Background: Commonly used dosage protocols for antimicrobial agents may alter the rate of gastric emptying. Hypothesis: Parenteral administration of erythromycin increases and gentamicin decreases the rate of abomasal emptying. Animals: Five male Holstein-Friesian calves (8-15 days of age). Methods: Calves received each of the following 4 IM treatments in random order: control, 2 mL of 0.9% NaCl; erythromycin, 8.8 mg/kg; low-dose gentamicin, 4.4 mg/kg; high-dose gentamicin, 6.6 mg/kg. Abomasal emptying rate was assessed by acetaminophen and glucose absorption. Calves were fed 2 L of cow's milk containing acetaminophen (50 mg/kg body weight) 30 minutes after each treatment was administered, and jugular venous blood samples were obtained periodically after suckling. The maximum observed plasma acetaminophen concentration (actual C max ) and time of actual C max (actual T max ) were determined, and pharmacokinetic modeling was used to calculate model C max and model T max .Results: Erythromycin increased abomasal emptying rate, as indicated by a shorter time to actual T max and model T max (P o .05). Abomasal emptying rate after injection of low-dose gentamicin was similar to that of control. Administration of high-dose gentamicin resulted in a longer time to actual T max (P 5 .021) but did not change model T max (P 5 .62).Conclusions and Clinical Relevance: IM injection of erythromycin increased abomasal emptying rate in dairy calves, whereas low-dose and high-dose gentamicin did not alter the rate of abomasal emptying as measured by acetaminophen kinetics and glucose absorption. The clinical relevance of these findings remains to be determined.
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