Pharmacokinetics of oral chlortetracycline in nonpregnant adult ewes

Authors

  • K. Washburn,

    Corresponding author
    1. Department of Large Animal Clinical Sciences, Texas A&M University, College of Veterinary Medicine and Biomedical Sciences, College Station, TX, USA
    • Kevin Washburn, Department of Veterinary Large Animal Clinical Sciences, College of Veterinary Medicine, MS 4475, College Station, TX 77843, USA. E-mail: kwashburn@cvm.tamu.edu

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  • V. R. Fajt,

    1. Department of Veterinary Physiology and Pharmacology, Texas A&M University, College of Veterinary Medicine and Biomedical Sciences, College Station, TX, USA
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  • P. Plummer,

    1. Department of Veterinary Diagnostic and Production Animal Medicine, Iowa State University, College of Veterinary Medicine, Ames, IA, USA
    2. Department of Veterinary Microbiology and Preventative Medicine, Iowa State University, College of Veterinary Medicine, Ames, IA, USA
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  • J. F. Coetzee,

    1. Department of Veterinary Diagnostic and Production Animal Medicine, Iowa State University, College of Veterinary Medicine, Ames, IA, USA
    2. Veterinary Diagnostic Laboratory, Pharmacology Analytical Support Team (PhAST), Iowa State University, College of Veterinary Medicine, Ames, IA, USA
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  • L. W. Wulf,

    1. Veterinary Diagnostic Laboratory, Pharmacology Analytical Support Team (PhAST), Iowa State University, College of Veterinary Medicine, Ames, IA, USA
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  • S. Washburn

    1. Department of Veterinary Physiology and Pharmacology, Texas A&M University, College of Veterinary Medicine and Biomedical Sciences, College Station, TX, USA
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Abstract

The objectives of this study were to determine plasma concentrations and pharmacokinetic parameters of feed-grade chlortetracycline (CTC) in sheep after oral administration of 80 or 500 mg/head daily, divided into two equal doses given at 12-h intervals for 8 days. These are the approved, and commonly used but unapproved, feed additive doses, respectively, in the United States for the prevention of ovine infectious abortion.

Blood samples were collected just prior to dosing at 0, 12, 24, 72, 96, and 192 h, as well as 4, 8, 12, 24, and 36 h after the last dose, and noncompartmental pharmacokinetic analysis was performed to estimate elimination half-life and area under the plasma concentration–time curve (AUC).

Mean observed maximum CTC concentrations (Cmax) were 20.0 ng/mL (80 mg dose) and 101 ng/mL (500 mg dose). Mean apparent elimination half-life was 18 h (80 mg dose) and 20 h (500 mg dose).

Although published data do not exist to estimate plasma CTC concentrations necessary for the prevention of ovine infectious abortion, concentrations reached in our study suggest that either the FDA-approved and FDA-unapproved dosages are not high enough or that the pharmacodynamic parameter relating preventive dose to pathogen minimum inhibitory concentrations is yet to be determined.

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