A Study to Assess the Safety and Efficacy of 7 Days Treatment With a Novel Analgesic in Subjects With Peripheral Neuropathic Pain

Inclusion Criteria:

• Age 18 years to 75 years
• Presence of of persistent neuropathic pain for at least 6 months at the time of the Enrollment Visit. Allowed reasons for neuropathic pain are: modified radical mastectomy, breast conserving surgery, or cosmetic breast surgery. [Germany: subjects after cosmetic breast surgery may not be enrolled.]
• Presence of "probable" or "definite" neuropathic pain.
• Presence of dynamic mechanical allodynia on the affected side, or alternatively, the mechanical pain sensitivity for any of the pinprick stimuli is higher on the affected compared to the contralateral side.
• At either Visit 5 or Visit 6: Presence of an average evoked pain intensity score of >20 on the 0 100 point numeric rating scale (NRS) for at least 1 of the 3 clinical sub-tests for dynamic mechanical allodynia (i.e., standardized brush, cotton wool tip or cotton wisp). The average will be calculated as the arithmetic mean of all measurements per sub test. Alternatively, the arithmetic mean of the 5 test replicates for any of the pinprick stimuli for mechanical pain sensitivity is at least 3 times higher for the affected side compared to the contralateral side.
• Presence of an average ongoing pain intensity score of >4 to <9 on the 0-10 point numerical rating scale (NRS) without the use of rescue medication within the 3 day Baseline pain intensity evaluation Period with at least 7 of 9 assessments being present.
• Dissatisfaction with the current treatment (i.e., lack of efficacy or intolerable side effects) if taking an opioid or non opioid analgesic medication for the painful neuropathy before enrollment.

Exclusion Criteria:

• Any kind of hepatic impairment at Visit 1 or at Visit 3.
• Either active hepatitis within the past 3 months or presence of chronic hepatitis irrespective of its activity status.
• Estimated creatinine clearance of less than 60 mL/minute x 1.73 m2 at either Visit 1 or at Visit 3.
• Clinically relevant cardiac disease (e.g., unstable angina pectoris, angina pectoris Canadian Cardiovascular Society [CCS] Grade III to IV, acute myocardial infarction within the last 3 months, cardiac insufficiency New York Heart Association [NYHA] Class III to IV).

• Electrocardiogram (ECG) with clinically relevant findings at either Visit

  1 or at Visit 3, including but not limited to repeated prolongation of QTc > 450 ms (Fridericia correction), or a history of additional risk factors for torsade de pointes (e.g., family history of Long QT Syndrome).

• Clinically relevant pulmonary disease (e.g., Medical Research Council breathlessness scale of 2 or above).
• Specific antitumor therapy within the last 6 months, e.g., adjuvant radiotherapy or chemotherapy, biologics, or angiogenesis inhibitors.
• CYP2D6 poor metabolizer phenotype as predicted by CYP2D6 genotyping.
• Presence of confounding pain conditions (e.g., ulnar nerve entrapment, radial nerve injury associated with major soft-tissue or bone damage, cervico-thoracic radiculopathy, carpal tunnel syndrome, chemotherapy-induced peripheral neuropathy, or complex regional pain syndrome type I or type II).
• Phantom breast or phantom limb pain.
• Presence of exclusively negative symptoms of neuropathic pain (e.g., hypoesthesia or total anesthesia) in the affected area.