Efficacy and safety of twice-daily tramadol hydrochloride bilayer sustained-release tablets with an immediate release component for postherpetic neuralgia: Results of a Phase III, randomized, double-blind, placebo-controlled, treatment-withdrawal study.

Background: We investigated the efficacy and safety of twice-daily bilayer sustained-release tramadol hydrochloride tablets (35% immediate-release; 65% sustained-release) in patients with postherpetic neuralgia.

Methods: This was a Phase III treatment-withdrawal study with 1-4-week dose-escalation, 1-week fixed-dose, and 4-week randomized, double-blind, placebo-controlled withdrawal periods performed at 43 medical institutions in Japan. Patients aged ≥20 years, ≥3 months after the onset of herpes zoster with localized, persistent pain despite fixed-dose analgesics for ≥2 weeks before enrollment were eligible. Patients started tramadol at 100 mg/day and its dose escalated to a maximum of 400 mg/day to achieve a reduction in their Numeric Rating Scale (NRS) for pain of ≥2 points. Eligible patients were randomized to continue tramadol or switched to placebo for 4 weeks (double-blind period). Patients were withdrawn due to inadequate analgesia (NRS deteriorated on ≥2 consecutive days) or their request.

Results: Overall, 252 patients started tramadol and 173 were randomized (tramadol: 85; placebo: 88). Tramadol was superior to placebo for the primary endpoint (time from randomization to an inadequate analgesic effect) with log-rank test p = 0.0005. The hazard ratio was 0.353 (95% confidence interval 0.190-0.657) in favor of tramadol and fewer patients in the tramadol group experienced inadequate analgesic effects (16.9% vs. 39.8%). Adverse events in ≥10% of patients in the open-label period were constipation (43.8%), nausea (34.9%), somnolence (18.5%), and dizziness (11.6%). The frequencies of adverse events in the double-blind period were similar in both groups.

Conclusion: Sustained-release tramadol tablets with an immediate-release component are effective and well tolerated for managing postherpetic neuralgia.