Safety and effectiveness of topiramate for the management of painful diabetic peripheral neuropathy in an open-label extension study

Objective: The aim of this study was to further assess the long-term safety and effectiveness of open-label topiramate therapy in subjects with moderately to severely painful diabetic peripheral neuropathy (DPN). Methods: Adults aged 18 to 75 years received open-label topiramate (25-600 mg/d for 26 weeks) in an extension of a previously published randomized, double-blind trial comparing topiramate with placebo. Safety analyses included adverse event (AE) reports and clinical laboratory tests. Metabolic end points included body weight and glycosylated hemoglobin (HbA_1c). Effectiveness analyses included a 100-mm pain visual analog (PVA) scale, worst and current pain severity, and sleep disruption. Results: Two hundred five subjects participated in this open-label extension study (118 formerly treated with topiramate and 87 who formerly received placebo). The groups did not differ in baseline demographics or disease characteristics. One hundred twenty-four (60.5%) subjects (68.6% of former topiramate recipients and 49.4% of former placebo recipients) completed the extension study; the most common reason for discontinuation was an AE (27.3% of subjects). AEs among subjects who received <1 dose of topiramate (n = 298) included upper respiratory tract infection (16.1%), anorexia (15.1%), diarrhea (12.8%), nausea (12.8%), paresthesia (10.7%), and headache (10.1%). Baseline pain scores were lower in those formerly treated with topiramate (n = 117) than in the former placebo group (n = 86) (PVA: 43.3 vs 52.5, P = 0.014; worst pain: 1.9 vs 2.5, P < 0.001; current pain: 1.6 vs 1.9, P = 0.026; sleep disruption: 3.6 vs 4.6, P = 0.021). At the final visit, PVA, current pain, and sleep disruption scores were not significantly different between the former topiramate and former placebo groups, but worst pain differed significantly (1.4 vs 1.8; P = 0.025). Mean weight loss from the start of topiramate therapy was 5.2 and 5.3 kg in the former topiramate and former placebo groups, respectively (P < 0.001 vs baseline). Mean HbA_1c values before and after topiramate treatment were 7.7% and 7.4%, respectively, in the former topiramate group (P = 0.004 vs baseline), and 7.6% and 7.1%, respectively, in the former placebo group (P < 0.001 vs baseline). Conclusion: Although 39.5% of subjects discontinued, most often due to AEs, the results of this 26-week, open-label extension study with topiramate (up to 600 mg/d) in subjects with moderately to severely painful DPN suggest that pain relief was effective and durable.