Objective To evaluate the effect of the expression of P-glycoprotein (P-gp) in the tumor tissue on the analgesic efficacy of fentanyl and lornoxicam in patients with cancer pain. Methods One hundred advanced cancer patients with pain aged 49-64 yr weighing $$-65 kg were included in this study. The expression of Pgp was positive in the tumor tissue in 50 patients (groups F1 and L1, n = 25 each) and negative in 50 patients (groups F2 and L2, n = 25 each). The patients in 4 groups received 48 h of pstient-controlled intravenous analgesia (PCIA). A loading dose of fentanyl 0.05 mg was administered before PCIA was started in groups F1 and F2 .The PCIA solution contained fentanyl 1 mg and droperidol 5 mg in 100 ml of normal saline in groups Ft and F2, or lomoxicam 64 mg and droperidol 5 mg in 100 ml of normal saline in groups L1 and L2. The PCA pump was set to deliver a background infusion of 2 ml/h and a bolus dose of 0.5 ml at 15 min lockout interval. Pain was assessed with VAS scores (0 = no pain, 10 = worst pain), and VAS score was maintained at ≤3 during PCIA. Flurbiprofen 50 mg was injected intravenously when VAS score≥4 and the consumption of flurbiprofen was recorded. The consumption of fentanyl and lornoxicam during PCIA was recorded. Blood samples from the internal jugular vein were taken at the beginning of PCIA (T0), and at 4, 12, 24, 48 h of PCIA (T1-4) for determination of blood fentanyl and lornoxicam concentrations. Results Flurbiprofen was not used in groups F2, L1 and L2. The consumption of flurbiprofen was ( 184 ± 41 ) mg in group F1 . There was no significant difference in the consumption of fentanyl during PCIA between groups F1 and F2 ( P ＞ 0.05). Blood fentanyl concentrations were not detected at all the time points in groups F1 and F2 . The VAS score during PCIA ≤ 3 in groups L1 and L2, and there was no significant difference in blood concentrations of lornoxicam at each time point and the consumption of lornoxicam during PCIA between groups L1 and L2 ( P ＞ 0.05). Conclusion Positive P-gp expression in the tunor tissue can decrease the analgesic efficacy of fentanyl, but exerts no effect on the analgesic efficacy of lornoxicam in patients with cancer pain.