Which of the following agents is used for the treatment of post operative shivering?

Treatment of post operative shivering involves oxygen administration to prevent hypoxia, active warming and use of drugs. Pethidine at a minimum dose of 0.35mg/kg is the most effective opioid in the treatment of post anaesthetic shivering. Fentanyl, Aalfentanil and Doxapram at a dose of 0.2mg/kg is also effective. Ref: Textbook of Anesthesia for Postgraduates By T. K. Agasti, Page 387; Fundamentals of Anaesthesia By Ted Lin, 2nd Edition, Pages 70-71.