One hundred fifty patients with maxillofacial skeletal trauma that need open reduction and internal fixation were randomly assigned to receive one of the following drugs orally , 1 hour preoperative : 10 mg metoclopramide ( group A ) , 300 mg gabapentin ( group B ) , 100 mg chlorpromazine ( group C ) , 5 mg dexamethasone ( group D ) , and placebo ( group E ) .