Dalfampridine (Page 2 of 5)

6.2 Postmarketing Experience

The following adverse reactions have been identified during post approval use with dalfampridine. Because these reactions are reported voluntarily from a population of uncertain size, it is not always possible to reliably estimate their frequency or establish a causal relationship to drug exposure: vomiting, vertigo.

7 DRUG INTERACTIONS

7.1 OCT2 Inhibitors

Concurrent treatment with OCT2 inhibitors, such as cimetidine, may cause increased exposure to dalfampridine [see Clinical Pharmacology (12.3)]. Elevated levels of dalfampridine increase the risk of seizures [see Warnings and Precautions (5.1, 5.2)]. The potential benefits of taking OCT2 inhibitors concurrently with dalfampridine should be considered against the risk of seizures in these patients.

7.2 Baclofen

No interaction was identified between dalfampridine and baclofen [see Clinical Pharmacology (12.3)].

8 USE IN SPECIFIC POPULATIONS

8.1 Pregnancy

Risk Summary

There are no adequate data on the developmental risk associated with use of dalfampridine in pregnant women. Administration of dalfampridine to animals during pregnancy and lactation resulted in decreased offspring viability and growth at clinically relevant doses [see Data]. In the U.S. general population, the estimated background risk of major birth defects and miscarriage in clinically recognized pregnancies is 2 to 4% and 15 to 20%, respectively. The background risk of major birth defects and miscarriage for the indicated population is unknown.

Data

Animal Data

Oral administration of dalfampridine to pregnant rats and rabbits throughout organogenesis resulted in no evidence of developmental toxicity in either species. The highest doses tested (10 mg/kg/day in rats, 5 mg/kg/day in rabbits), which were associated with maternal toxicity, are approximately 5 times the MRHD on a body surface area (mg/m2) basis.

Oral administration of dalfampridine (0, 1, 3, and 9 to 6 mg/kg/day; high dose reduced during the second week of dosing) to female rats throughout pregnancy and lactation resulted in decreased offspring viability at the highest dose tested and decreased body weight in offspring at the mid and high doses. The no-effect dose for pre- and postnatal developmental toxicity in rats (1 mg/kg/day) is less than the MRHD on an mg/m2 basis.

8.2 Lactation

Risk Summary

There are no data on the presence of dalfampridine in human milk, the effects of dalfampridine on the breastfed infant, or the effects on milk production. The developmental and health benefits of breastfeeding should be considered along with the mother’s clinical need for dalfampridine and any potential adverse effects on the breastfed infant from dalfampridine or from the underlying maternal condition.

8.4 Pediatric Use

Safety and effectiveness in patients younger than 18 years of age have not been established.

8.5 Geriatric Use

Clinical studies of dalfampridine did not include sufficient numbers of subjects aged 65 and over to determine whether they respond differently than younger subjects. A population PK analysis showed that dalfampridine clearance modestly decreased with increasing age, but not sufficiently to necessitate a modification of dose with age. Other reported clinical experience has identified no differences in responses between the elderly and younger patients.

Dalfampridine is known to be substantially excreted by the kidneys and the risk of adverse reactions, including seizures, is greater with increasing exposure of dalfampridine. Because elderly patients are more likely to have decreased renal function, it is particularly important to know the estimated creatinine clearance (CrCl) in these patients [see Warnings and Precautions (5.2)].

8.6 Impaired Renal Function

Clearance of dalfampridine is decreased in patients with renal impairment and is significantly correlated with creatinine clearance (CrCl) [see Clinical Pharmacology (12.3)]. Dalfampridine is contraindicated in patients with moderate or severe renal impairment (CrCl ≤50 mL/min) [see Contraindications (4)]. The risk of seizures in patients with mild renal impairment (CrCl 51 to 80 mL/min) is unknown, but dalfampridine plasma levels in these patients may approach those seen at a dose of 15 mg twice daily, a dose that may be associated with an increased risk of seizures. If unknown, estimated creatinine clearance should be calculated prior to initiating treatment with dalfampridine [see Dosage and Administration (2.3) and Warnings and Precautions (5.2)].

10 OVERDOSAGE

Three cases of overdose were reported in controlled clinical trials with dalfampridine, involving two MS patients. The first patient took six times the currently recommended dose (60 mg) and was taken to the emergency room with altered mental state. The second patient took 40 mg doses on two separate occasions. In the first instance, she experienced a complex partial seizure and, in the second instance, a period of confusion. Both patients recovered by the following day without sequelae.

Several cases of overdose are found in the scientific literature in which various formulations of dalfampridine were used, resulting in numerous adverse events including seizure, confusion, tremulousness, diaphoresis, and amnesia. In some instances, patients developed status epilepticus, requiring intensive supportive care and were responsive to standard therapy for seizures. In one published case report, an MS patient who ingested 300 mg of 4-aminopyridine (dalfampridine) developed a condition that resembled limbic encephalitis. This patient developed weakness, reduced awareness, memory loss, hypophonic speech, and temporal lobe hyperintensities on MRI. The patient’s speech and language and ambulation improved over time, and an MRI at 4 months after the overdose no longer showed signal abnormalities. At one year, the patient continued to have difficulty with short term memory and learning new tasks.

11 DESCRIPTION

Dalfampridine, USP is a potassium channel blocker, available in a 10 mg tablet strength. Each tablet contains 10 mg dalfampridine, formulated as an extended-release tablet for twice-daily oral administration. Dalfampridine, USP is also known by its chemical name, 4-aminopyridine, with the following structure:

Chemical Structure

Dalfampridine extended-release tablets are available in a 10 mg strength and are white to off-white, biconvex, oval shaped, film-coated, unscored tablets, debossed with “WPI ” on one side and “2533 ” on the other side, containing 10 mg of dalfampridine. Inactive ingredients consist of colloidal silicon dioxide, dibasic calcium phosphate, hypromellose, magnesium stearate, polyethylene glycol, and titanium dioxide.

Dalfampridine, USP is a fine white powder with a molecular weight of 94.1, CAS 504-24-5, and a molecular formula of C5 H6 N2 . At ambient conditions, dalfampridine is soluble in water and methanol, sparingly soluble in acetone, 2-butanone, ethyl acetate, dichloromethane, ethanol, isopropanol alcohol and isobutyl alcohol; slightly soluble in toluene and diisopropyl ether; very slightly soluble in hexane and heptane.

12 CLINICAL PHARMACOLOGY

12.1 Mechanism of action

The mechanism by which dalfampridine exerts its therapeutic effect has not been fully elucidated. Dalfampridine is a broad spectrum potassium channel blocker. In animal studies, dalfampridine has been shown to increase conduction of action potentials in demyelinated axons through inhibition of potassium channels.

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