Pharmacological interaction between oxcarbazepine and two COX inhibitors in a rat model of inflammatory hyperalgesia

Oxcarbazepine, ibuprofen and etodolac have efficacy in inflammatory pain. The combination of different drugs activates both central and peripheral pain inhibitory pathways to induce additive or synergistic antinociception, and this interaction may allow lower doses of each drug combined and improve the safety profile, with lower side-effects. This study aimed to examine the effects of oxcarbazepine-ibuprofen and oxcarbazepine-etodolac combinations, in a rat model of inflammatory hyperalgesia, and determine the type of interaction between drugs. Rats were intraplantarly injected with carrageenan (0.1 ml, 1%) and the hyperalgesia was assessed by modified paw pressure test. The anti-hyperalgesic effects of oxcarbazepine, ibuprofen and etodolac and oxcarbazepinei-buprofen and oxcarbazepine-etodolac combinations were examined. Drugs were co-administered in a fixed-dose fractions of the ED(50) and the type of interaction was determined by isobolographic analysis. Oxcarbazepine (40-160 mg/kg; p.o.), ibuprofen (10-120 mg/kg; p.o.) and etodolac (5-20 mg/kg; p.o.) produced a significant, dose-dependent anti-hyperalgesia in carrageenan-injected rats. ED(50) values (mean +/- SEM) for oxcarbazepine, ibuprofen and etodolac were 88.17 +/- 3.65, 47.07 +/- 10.27 and 13.05 +/- 1.42 mg/kg, respectively. Oxcarbazepine-ibuprofen and oxcarbazepine-etodolac combinations induced significant and dose-dependent anti-hyperalgesia. lsobolographic analysis revealed that oxcarbazepine exerts a synergistic interaction with ibuprofen, with almost 4-fold reduction of doses of both drugs in combination. In contrast, there was an additive interaction with etodolac. Synergistic interaction of oxcarbazepine with ibuprofen and its additive interaction with etodolac provide new information about the combination pain treatment and could be explored further in patients with inflammatory pain. Adverse effect analysis of the combinations is necessary to verify possible clinical use of the mixtures