Nimodipine is more effective than nifedipine in attenuating morphine tolerance on chronic co-administration in the rat tail-flick test.
Opioids, when co-administered with L-type calcium channel blockers (L-CCBs) show morphine like higher antinociceptive effect. This antinociceptive effect has been further investigated using a different experimental paradigm. The effect of two different L-CCBs (nifedipine and nimodipine) on morphine-induced antinociception was studied by the tail-flick test (40 min after morphine administration) in adult Wistar rats. A fixed-dose of nimodipine or nifedipine (2 mg/kg, once daily) was combined with a fixed dose of morphine (10 mg/kg, twice daily) for 10 days. Co-administration of L-CCBs significantly increased the antinociceptive effect of morphine, even 12 hr after administration. Also, nimodipine was more effective than nifedipine. Nimodipine was further studied using a higher and escalating doses of morphine (20-30 mg/kg twice daily for 14 days). Nimodipine increased the antinociceptive effect of morphine in the latter part of the study (days nine to fourteen) though significant difference was observed on 11th evening and 12th morning. No obvious adverse effects were observed in the present study. The results show for the first time that nimodipine is more effective than nifedipine and that these L-CCBs continue to be effective, even 12 hr after administration in the tail-flick test.
Department of Anatomy, All India Institute of Medical Sciences, New Delhi 110 029, India. sbr_aiims@hotmail.com
Subrata Basu
SB
Ray
Pravash
P
Mishra
Dilip
D
Verma
Ankur
A
Gupta
Shashi
S
Wadhwa
D000701:Analgesics, Opioid / Q000008:administration & dosage / Q000494:pharmacology / Q000627:therapeutic use; D000818:Animals; D001522:Behavior, Animal / Q000187:drug effects; D002121:Calcium Channel Blockers / Q000008:administration & dosage / Q000494:pharmacology*; D004195:Disease Models, Animal; D004305:Dose-Response Relationship, Drug; D004359:Drug Therapy, Combination; D004361:Drug Tolerance; D008297:Male; D009020:Morphine / Q000008:administration & dosage / Q000494:pharmacology / Q000627:therapeutic use; D009543:Nifedipine / Q000008:administration & dosage / Q000494:pharmacology*; D009553:Nimodipine / Q000008:administration & dosage / Q000494:pharmacology*; D010146:Pain / Q000188:drug therapy*; D010147:Pain Measurement; D017288:Pain Threshold / Q000187:drug effects; D051381:Rats; D017208:Rats, Wistar; D012149:Restraint, Physical
D000701:Analgesics, Opioid; D002121:Calcium Channel Blockers; D009553:Nimodipine; D009020:Morphine; D009543:Nifedipine