The use of laxatives is crucial in the treatment of horses with caecal or large colon impaction.To reach the large intestinal contents and resolve the impaction, laxatives must leave the stomach and pass through the small intestine.The aim of this study was to prove whether isotonic solutions of saline cathartics do not affect gastric emptying rate in contrast to hypertonic solutions. Six, fasted, healthy, adult Warmblood horses were used in a randomized study design with 1.8% sodium sulfate (1.8% Na2SO4), 4.2% magnesium sulfate (4.2% MgSO4), 25% sodium sulfate (25% Na2SO4), 25% magnesium sulfate (25% MgSO4) and water at either 20 ml/kg BW (Water 20) or 4 ml/kg BW (Water 4), administered via nasogastric intubation. For indirect measurement of liquid-phase gastric emptying, the liquid-phase passage marker acetaminophen (20 mg/kg BW in 200 ml water) was added to each trial. Serum samples were collected at predetermined time points for pharmacokinetic analysis. The time to reach maximum serum concentration (Tmax) was considered as gastric emptying rate. Compared to Water 4, Tmax of 25% Na2SO4 and 25% MgSO4 was reached significantly later, the maximum serum concentration (Cmax) of acetaminophen was significantly lower and the area under the curve determined up to 90 min (AUC90) was significantly smaller. Isotonic solutions of saline cathartics (1.8% Na2SO4, 4.2% MgSO4) did not influence the gastric emptying rate. Hypertonic solutions of saline cathartics (25% Na2SO4, 25% MgSO4) significantly delayed the gastric emptying rate.