This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Anaesthesia
Treatment in post operative shivering? 
Select and explain. 
A. Pethidine, B. Piritramide, C. Methadone, D. Pentazocine
A: Pethidine
Answer: A: Pethidine 
Explanation: Ans. is 'a' i.e., Pethidine Post-anaesthesia shivering (PAS) Post anaesthesia (post operative) shivering occurs in 40% of patients recovering from general anaesthesia. Some time it is preceded by central hypothermia and peripheral vasoconstriction, indicating that it is a thermoregulatory mechanism Pethidine is most effective drug for treatment of PAS. Other drugs used are --clonidine, doxapram, ketanserin, alfentonil, butorphanol, chlorpromazine.