The purpose of this study is to evaluate the effectiveness and safety of tramadol 37.5mg/acetaminophen 325mg compared to gabapentin in patients with diabetic neuropathic pain.

Treatment of painful diabetic neuropathy often requires multiple medications with different mechanisms of action in order to obtain an optimal analgesic effect. Painful diabetic neuropathy may be considered as a combination of nociceptive/neuropathic pain. Gabapentin has been used to treat painful diabetic neuropathy. Tramadol has been proven to be significantly effective on painful diabetic neuropathy and patients treated with tramadol have showed higher scores on physical and social function scales. The study hypothesis is that the treatment effect of tramadol 37.5mg/acetaminophen 325mg group is not inferior compared to that of gabapentin group for treatment of painful diabetic neuropathy. This is a multicenter, randomized, open comparative study to compare the effectiveness and safety between tramadol 37.5mg/acetaminophen 325mg and gabapentin for the treatment of pain in diabetic neuropathy. The patients will be randomized into 2 treatment groups. Tramadol 37.5mg/acetaminophen 325mg(T/A) group will receive 1 tablet before sleep for 3 days, then 1 tablet twice a day for 4 days followed by 1 tablet three times a day for next 7 days. If there is no pain relief, T/A 325mg can be increased up to 8tablets/day for day 15~28, and then the dosage shoud be maintained for day 29~42. Gabapentin(GB) group will receive 300mg before sleep at day 1, 300mg twice a day at day 2, and 300mg three times a day for day 3~7. Then for day 8~14, subject will receive 300mg in the morning, 300mg in the midday, 600mg in the evening. If there is no pain relief, GB can be increased up to 3600mg/day for day 15~28, and then the dosage shoud be maintained for day 29~42. Tramadol/Acetaminophen group will receive 1 tablet for 3 days, 1 tablet 2x/day for 4 days, and 1 tablet 3x/ day for next 7 days. If there is no pain relief, Tramadol/Acetaminophen can be increased up to 8T/day for day 15~28, and then shoud be maintained for day 29~42. Gabapentin group will receive 300mg hs for 3days, 300mg 2x/day for 4 days and 300mg 3x/day for next 7 days. If there is no pain relief, GB can be increased up to 3600mg/day for day 15~28, and then shoud be maintained for day 29~42.

Inclusion Criteria:

• The patient must have painful symmetric neuropathy in the lower limbs which is applicable to both of the following conditions (Decreased sensation of leg to monofilament, none or decreased ankle reflexes or decreased vibratory sensation. One or more of the following pain symptoms: numbness, tingling, paresthesia, burning, shooting pain, stabbing, or lancinating pain)
• The patient must have painful diabetic neuropathy in the lower limbs for 3 months prior to randomization
• The patient must have diagnosis of Type ll diabetes and stable blood sugar level controlled with an oral medication, insulin or diet therapy for 3 months prior to randomization
• The patient must have HbA1c<=10%
• The patient must have pain intensity score of >=4 on NRS for the last 48 hours.

Exclusion Criteria:

• Have previously experienced failure of tramadol treatment or have discontinued tramadol administration due to adverse event
• Have received the prohibited medication in the protocol prior to randomization (e.g., capsaicin, use of systemic steroids, steroid or local anesthetic injections, tramadol HCl or tramadol combination, gabapentin, opioid analgesics, antidepressants, anticonvulsants, alpha-lipoic acid, acupuncture, COX-2 selective inhibitors, long-acting NSAIDs, opioid analgesics, sedative-hypnotics, muscle relaxants, anxiolytics, antipsychotics, TENS, short-acting non-opioid analgesics)
• Neuropathic pain caused by other reasons(e.g., alcohol abuse, connective tissue disease, toxic exposure, infection, neoplasm, ischemia)
• Suffering from painful diabetic neuropathy over 10 years
• Physical damage or disease which may cause abnomal absorption, excessive accumulation, metabolism or excretion disorder of the study medication