Chloramphenicol disposition and pharmacokinetics in adult horses

Pulmonary disposition and pharmacokinetics of a single oral dose of chloramphenicol in healthy fasted adult horses

Am J Vet Res. 2025 Feb 6:1-10. doi: 10.2460/ajvr.24.08.0223. Online ahead of print.
Authors
Lana Dedecker 1 , Serena Ceriotti 1 , Mariano Mora-Pereira 1 , Heather K Knych 2 , Emily Zuber 3 , Kara M Lascola 1
Affiliations

1 Department of Clinical Sciences, College of Veterinary Medicine, Auburn University, Auburn, AL.
2 Kenneth L. Maddy Equine Analytical Chemistry Laboratory (Pharmacology), School of Veterinary Medicine, University of California-Davis, Davis, CA.
3 Department of Pathobiology, College of Veterinary Medicine, Auburn University, Auburn, AL.

PMID: 39914007
DOI: 10.2460/ajvr.24.08.0223

Abstract

Objective: To describe and compare the pulmonary and plasma pharmacokinetics of different oral formulations of chloramphenicol administered as a single dose to healthy adult horses.

Methods: A single dose of chloramphenicol was administered to 6 healthy, university-owned fasted adult horses IV (25 mg/kg), orally as commercial tablets (50 mg/kg), or orally or intragastrically as compounded suspension (50 mg/kg), according to a randomized crossover protocol. Plasma was collected 5, 10, 15, 20, and 30 minutes and 1, 1.5, 2, 3, 4, 6, 8, 12, and 24 hours after drug administration. Bronchoalveolar lavage (BAL) fluid was collected after 1, 4, and 8 hours and processed to obtain pulmonary epithelial lining fluid (PELF) and the BAL cell pellet (BALc). Chloramphenicol concentrations were determined by means of liquid chromatography-tandem mass spectrometry in plasma, PELF, and BALc. Data were used for plasma noncompartmental analysis and calculation of apparent PELF and BALc concentrations.

Results: Chloramphenicol concentrations were higher in the PELF than in plasma, irrespective of formulation and administration route (IV, orally, or intragastrically). Compounded suspension administered intragastrically yielded higher maximum concentration and drug exposure than administered orally, with a relative bioavailability of 79%. After oral administration, no significant differences were found between compounded suspension and commercial tablets.

Conclusions: Oral administration of chloramphenicol achieved pulmonary concentrations ≥ 2 and 4 µg/mL for at least 4 hours (50% to 75% of a 6- to 8-hour dosing interval) in 4 out of 5 treated horses.

Clinical relevance: Pulmonary pharmacokinetics can be used by practitioners to judiciously select an antimicrobial for the treatment of complex equine pneumonia cases.

Keywords: antimicrobial; equine; lung; pharmacokinetics; pneumonia.