Background: Tramadol, an analgesic, is a prodrug requiring bioactivation through cytochrome P450 enzymes (CYP450) to obtain O-desmethyltramadol (M1), its active metabolite. However, little is known on the African pharmacogenetic profile of tramadol metabolism. Hence, we aimed to study the biological efficacy of tramadol in an African population.Methods: This was a prospective cohort study over a 3-month period carried out at intensive care unit of a Cameroonian tertiary hospital. We enrolled patients with moderate-to-severe pain surgery, who had not been administered drugs metabolized by CYP450. Immediately after surgery, 2 mg/kg of tramadol was administered intravenously every 6 hours. Pain was assessed using the visual analog scale (VAS) within the first 24 hours. Vital signs and side effects were recorded. Plasma samples were collected at 3rd and 6th hours to assay tramadol and M1 using HPLC-UV.Results: We enrolled 30 patients with a mean age of 32 years operated for caesarean section, laparotomy and cancer surgery, under spinal and general anesthesia. Before administration of tramadol, the VAS was 6/10. The VAS decreased 4/10 to 1/10 between the 3rdand the 6th hour. There was a reduction of the respiratory rate of 3 breath cycles per minute as early as the 6th hour. Samples from 13 patients were analyzed. M1 was found in all patients; of which 4 had a slow metabolism and 3 had a faster metabolism.Conclusions: Overall there was good correlation between the clinical and biological analgesic efficacy of tramadol.