Objective - To evaluate the effect of parenteral administration of ivermectin and erythromycin on abomasal emptying rate in suckling calves. Animals - 6 male Holstein-Friesian calves < 15 days old. Procedures - In a crossover study, calves were administered each of 3 treatments (control treatment, 2 mL of saline [0.9% NaCl] solution, IM; erythromycin, 8.8 mg/kg, IM; and ivermectin, 200 μg/kg, IV). Thirty minutes later, calves were bottle-fed 2 L of fresh cow's milk containing acetaminophen (50 mg/kg). Blood samples were collected from a jugular vein at various periods after suckling of milk. Abomasal emptying rate was assessed by use of the time to pharmacokinetically determined maximal plasma acetaminophen concentration. Results - Administration of erythromycin and ivermectin caused a significant increase in abomasal emptying rate, compared with results for the control treatment, as determined on the basis of time to maximal plasma acetaminophen concentration. Conclusions and Clinical Rellevance - Parenteral administration of erythromycin and ivermectin increased the abomasal emptying rate. The macrolide erythromycin can be an effective prokinetic agent in calves and other animals. Ivermectin is classified as a macrolide but has a number of structural differences from erythromycin. The clinical importance of a slight increase in abomasal emptying rate after IV administration of ivermectin remains to be determined because ivermectin is only labeled for SC, oral, and topical administration.
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