A Study to Compare Safety and Efficacy of Tramadol Hydrochloride/Acetaminophen With Gabapentin in Participants With Diabetic Neuropathy

The purpose of this study is to evaluate the effectiveness and safety of tramadol hydrochloride (HCl) 37.5 miligram (mg)/acetaminophen 325 mg compared to gabapentin in participants with diabetic neuropathic (nerve disorder caused by diabetes mellitus) pain.

This is an open-label (a medical research study in which participants and researchers are told which treatments the participants are receiving, "unblinded"), multi-center and randomized (study drug is assigned by chance) study to compare the effectiveness and safety of tramadol HCl 37.5 mg/acetaminophen 325 mg with gabapentin in participants with diabetic neuropathy. The study will consist of 4 periods: Screening period (up to Day -14), Randomization period (Day 1), Dosage adjustment period (Day 15) and Maintenance period (Day 43). The participants will be randomly assigned to 1 of the 2 treatment groups: tramadol HCl 37.5 mg/acetaminophen 325 mg or gabapentin. Tramadol Hcl/acetaminophen group will receive 1 tablet for 3 days, then 1 tablet twice daily for 4 days followed by 1 tablet thrice daily for next 7 days. If there is no pain relief, the dosage can be increased up to 8 tablets per day for Day 15 to 28, and then the increased dosage will be maintained for Day 29 to 42. Gabapentin group will receive 300 mg on Day 1, 300 mg twice daily on Day 2, and 300 mg thrice daily for Day 3 to 7. Then for Day 8 to 14, participants will receive 300 mg in the morning, 300 mg in the midday and 600 mg in the evening. If there is no pain relief, gabapentin can be increased up to 3600 mg per day for Day 15 to 28, and then the increased dosage will be maintained for Day 29 to 42. Primarily, efficacy will be evaluated by pain intensity using numeric rating scale (NRS). Participants' safety will be monitored throughout the study.

Eligibility Criteria:
Inclusion Criteria:

* Participants having painful symmetric neuropathy (a disturbance in the function of the brain or spinal cord that may affect the nerves and muscles of the body) in the lower limbs applicable to both of the following conditions: decreased sensation of leg to monofilament, none or decreased ankle reflexes or decreased vibratory sensation and pain symptoms such as numbness (loss of sensation), tingling, paresthesia (a skin sensation, such as burning, prickling, itching, or tingling, with no apparent physical cause), burning, shooting pain, stabbing or lancinating (characterized by a sensation of cutting, piercing, or stabbing) pain
* Participants having painful diabetic neuropathy in the lower limbs for 3 months before randomization
* Participants diagnosed with Type ll diabetes and stable blood sugar level controlled with an oral medication, insulin or diet therapy for 3 months before randomization
* Participants with glycated hemoglobin (HbA1c) less than or equal to 10 percent
* Participants with pain intensity score of greater than or equal to 4 on numeric rating scale (NRS) for the last 48 hours

Exclusion Criteria:

* Participants who have previously experienced failure of tramadol treatment or have discontinued tramadol administration due to adverse event
* Participants who have received the prohibited medication before 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)
* Participants with neuropathic pain caused by other reasons (e.g., alcohol abuse, connective tissue disease, toxic exposure, infection, neoplasm, ischemia)
* Participants suffering from painful diabetic neuropathy over 10 years
* Participants with physical damage or disease which may cause abnormal absorption, excessive accumulation, metabolism or excretion disorder of the study medication