Material and Method: A single-blind evaluation randomized controlled trial (RCT) of patients that were diagnosed with low back pain with suspected neuropathic component at the Department of Rehabilitation Medicine, King Chulalongkorn Memorial Hospital were included in the present study. Patients were randomized into two treatment groups. The first group received gabapentin generic form (GGF) or Gabapentin Sandoz, whereas the other received gabapentin original form (GOF) or Neurontin. The primary endpoint was the Visual Analogue Scale (VAS) pain score. The secondary endpoints were the Thai version of the Oswestry low back pain disability index (ODI) score, lumbar spine’s range of motion, safety profiles, and average medical cost. Non-inferiority was pre-specified at 20%. The amount of medication was increased to maintain VAS less than 40 mm and tapered off in case of adverse event.

Results: Forty-one patients, GGF 21 and GOF 20, had completed the study. At 8th week, the visual analogue scale (VAS) and ODI scores significantly decreased in both groups. Mean and standard deviation (SD) of VAS improvement were 31.4±22.1 mm for the GGF group versus 34.3±22.6 mm for the GOF group (p = 0.69), within pre-specified 20% non-inferiority margin (difference 2.9 mm 95% CI -17.7 mm, 11.8 mm). Mean ODI improvement was 11.1% for the GGF group versus 7.6% for the GOF group (p = 0.42), within pre-specified 20% non-inferiority margin, (difference 3.5, 95% CI = -12.3%, 5.3%). Both groups have significantly gained flexion of the lumbar spine. Both groups revealed similar safety profiles. The GGF group showed significantly lower average cost for medications (2,844 baht).

Conclusion: In comparison with the GOF (Neurontin) group, the non-inferior effectiveness for pain reduction and improvement of back function has been revealed in the GGF (Gabapentin Sandoz) group. Similar safety profiles were demonstrated in both groups. The average medication cost of GGF is much lower than GOF (4.67 times).

Keywords: Generic, Gabapentin, Non-inferiority trial, Low back pain, Neuropathic component