title: Morphine, clonidine coadministration in subanalgesic doses: effective control of tonic pain.
abstract: The aim of the present study was to investigate whether clonidine and morphine interact positively to produce analgesia against the low intensity tonic pain represented by the formalin model in rats. Sub-threshold doses of morphine (0.5 mg kg-1) and clonidine (0.025 mg kg-1) were found to elicit marked antinociceptive effects when co-administered intraperitoneally, 15 min prior to formalin challenge. Repeated administration of this combination for eight days did not exhibit any significant decay of this analgesic response, whilst morphine (2 mg kg-1)-induced analgesia, deteriorated after similar administration. Clonidine and morphine thus exhibit a supra-additive effect against low intensity pain with negligible potential for induction of tolerance. This finding may be relevant for the long term control of chronic pain in certain clinical conditions.
authors.affiliation: Department of Pharmacology and Therapeutics, King George's Medical College, Lucknow, India.
authors.forename: S
authors.initials: S
authors.lastname: Gurtu
authors.forename: S
authors.initials: S
authors.lastname: Shukla
authors.forename: D
authors.initials: D
authors.lastname: Mukerjee
mesh_terms: D000818:Animals; D003000:Clonidine / Q000627:therapeutic use*; D004305:Dose-Response Relationship, Drug; D004357:Drug Synergism; D005260:Female; D005557:Formaldehyde; D007274:Injections, Intraperitoneal; D008297:Male; D009020:Morphine / Q000627:therapeutic use*; D010146:Pain / Q000139:chemically induced / Q000188:drug therapy*; D010147:Pain Measurement / Q000187:drug effects; D051381:Rats; D017208:Rats, Wistar
chemical_list: D005557:Formaldehyde; D009020:Morphine; D003000:Clonidine