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Antinociceptive efficacy of parecoxib vs morphine in the PIFIR model

Abstract:

An experimental study was carried out to compare the effectiveness and antinociceptive potential of parecoxib vs IV morphine in the PIFIR model. Experiments were carried out in female Wistar rats, using the PIFIR model. Under anesthesia, the caudal artery was canulated, uric acid was applied intraarticularly in the right hind leg, and electrodes were placed in both hind legs. Rats then walked on rotating cylinders, measuring contact of each leg with the cylinder during a two-minute span. Data were obtained every 30 minutes for 4 hours. These are expressed as functionality index (FI%), with zero meaning established arthritic pain. The study involved the administration of parecoxib or IV morphine, eight different doses, n = 6 for each dose, to a total 108 rats. Results showed a dose-dependent relation for both drugs. As for antinociceptive effectiveness, parecoxib was equivalent to morphine. Regarding the appearance of the effect in time, maximal effect began 0.5 h after administration; both parecoxib and morphine were comparable in terms of time until the effect and magnitude of antinociception. As for antinociceptive effectiveness, there were different "relative potencies", depending on the comparison point. At DE33, parecoxib was 3.7 times more potent than morphine. Under experimental conditions, parecoxib was as effective an analgesic as morphine, which demonstrates the analgesic usefulness of the former. The most important differences were in potency profiles, depending on the point of comparison for pharmacological potency.