Gadani, H. N., N. B. Patel, and S. C. Gupta. “Role of Butorphanol in Preemptive Analgesia: A Comparison With Pentazocine”. Anaesthesia, Pain & Intensive Care, Jan. 2019, pp. 44-51, https://apicareonline.com/index.php/APIC/article/view/157.