Hussain, Tanveer, et al. “A COMPARISON OF EQUIPOTENT DOSES OF TRAMADOL AND NALBUPHINE IN GYNECOLOGICAL LAPAROTOMIES POSTOPERATIVELY: Tramadol And Nalbuphine in Gynecological Laparotomies”. Pakistan Armed Forces Medical Journal, vol. 66, no. 5, Oct. 2016, pp. 738-41, https://pafmj.org/PAFMJ/article/view/847.