Letter to the Editor: A Clarification on Dalfampridine (Ampyra) Dosing and Other Data

I read with interest your recent article entitled, “Advancements in MS Therapy” in the January/February issue of Practical Neurology. Your brief assessment of dalfampridine, formerly known as fampridine, is very timely; however, I would like to clarify several statements made in the paper, including an important patient safety issue.

On page 28, the fourth paragraph describes the maximum recommended dosage of dalfampridine as “two 10mg extended-release tablets taken twice daily.” This is incorrect, and is twice the recommended maximum dose, which is one 10mg tablet twice daily, approximately 12 hours apart. The package insert warns of an increased incidence of seizures at doses of 20mg twice daily. It is extremely important that the maximum recommended dosage of 10mg twice daily not be exceeded.¹

The second paragraph on page 27 notes that clinical trials of dalfampridine were conducted with patients who were not receiving immunomodulatory therapy. I would like to point out that, in two phase III clinical trials of dalfampridine, 63 percent of patients were receiving concurrent immunomodulatory therapy.¹ Concurrent use of immunomodulators is correctly described on page 28.

Also on page 27, it is stated that compounded 4- aminopyridine products “lack consistency and do not have reliable safety—a concern, given potential effects on the QT interval.” While it is well known that compounded 4-aminopyridine is inconsistent in composition and produces rapid, high peak plasma levels characterisitic of immediate release formulations, QT prolongation is not of particular concern. The greater concern is adverse events related to high peak plasma levels, such as seizure. Prolongation of the QT interval has not been associated with dalfampridine;¹ and in fact, the lack of effect on duration of QRS interval is correctly noted in the previous paragraph.

The first paragraph on page 29 states that one quarter of patients may be expected to respond to therapy. In the two phase III trials, responder rates were 35 percent and 43 percent for patients treated with dalfampridine.¹

Thank you for helping to assure than Ampyra is used safely.

—Herbert R. Henley, III, PharmD Vice President, Medical Affairs Acorda Therapeutics

1. Ampyra package insert. Hawthorne, NY: Acorda Therapeutics; January 2010.