The purpose of this study was to determine the effect of concurrent sucralfate (tablet or suspension) on doxycycline pharmacokinetics and to determine the effects of delaying sucralfate by 2 h on doxycycline absorption. Five dogs were included in a crossover study receiving: doxycycline alone; doxycycline concurrently with sucralfate tablet; doxycycline followed 2 h by sucralfate tablet; doxycycline concurrently with sucralfate suspension; and doxycycline followed 2 h by sucralfate suspension. Doxycycline plasma concentrations were evaluated with liquid chromatography with mass spectrometry. No interaction was seen when sucralfate was administered as a tablet. Sucralfate tablet fragments were frequently observed in some dogs' feces. The area under the curve (AUC) and maximum plasma concentration (CMAX) were significantly lower (P < 0.001) in the concurrent sucralfate suspension group (AUC 7.2 h·μg/mL, CMAX 0.43 μg/mL) than with doxycycline alone (AUC 36.0 h·μg/mL, CMAX 2.53 μg/mL) resulting in a relative bioavailability of 20%. Delaying sucralfate suspension by 2 h after doxycycline administration resulted in no difference in doxycycline absorption as compared with doxycycline administration alone with a relative bioavailability of 74%. The lack of an interaction with sucralfate tablets suggests sucralfate should be administered as a suspension rather than tablet in dogs.