Effect of tulathromycin on abomasal emptying rate in healthy lactating goats

Abstract

Tulathromycin is a long-acting semi-synthetic macrolide antibiotic that is synthesized from erythromycin. Macrolides have pharmacodynamic properties beyond their antimicrobial effects, including anti-inflammatory and immunomodulatory properties that are perceived to be clinically beneficial. An additional pharmacodynamic property of macrolides is a prokinetic effect, which is marked in adult cattle and calves administered erythromycin and less prominent in calves administered spiramycin, tilmicosin, and tylosin. Based on structural similarities to erythromycin, the hypothesis was that parenteral administration of tulathromycin would increase abomasal emptying rate in healthy adult goats. Accordingly, five adult lactating goats (30–36 months of age) received each of the following 3 treatments: IM injection of 2mL of 0.9% NaCl (control); IM injection of tulathromycin (2.5mg/kg body weight); IV injection of tulathromycin (2.5mg/kg body weight). Abomasal emptying rate was assessed by acetaminophen absorption, which was injected into the abomasum through a surgically placed abomasal cannula at 50mg/kg BW, 15min after each treatment. Jugular venous blood samples were obtained periodically after injection and plasma acetaminophen concentrations determined using a colorimetric nitration assay. The maximum observed plasma acetaminophen concentration (Actual Cmax) and time of actual Cmax (Actual Tmax) were determined, and pharmacokinetic modeling was used to calculate model Cmax and model Tmax and abomasal emptying half-time (T50). Results showed that tulathromycin (IM and IV) increased abomasal emptying rate, as indicated by a shorter time to actual Tmax and model Tmax, and shorter T50, than control. The clinical relevance of these findings remains to be determined.