Pharmacokinetic parameters for theophylline and dyphylline were evaluated in horse cerebrospinal fluid (csf) and plasma. Pharmacokinetic parameters did not differ significantly (p > 0.05) at the same dose for either drug when administered alone or concomitantly. Theophylline and dyphylline penetrate horse csf to produce approximately 1/2 the concentrations found in plasma. Doubling the theophylline dose from 10 mg/Kg to 20 mg/Kg doubled both csf and plasma theophylline concentrations. However, doubling the dyphylline dose from 20 mg/Kg to 40 mg/Kg tripled both csf and plasma dyphylline concentrations. Simultaneous fitting between plasma and csf drug concentrations indicates that plasma is a good indicator for predicting csf concentrations for both theophylline and dyphylline. The influence of ibuprofen input rate on antipyresis was studied in rats with yeast induced fever. In addition, a data analysis comparison was made between rat data collected from this present study and literature data from fevered children. Counterclockwise hysteresis curves (ibuprofen plasma concentration versus temperature decrement) were observed following ibuprofen oral suspension when administered to rats and children. When the collapsed hysteresis curves were plotted (mean predicted total ibuprofen effect compartment concentration versus mean predicted temperature decrement effect) the rat and children's curves were not superimposable. However, the collapsed hysteresis curves of mean predicted ibuprofen unbound effect concentration versus mean predicted temperature decrement effect were superimposable for data from the rats and children. Based on mean unbound ibuprofen effect compartment concentration versus mean predicted temperature decrement effect, the antipyretic response to ibuprofen appears to be comparable between rats and children. The apparent qualitative trend in temperature decrement, although not statistically significant, perhaps due to variability, appears to be different among ibuprofen input regimens in rats. Maximum temperature decrement appears to relate not just to the concentration of ibuprofen obtained at steady-state, but the rate at which it is obtained. / Graduation date: 1993