Effect of Duloxetine and Venlafaxine on the Pharmacokinetics and Pharmacodynamics of Oral Tramadol: A Three-phase Randomized Balanced Cross-over Study in Healthy Volunteers

Tramadol is an opioid analgesic, which is widely used in the treatment of acute and neuropathic pain. After oral administration, tramadol is rapidly and almost completely absorbed. Tramadol is extensively metabolised by O- and N-demethylation, which are catalysed by the liver CYP-450 enzymes. O-desmethyltramadol is an active metabolite and its formation is catalysed by CYP2D6. This study is aimed to investigate the possible interaction of oral tramadol with duloxetine and venlafaxine. Duloxetine is known to inhibit CYP2D6. Twelve healthy male or female adult non-smoking volunteers aged 18-40 years with body weights within ±15% of the ideal weight for height are taken into the study. Primary endpoints of the study are plasma concentrations of tramadol and its metabolites.

Inclusion Criteria:

• Healthy volunteers
• Age 18-40
• Body weight within ±15% of the ideal weight for height

Exclusion Criteria:

• A previous history of intolerance to the study drugs or to related compounds and additives
• Concomitant drug therapy of any kind for at least 14 days prior to the study
• Existing or recent significant disease
• History of hematological, endocrine, metabolic or gastrointestinal disease, including gut motility disorders
• History of asthma or any kind of drug allergy
• Previous or present alcoholism, drug abuse, psychological or other emotional problems that are likely to invalidate informed consent, or limit the ability of the subject to comply with the protocol requirements
• A positive test result for urine toxicology
• A "yes" answer to any one of the Abuse Questions
• Pregnancy or nursing
• Donation of blood for 4 weeks prior and during the study
• Special diet or life style conditions which would compromise the conditions of the study or interpretation of the results
• Participation in any other studies involving investigational or marketed drug products concomitantly or within one month prior to the entry into this study
• Smoking for one month before the start of the study and during the whole study period
• Any history of coagulation abnormality, also in first degree relatives