title: Reduction in halothane MAC: comparison of morphine and alfentanil.
abstract: The anesthetic potency and effectiveness of alfentanil and morphine were established by determining the effects of increasing drug doses on the alveolar anesthetic requirement of halothane to maintain a constant anesthetic (MAC) level. Six selected doses of alfentanil and four of morphine were administered to groups of mechanically ventilated rats anesthetized with halothane. Alfentanil was given as a loading dose followed by an intravenous infusion of 0.01-100 micrograms X kg-1 X min-1, and morphine was administered as a subcutaneous dose of 4-20 mg/kg. The reduction in halothane requirement after morphine was biphasic, with a rapid linear increase occurring up to an 8 mg/kg subcutaneous dose, followed by a further, slower reduction in halothane requirement after doses of 8-20 mg/kg. At a 20 mg/kg dose, the halothane MAC was reduced approximately 84%. With alfentanil, a curvilinear reduction in halothane MAC occurred up to an alfentanil dose of 15 micrograms X kg-1 X min-1, where a 48% reduction was found. Larger doses produced severe truncal, chest wall, and abdominal rigidity, precluding adequate ventilation and the determination of MAC.
mesh_terms: D000759:Adjuvants, Anesthesia; D015760:Alfentanil; D000818:Animals; D004305:Dose-Response Relationship, Drug; D005283:Fentanyl / Q000008:administration & dosage / Q000031:analogs & derivatives* / Q000097:blood; D006221:Halothane / Q000008:administration & dosage*; D007263:Infusions, Parenteral; D007275:Injections, Intravenous; D007279:Injections, Subcutaneous; D008297:Male; D009020:Morphine / Q000008:administration & dosage / Q000097:blood; D051381:Rats; D011919:Rats, Inbred Strains
chemical_list: D000759:Adjuvants, Anesthesia; D015760:Alfentanil; D009020:Morphine; D005283:Fentanyl; D006221:Halothane