Tulathromycin use in healthy adult horses

Tulathromycin, a macrolide antibiotic, has been used in food animal medicine for a time and is a readily available, economical antibiotic. Here is a look at using the product in horses. Intramuscular and subcutaneous use was dependably associated with adverse effects so cannot be recommended. On the other hand, slow IV administration was well tolerated and able to achieve what should be adequate plasma concentrations for the treatment of susceptible pathogens, mainly gram-positive bacteria. Of interest is the long plasma half-life which may make infrequent administration possible. Before recommending use these promising findings need to be investigated in greater detail and for longer periods.
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Pharmacokinetics and pulmonary distribution of Draxxin ® (tulathromycin) in healthy adult horses
J Vet Pharmacol Ther. 2021 Mar 14. doi: 10.1111/jvp.12968. Online ahead of print.
Authors
Hannah R Leventhal 1 , Harold C McKenzie 1 , Krista Estell 2 , McAlister Council-Troche 3 , Jennifer L Davis 3
Affiliations

1 Department of Large Animal Clinical Sciences, Virginia-Maryland College of Veterinary Medicine, Blacksburg, VA, USA.
2 Marion duPont Scott Equine Medical Center, Virginia-Maryland College of Veterinary Medicine, Leesburg, VA, USA.
3 Department of Biomedical Sciences and Pathobiology, Virginia-Maryland College of Veterinary Medicine, Blacksburg, VA, USA.

PMID: 33719056
DOI: 10.1111/jvp.12968

Abstract

The objective of this study was to determine the pharmacokinetics and tolerability of tulathromycin (Draxxin® ; 2.5 mg/kg once) after intramuscular (IM), subcutaneous (SC), and slow intravenous (IV) administration to six adult horses. A three-phase design and 4-week washout period were used. Drug concentrations in blood and bronchoalveolar lavage (BAL) samples were determined by ultra-performance liquid chromatography tandem mass spectrometry and pharmacokinetic parameters calculated using noncompartmental analysis. Following SC and IM administration, all horses exhibited sweating, discomfort, and periods of recumbency. As signs were more severe after SC administration this route was only used in 3/6 horses. Intravenous administration of tulathromycin was well tolerated in all horses. Mean bioavailability was 99.4% IM and 115% SC. Mean maximum plasma concentration was 645 ng/ml IM and 373 ng/ml SC. Mean half-life was 59.8 h, 54.8 h, and 57.9 h for IV, IM, and SC administration, respectively. Mean clearance was 3.25 ml/kg/min, and mean volume of distribution was 16.8 L/kg following IV administration. Drug was detectable in plasma and BAL samples for 120 h following all routes; however, adverse effects may prevent IM use and SC use is not recommended. Tulathromycin may be a practical and affordable antimicrobial for use in adult equine patients.

Keywords: adverse drug reaction; antibiotic; equine; macrolides.