FDA warns of seizure risk for multiple sclerosis patients who take dalfampridine

On July 23, 2012, FDA announced a safety communication regarding the risk of seizures in patients with multiple sclerosis (MS) starting dalfampridine (Ampyra). Ampyra was approved by FDA in 2010 to improve walking in patients with MS. The safety communication stemmed from a review of post-marketing adverse event reports.

Seizures are a known risk of dalfampridine therapy at the approved dose of 10 mg twice daily. According to FDA, most post-marketing cases occurred days to weeks after starting therapy and in patients with no known history of seizures. The risk of seizures increases with increasing drug concentrations and given that dalfampridine is cleared renally, patients with even mild renal impairment [creatinine clearance (CrCl) of 51 mL/min to 80 mL/min] can accumulate the drug to levels which may precipitate a seizure.

FDA reminds clinicians that mild renal impairment in patients over aged 50 years is common due to an age-associated decline in kidney function. For this reason, patients with a CrCl of 51 mL/min to 80 mL/min are considered to be at an increased risk of seizures. FDA warns clinicians to weigh the risks versus benefits of therapy carefully in the patient population.

"The risk of seizures on [dalfampridine] is not a new finding, however, this safety communication highlights the importance of appropriate patient selection for the use of dalfampridine, as well as proper monitoring," Diana Sobieraj, PharmD, assistant professor at the University of Connecticut School of Pharmacy, Storrs, Conn., told Formulary. "Patient education is also paramount since this is an extended-release formulation, patients should be aware that taking the tablet whole-and not trying to 'catch up' if they miss a dose-will help to assure proper drug concentrations."

SOURCES

1. FDA Drug Safety Communication: Seizure risk for multiple sclerosis patients who take Ampyra (dalfampridine) Available at: http://www.fda.gov/Drugs/DrugSafety/ucm312846.htm Accessed July 26, 2012.

2. Ampyra [package insert]. FDA. Available at: http://www.accessdata.fda.gov/drugsatfda_docs/label/2012/022250s003s004lbl.pdf. Accessed July 26, 2012.