Rana, R. B., Z. Rahman, L. Aziz, A. Akhtaruzzaman, and K. M. Iqbal. “A Study on Epidural Tramadol Compared With Epidural Fentanyl Combined With Low Dose Bupivacaine for the Control of Metastatic Cancer Pain”. Bangabandhu Sheikh Mujib Medical University Journal, vol. 2, no. 2, Apr. 2010, pp. 66-72, doi:10.3329/bsmmuj.v2i2.4760.