Efficacy, Safety, Tolerability and Pharmacokinetics of Concomitant Administration of Tramadol With Duloxetine or Pregabalin

Efficacy, Safety, Tolerability and Pharmacokinetics of Concomitant Administration of Tramadol With Duloxetine or Pregabalin: a Randomized Controlled Flexible-dose Study in Patients With Neuropathic Pain

Tramadol is an opioid analgesic, which is widely used in the treatment of acute and neuropathic pain. Treatment of neuropathic pain often requires a combination of pain medications due to the complex nature of neuropathic pain and frequent inadequate response to drug treatment. Common drugs used concomitantly with tramadol are SNRI antidepressant duloxetine and anticonvulsants such as pregabalin. Both tramadol and duloxetine have serotonergic effects and duloxetine has also a potential to inhibit metabolism of tramadol. The objective of the study is to investigate the pharmacokinetics and pharmacodynamic interaction of oral tramadol with duloxetine and pregabalin in patients with chronic neuropathic pain due to postherpetic neuralgia or diabetic polyneuropathy. All subjects will receive tramadol and duloxetine or tramadol and pregabalin in a randomized double-blind order. Primary end point is O-desmethyltramadol concentration.

Inclusion Criteria:

• Chronic (≥ 6 months) neuropathic pain due to postherpetic neuralgia or diabetic polyneuropathy
• Pain intensity ≥ 4 on a numerical scale of 0-10
• Informed consent

Exclusion Criteria:

• Clinically significant abnormalities in laboratory screening
• Pregnancy
• Depression
• Use of strong opioids (morphine, oxycodone, fentanyl, hydromorphone, methadone)
• A previous history of intolerance or allergy to the study drugs or to related compounds and additives
• Existing or history of seizures, haematological disorders, clinically significant renal, hepatic, respiratory, cardiac or psychiatric disease, dementia, drug allergy
• Previous or present alcoholism, drug abuse, psychological or other emotional problems or cognitive impairment that are likely to invalidate informed consent or limit the ability of the subject to comply with protocol requirements
• Concomitant drug therapy known to cause significant enzyme induction or inhibition of CYP 1A2, 2D6, 3A4, 2B6, drugs metabolised by CYP2D6 enzyme, antidepressants, MAO-inhibitors, non-steroidal anti-inflammatory analgesics.