KCNH2 and myeloid sarcoma: In a dose-ranging study of fampridine sustained-release (fampridine-SR) in patients with MS, which included a pharmacokinetic analysis, the therapeutic dose of 10 mg twice daily resulted in mean steady-state plasma concentrations of 0.243 ± 0.113 μM [2], which is 4 orders of magnitude lower than the IC50 for hERG.