Abstract
Background: Evidence has accumulated for the involvement of calcium ions in nociception and N-type voltage-dependent calcium channels being critical for pain transduction and modulation. N-type calcium channel blockers represent a new class of analgesics that are selective for calcium channels involved in pain signal transmission. Gentamicin, an aminoglycoside antibiotic was discovered to block these N-type voltage-dependent calcium channels.

Aims and Objectives: The present study is to evaluate the analgesic activity of gentamicin in thermally induced pain models of rats and mice and compare it against the standard analgesic aspirin.

Materials and methods: A total of 24 rats and 24 mice were distributed into four groups of 6 each: Group A received distilled water as control, Group B received Gentamicin- low dose (80 μg/kg), Group C received Gentamicin- high dose (160 μg/kg), and Group D received standard drug Aspirin (20 mg/kg in rats and 25 mg/kg in mice); all drugs were given intraperitoneally. Analgesic activity was determined using tail flick method and hot plate method. In both the methods, the mean reaction time (MRT) in seconds at 0, 30, 60, 90, and 120 min among the four groups were noted in both rats and mice. The percentage increase in MRT was calculated which indicates the degree of analgesia produced.

Results: In the tail flick test, increase in the MRT was statistically significant (P < 0.05) in Group B, Groups C and D at all the time intervals except 0 min in rats, whereas in mice, it was highly significant (P < 0.001) in only Groups C and D. In hot plate method, in rats, the increase in MRT was statistically significant (P < 0.05) at 90 and 120 min in Group C and at 60 min in Group D, whereas it was highly significant at 90 min in Group D. In mice, increase in MRT was found to be significant at 90 min in Group B, at 60 and 120 min in Group C and at 120 min in group D whereas it was highly significant at 90 min in Group C and at 60 and 90 min in Group D.

Conclusion: Gentamicin showed a comparable analgesic activity to aspirin in tail flick method but lower analgesic activity in hot plate method in both rats and mice.

Key words: Hot Plate Method; Mean Reaction Time; N-type Calcium Channels; Tail Flick Method