Objective: This open-label study was performed to evaluate the efficacy and safety of oral treatment with the antioxidant alpha-lipoic acid (ALA, thioctic acid) in Korean diabetic patients with distal symmetric polyneuropathy (DSP).
Subjects and methods: Thioctic acid was administered orally using 600 mg once daily for 8 weeks in 61 diabetic patients with symptomatic polyneuropathy. Neuropathic symptoms (pain, burning sensation, paresthesia, and numbness) were scored at baseline as well as at 4 and 8 weeks following treatment. In addition, neurological assessment was carried out before and after 8 weeks of treatment, and an overall evaluation was performed at the end of treatment. The primary endpoint was the response rate after 8 weeks of treatment, defined as an improvement in the Total Symptom Score (TSS) of > or =30%.
Results: Efficacy was evaluated in 38 patients who had completed the study according to the protocol. Safety was evaluated in all 61 patients who had taken the study medication. Fasting blood glucose and HbA(1)c did not change during the study. The response rate after 8 weeks was 71.4%. At 4 weeks, the response rate was 47.4%. The TSS significantly decreased at 4 weeks, which decreased further at 8 weeks (P<.05). All the individual scores for neuropathic symptoms (pain, burning sensation, paresthesia, and numbness) were also significantly reduced at 4 weeks and further decreased at 8 weeks (P<.05). The duration of diabetes, severity and duration of diabetic polyneuropathy, and all the other demographic and metabolic parameters did not demonstrate an effect on the response rate. The parameters of neurological assessment (ankle reflexes, pin-prick test, 10-g monofilament test) and quantitative sensory tests (vibration, warm and cold sensation) were not influenced by 8 weeks of treatment with 600 mg of oral thioctic acid per day. Overall efficacy rated as "good/fair" was 86.8% by the physician and 76.3% by the patients at the end of an 8-week treatment period. Eleven episodes (18.0%) of adverse events (possibly, probably, definitely related) were reported in seven patients (11.5%).
Conclusion: These findings indicate that oral treatment with thioctic acid at a dose of 600 mg/day for 8 weeks improved symptoms of polyneuropathy in Korean diabetic patients without causing serious adverse events.