Time course of the antihyperalgesic effects of CEF + IBU (A), CEF + CEL (B), CEF + PAR (C), and CEF + LEV (D) combinations. Basal df (plotted at vertical axis) was obtained before drugs administration and the induction of inflammation by an i.pl. injection of CAR. CEF was administered i.p. once daily for 7 days before induction of inflammation. IBU and CEL were administered p.o. immediately after CAR, whereas LEV and PAR were administered p.o. 60 min after CAR (denoted by arrows). Drugs were administered at fixed-dose fractions of their respective ED₅₀ (1/16 = 0.0625, 1/8 = 0.125, 1/4 = 0.25, and 1/2 = 0.5). Each point represents the mean ± SEM. **P < 0.01 compared with control group at each time point (Tukey honestly significant difference post hoc test after two-way repeated-measures ANOVA). CAR = carrageenan; CEF = ceftriaxone; CEL = celecoxib; df = paw pressure difference between noninjected and CAR-injected rat hind paw; ED₅₀ = effective dose that produces 50% of the antihyperalgesic effect; IBU = ibuprofen; i.p. = intraperitoneal; i.pl. = intraplantar; LEV = levetiracetam; PAR = paracetamol; p.o. = oral.