ABSTRACT
OBJECTIVE:
Using data pooled from several studies of dalfampridine extended release (ER), a population pharmacokinetic model was developed for the purposes of characterizing the population pharmacokinetics and pharmacodynamics of dalfampridine ER with respect to variability in pharmacokinetics, covariates affecting the pharmacokinetics, and whether the current therapeutic dosage represents an optimal dosage. Studies were conducted in healthy volunteers and multiple sclerosis (MS) patients over the course of development and registration of dalfampridine extended release tablets (dalfampridine ER [Ampyra *]; prolonged, modified or sustained-release fampridine [Fampyra †] in some countries).

METHODS:
The model used to best describe the population pharmacokinetics of dalfampridine-ER was an open, one-compartment model with first-order absorption, first-order elimination and an absorption lag time.

RESULTS:
The population median estimated oral clearance was 36 L/h for a 50-year-old woman with a creatinine clearance of 105 mL/min and 42 L/h for a comparable man. The typical volume of distribution was 304 L for women and 403 L for men. The estimated absorption rate constant was 1.22 hours(-1) in the fasted state and 2.22 hours(-1) when given with food. The covariates identified as having a significant effect (p < 0.01) on model fit were food and gender on absorption rate, and gender, age and creatinine clearance on oral clearance. Only creatinine clearance and age are of clinical relevance. Concomitant medications did not affect any of the parameters in the model. Exposure-response relationships for both efficacy and safety were consistent with what has been observed in clinical trials. Limitations of this study include some reliance on unpublished data, and the limited effectiveness of the model for determining the likelihood of the efficacy and safety of dalfampridine-ER in clinical practice.

CONCLUSIONS:
The approved therapeutic dosage regimen of dalfampridine ER 10 mg twice daily was identified as the optimum dosing regimen based on model predicted exposure response relationships for efficacy and adverse events. A limitation of this study is the limited effectiveness of the models used to predict long-term efficacy and safety of dalfampridine ER in clinical use.