Study is aimed at evaluating the effects of ketamine and magnesium sulphate on acute nociceptive pain in rats and examination whether magnesium sulfate added to ketamine or morphine-ketamine combination produces higher level of analgesia.

Analgesic activity was assessed by tail-immersion test in male Wistar rats (200–250 g).

Magnesium sulfate (2.5–60 mg/kg, s.c.) and ketamine (2.5-30 mg/kg, i.p.) given alone did not produce any effect on antinociception. However, there is a synergistic interaction between ketamine (2.5, 5 and 10 mg/kg) and magnesium sulfate (5 mg/kg). Both ketamine and magnesium sulfate, as well as their combination potentiated the antinociceptive effect of morphine (2.6 mg/kg, i.p.).

This study revealed potentiation of ketamine and morphine-ketamine combination by magnesium sulphate in tail-immersion test in rats with higher activity when ketamine is given before magnesium sulfate. It is first time to demonstrate the synergistic interaction between magnesium sulphate and ketamine in lowering body temperature and in antinociception with statistical confirmation.

The authors have not supplied their declaration of competing interest.