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Posted by on Jan 24, 2010 in Neurology, Pharma

“Walking Drug” Approved for All MS Patients

“Walking Drug” Approved for All MS Patients

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Friday the FDA announced its approval of dalfampridine* (Ampyra; Acorda/Elan) to improve walking in all patients with multiple sclerosis. The drug, in the form of a sustained-release 10-mg tablet, has been assessed in at least 4 well-controlled MS trials; but a non-sustained-release version of the drug, which is believed to enhance nerve conduction by blocking potassium (or possibly, calcium) channels, has been clinically studied in MS since at least 1990.**

The overriding theme of these earlier trials was that the compound has a narrow therapeutic windowmeaning that it improves mobility, but drug toxicity (ie, seizures, acute confusion) is associated with fickle serum-concentration spikes. This observation was the rationale for developing a sustained-release formulation, which is intended to produce adequate drug concentrations while averting the toxicity-inducing peak levels.

According to Ampyra’s prescribing information, approval is based on 2, 14-week, multicenter, randomized placebo-controlled trials conducted in North America: a double-blind phase 3 study (N = 301) and a sequential single-/double-blind study (N = 239). Efficacy is supported by significantly improved speeds of a timed 25-foot walk in about one quarter to one third of treated patients (the percentage differences between dalfampridine- and placebo-treated patients). Positive effects on ambulation were seen in all forms of MS.

Although the Ampyra label does not carry a so-called black-box warning, the FDA advises of the risk of seizures, particularly in patients taking higher-than-recommended doses and in individuals with renal dysfunction. (Last time I checked, the baseline risk of seizure in MS patients was about 5%.) The maximum recommended dosage of the drug is 10 mg (1 tablet) every 12 hours. The label also states that a routine injection of interferon beta-1b (ie, Betaseron or Extavia) does not interfere with the pharmacokinetics of Ampyra.

Share prices of Acorda spiked at end-of-day trading on Friday, after momentarily plunging in mid-October when the FDA questioned the drug’s safety and the meaningfulness of the trials’ outcomes.

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* Aka pyridine-4-amine, 4-aminopyridine, 4-pyridinamine, 4-pyridylamine, and fampridine.

** A directed PubMed search reveals that the first well-controlled trial of 4-aminopyridine was published in 1990 (Polman CH et al. 4-Aminopyridine in multiple sclerosis. Ann Neurol. 1990;28:589). 

bmartin (1130 Posts)

A native East Tennessean, Barbara Martin is a formerly practicing, board-certified neurologist who received her BS (psychology, summa cum laude) and MD from Duke University before completing her postgraduate training (internship, residency, fellowship) at the Hospital of the University of Pennsylvania in Philadelphia. She has worked in academia, private practice, medical publishing, drug market research, and continuing medical education (CME). For the last 3 years, she has worked in a freelance capacity as a medical writer, analyst, and consultant. Follow Dr. Barbara Martin on and Twitter.