<p>The chemotherapeutics, sulfadiazine (SDA) and trimethoprim (TMP), are extensively used in a variety of animal species. In this study, a pharmacokinetic analysis was performed to compare the bioequivalence of a combined SDA and TMP product against existing licensed SDA and TMP formulations in broiler chickens. Three groups of 15 birds were administered a single dose of either the test formulation or a reference oral suspension. The plasma concentration of SDA and TMP were determined by reverse-phase high performance liquid chromatography (HPLC), and the maximal plasma concentration (C_max), area under the curve (AUC), the peak time (T_max), mean residence time (MRT) and elimination half-life (T_1/2), were calculated for SDA. The combined formulation I and II reference suspension exhibited almost identical concentration-time curves, and ANOVA analyses of the pharmacokinetic parameters identified no significant differences between the reference preparations and the test one. Furthermore the AUC and C_max values of the SDA active ingredient were not significantly different. The I formulation was bioequivalent with both II and III (80-125% and 70–143%, respectively, at the 90% confidence interval). In conclusion, the combined SDA and TMP product was bioequivalent with both existing commercially available SDA suspensions and can be used interchangeably in veterinary medical practice.</p>