Research Study to Test Safety and Effectiveness of Investigational Drug in Patients With Trigeminal Neuralgia

Inclusion Criteria: * Age 18 - 75 yrs * Male; or non-pregnant/non-lactating female * Use of adequate birth-control measures as determined by investigator for females of child-bearing potential * Diagnosis of trigeminal neuralgia (TN) using IHS (International Headache Society) criteria (see appendix A) * Able to cooperate with and understand study instructions * Signed informed consent prior to entering study * Patients must be on a stable dose of concomitant medications for treatment of trigeminal neuralgia (TN) for at least 4 weeks (see below) * If subject is currently receiving a tricyclic antidepressant, anticonvulsant, and/or Class I antiarrhythmic (e.g., amitriptyline, mexiletine, phenytoin, gabapentin or carbamazepine) for treatment of pain or any other condition, subject must be willing and able to maintain stable doses of these agents within 4 weeks prior to randomization and throughout the study (i.e., doses cannot be increased or decreased during this period). * Subjects who require "rescue" analgesic medication during the study will be allowed to use increased doses of their current (pre-study) opioid and/or non opioid analgesics as clinically indicated (e.g., non-steroidal anti-inflammatory medications, acetaminophen, COX-2 inhibitors, topical analgesics). Subjects will be allowed to use a new analgesic for a limited time for non-neuropathic pain (e.g., headache, sinusitis, strained muscle, minor ache and pain), but will be prohibited from initiating therapy with a new analgesic agent and use it continuously throughout the remainder of the study. * If subject is not currently receiving a tricyclic antidepressant, anticonvulsant, and/or Class I antiarrhythmic (e.g., amitriptyline, mexiletine, phenytoin, gabapentin or carbamazepine) for treatment of pain or any other condition, subject must be willing and able to abstain from initiation of these agents within 4 weeks prior to randomization and throughout the study. * Subject must be willing and able to abstain from initiating an alternative therapy (e.g., acupuncture, massage or physical therapy) for pain relief during the study. (NOTE: subjects who are currently using alternative therapy for pain relief can be enrolled if they are willing and able to maintain such therapy stable throughout the study.) Exclusion Criteria: * Serious hepatic, respiratory, hematologic, cardiovascular or renal condition * Neurologic pain other than TN (trigeminal neuralgia), with the exception of occasional migrainous/ tension-type headaches. (\<4 headaches per month) * Psychiatric or medical condition that might compromise participation in study, as determined by the investigator * Use of opioid analgesic as treatment of neuralgia (\>2 days per week) * Administration of any investigational drug within 30 days prior to screening * Concurrent use of sodium valproate * Current diagnosis of active epilepsy or any active seizure disorder requiring chronic therapy with antiepileptic drug(s) * Pregnant or breastfeeding women * History of substance abuse/ alcoholism