Flupirtine is an activator of Kv7 (KCNQ/M) potassium channels that has found clinical use as an analgesic with muscle relaxant properties. Kv7 potassium channels are expressed in axonal membranes and pharmacological activation of these channels may restore abnormal nerve excitability. We have examined the effect of flupirtine on the electrical excitability of myelinated axons in isolated segments of rat sural nerve. Axonal excitability was studied in vitro with the same parameters used by clinical neurophysiologists to assess peripheral nerve excitability in situ. Application of flupirtine in low micromolar concentrations resulted in an increase in threshold current, a reduction of refractoriness and an increase in post-spike superexcitability. These effects are consistent with an increase in Kv7 conductance and membrane hyperpolarization. Flupirtine also enhanced and prolonged the late, long-lasting period of axonal subexcitability that follows a short burst of action potentials. This effect was blocked by XE 991 (10 microM), an antagonist of Kv7 channels. In summary, flupirtine affects measures of excitability that are altered in the myelinated axons of patients with peripheral nerve disorders. This indicates that neuropathies with abnormal nerve excitability parameters corresponding to those affected by flupirtine may benefit from activation of axonal Kv7 potassium channels.