Randomized controlled trial of the combined monoaminergic and opioid investigational compound GRT9906 in painful polyneuropathy.

GRT9906 is an investigational novel compound with μ-opioid receptor agonism and inhibition of noradrenalin/serotonin re-uptake. In this randomized, double-blind, placebo-controlled, three-way cross-over trial in painful polyneuropathy, the efficacy and safety of GRT9906 was assessed and compared with tramadol. During 4-week treatment periods, daily oral doses of either GRT9906 120-240 mg, or placebo, or tramadol 200-400 mg were given. These were separated by 1-week washout periods. The primary endpoint was the average pain intensity (average of daily current pain intensity over the last 3 days of each treatment period rated on a 0 to 10-point numeric rating scale). One hundred seventeen patients were enrolled and 64 were randomized to one of six treatment sequences. Forty-seven patients qualified for the per protocol analysis. GRT9906 reduced average pain intensity by 2.1 points compared with a reduction of 0.6 points on placebo (p < 0.0001) and 2.4 points on tramadol. GRT9906 also improved scores on the sleep problem scale and the neuropathic pain symptom inventory and scored better than placebo on the patient global impression of change. Numbers needed to treat to obtain one patient with more than 50% pain relief was 3.9 (95% CI 2.4-11.5) for both GRT9906 and tramadol. The most frequently reported adverse events were nausea, fatigue, constipation and sleep disorder for GRT9906 and tramadol. Four patients dropped out due to adverse events during both GRT9906 and tramadol treatment and two dropped out during placebo treatment. In conclusion, in painful polyneuropathy, GRT9906 demonstrated analgesic efficacy with a magnitude of effect comparable with tramadol and was well tolerated.