The study will be conducted at all centres participating in the TEC-006 study. Patients may receive repeated cycles of treatment with tetrodotoxin. Each Treatment Cycle will consist of 4 days of treatment with 30 μg b.i.d. of tetrodotoxin injected subcutaneously. Each Treatment Cycle will last from the start of treatment to the end of the analgesic response. All patients completing the first Treatment Cycle in this protocol must meet the criteria of the Responder (First TEC-006OL Treatment Cycle) definition in order to be eligible for a second Treatment Cycle. Patient eligibility for all subsequent Treatment Cycles will be determined using the eligibility criteria for a Repeated Treatment Cycle.