions permitted from 15-30°C (59-86°F)

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            Formulary

            FormularyPatient Discounts

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            The above information is provided for general informational and educational purposes only. Individual plans may vary and formulary information changes. Contact the applicable plan provider for the most current information.

            Tier Description
            1 This drug is available at the lowest co-pay. Most commonly, these are generic drugs.
            2 This drug is available at a middle level co-pay. Most commonly, these are "preferred" (on formulary) brand drugs.
            3 This drug is available at a higher level co-pay. Most commonly, these are "non-preferred" brand drugs.
            4 This drug is available at a higher level co-pay. Most commonly, these are "non-preferred" brand drugs or specialty prescription products.
            5 This drug is available at a higher level co-pay. Most commonly, these are "non-preferred" brand drugs or specialty prescription products.
            6 This drug is available at a higher level co-pay. Most commonly, these are "non-preferred" brand drugs or specialty prescription products.
            NC NOT COVERED – Drugs that are not covered by the plan.
            Code Definition
            PA Prior Authorization
            Drugs that require prior authorization. This restriction requires that specific clinical criteria be met prior to the approval of the prescription.
            QL Quantity Limits
            Drugs that have quantity limits associated with each prescription. This restriction typically limits the quantity of the drug that will be covered.
            ST Step Therapy
            Drugs that have step therapy associated with each prescription. This restriction typically requires that certain criteria be met prior to approval for the prescription.
            OR Other Restrictions
            Drugs that have restrictions other than prior authorization, quantity limits, and step therapy associated with each prescription.
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            Medscape prescription drug monographs are based on FDA-approved labeling information, unless otherwise noted, combined with additional data derived from primary medical literature.