The inhibition of nociceptive stimuli of pethidine was studied in relation to the concentration of the drug in blood and brain tissue, in 9 to 11-day and in 18-month-old rats. Pethidine was administered subcutaneously and intraperitoneally in a dose of 20 mg/kg.
It has been found that the inhibition of nociceptive stimuli of pethidine after administration of equal doses is significantly higher in 18-month-old animals as compared to 9 to 11-day-old rats. However, in aged animals concentrations of pethidine in blood and brain were significantly lower, in comparison with young rats.