Objective To evaluate the efficacy of clemastine fumarate in antagonizing atracuriuminduced release of histamine in the patients undergoing surgery under general anesthesia.Methods Eighty American Society of Anesthesiologists physical status Ⅰ or Ⅱ patients,aged 21-59 yr,with body mass index of 17-26 kg/m2,scheduled for elective modified radical mastectomy,were divided into 2 groups (n=40 each) using a random number table:control group (group C) and clemastine fumarat group (group CF).Clemastine fumarate 2 mg was injected intramuscularly at 20 min before induction of anesthesia.Anesthesia was induced with iv midazolam 0.1 mg/kg,etomidate 0.3 mg/kg,fentanyl 4-6 μg/kg and atracurium 0.8 mg/kg.The patients were mechanically ventilated after insertion of the larygeal mask airway.Anesthesia was maintained with inhalation of 2％ sevoflurane.Before administration of clemastine fumarate,at 20 min after administration,immediately before administration of atracurium,and at 2,5,10 and 20 min after administration of atracurium,arterial blood samples were taken for determination of plasma histamine concentrations,and the peak airway pressure and degree of cutaneous color were recorded.The development of histaminemia and adverse cardiovascular events was assessed.Steward recovery scores and Ramsay sedation scores were recorded at 10 min after removal of the laryngeal mask airway.Results The incidence of histaminemia was 60％ and 8％ in C and CF groups,respectively.Compared with group C,the plasma histamine concentrations,incidence of histaminemia,degree of cutaneous color,and incidence of hypotension and tachycardia were significantly decreased (P＜0.05),and no significant change was found in the peak airway pressure,Steward recovery scores and Ramsay sedation scores in group CF (P＞0.05).Conclusion For atracurium-induced release of histamine in the patients undergoing surgery under general anesthesia,clemastine fumarate 2 mg injected intramuscularly before operation can not only antagonize histamine at H1 level,but also reduce histamine release,and exerts no influence on recovery from anesthesia and produces good antihistamine efficacy.