title: Prevention of apomorphine- or cisplatin-induced emesis in the dog by a combination of methylnaltrexone and morphine.
abstract: OBJECTIVE
  Morphine can have either an emetic or an antiemetic effect. The emetic effect of morphine can be blocked by methylnaltrexone (MNTX), a quaternary opioid antagonist with peripheral action. In this study, we tested the hypothesis that administering MNTX to block the peripheral emetic effect of morphine would unmask the central antiemetic effect of the morphine. The net result, we hypothesized, would be a reduction in apomorphine- or cisplatin-induced emesis.
  
  
  METHODS
  MNTX 0.25 mg/kg and morphine 1 mg/kg were administered to conscious dogs which were then challenged with the potent emetic agents apomorphine or cisplatin. Emesis was assessed by the presence of characteristic retching motions accompanied by the regurgitation of gastric contents.
  
  
  RESULTS
  We observed that apomorphine challenges of 0.1 mg/kg and of 0.03 mg/kg produced 100% emesis in control animals. After pretreatment with MNTX and morphine, the frequency of emesis with the larger dose of apomorphine was reduced to 50% and with the smaller dose to 22%. MNTX alone did not block apomorphine-induced emesis. In animals challenged with cisplatin 3 mg/kg, the emetic response was 100%. Emesis did not occur in animals pretreated with MNTX 0.25 mg/kg and morphine 1 mg/kg before cisplatin.
  
  
  CONCLUSIONS
  Our results demonstrate that MNTX combined with morphine reduces apomorphine-induced emesis and blocks cisplatin-induced emesis. These results support the hypothesis that the emetic effect of morphine is peripheral and its antiemetic action is central. In combination, MNTX and morphine may have a clinical role in the treatment of chemotherapy-induced emesis.
authors.affiliation: Committee on Clinical Pharmacology, The University of Chicago, IL 60637, USA.
authors.forename: J F
authors.initials: JF
authors.lastname: Foss
authors.forename: C S
authors.initials: CS
authors.lastname: Yuan
authors.forename: M F
authors.initials: MF
authors.lastname: Roizen
authors.forename: L I
authors.initials: LI
authors.lastname: Goldberg
mesh_terms: D000284:Administration, Oral; D000818:Animals; D000932:Antiemetics / Q000008:administration & dosage / Q000627:therapeutic use*; D000970:Antineoplastic Agents; D001058:Apomorphine; D002945:Cisplatin; D004285:Dogs; D004347:Drug Interactions; D004359:Drug Therapy, Combination; D004639:Emetics; D008297:Male; D009020:Morphine / Q000008:administration & dosage / Q000627:therapeutic use*; D009271:Naltrexone / Q000008:administration & dosage / Q000031:analogs & derivatives* / Q000627:therapeutic use; D009294:Narcotics / Q000008:administration & dosage / Q000627:therapeutic use*; D000644:Quaternary Ammonium Compounds; D014839:Vomiting / Q000139:chemically induced / Q000517:prevention & control*
chemical_list: D000932:Antiemetics; D000970:Antineoplastic Agents; D004639:Emetics; D009294:Narcotics; D000644:Quaternary Ammonium Compounds; C032257:methylnaltrexone; D009271:Naltrexone; D009020:Morphine; D001058:Apomorphine; D002945:Cisplatin