- History of a poor response to 3 or more medications for diabetic peripheral neuropathy (DPN), with poor response is defined as treatment with medications in the following categories of therapy for at least 1 month at therapeutic dosages without at least moderate improvement, as judged by the study doctor: antiepileptic drugs, tricyclic antidepressants, serotonin norepinephrine reuptake inhibitors (SNRIs), opioid analgesics, or lidocaine patch