Effect of changes in urine pH on plasma pharmacokinetic variables of ampicillin sodium in horses

Patxi Sarasola From the Department of Veterinary Pharmacology, University of Glasgow Veterinary School, Bearsden Road, Bearsden, Glasgow G61 1QH, Scotland, UK.

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Linda J. I. Horspool From the Department of Veterinary Pharmacology, University of Glasgow Veterinary School, Bearsden Road, Bearsden, Glasgow G61 1QH, Scotland, UK.

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Quintin A. McKellar From the Department of Veterinary Pharmacology, University of Glasgow Veterinary School, Bearsden Road, Bearsden, Glasgow G61 1QH, Scotland, UK.

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Summary

The effect of urine pH on plasma disposition of ampicillin sodium was evaluated. A single dose of 10 mg/kg of body weight was administered iv to Thoroughbreds with alkaline (pH > 8.0) or acidic (pH < 4.5) urine. Urine alkalinity was achieved and maintained by oral administration of up to 400 mg of sodium bicarbonate/kg/d, and acidity was achieved and maintained by oral administration of up to 400 mg of ammonium chloride/kg/d.

Ampicillin sodium was measured in the plasma of horses by use of an agar diffusion microbiological assay with Bacillus subtilis as the test organism. The plasma disposition kinetics of ampicillin sodium best fitted a 2-exponential decay pattern, and statistically significant differences were not evident in elimination half-life, area under the plasma concentration time curve, volume of distribution, or body clearance rate between horses with alkaline or acidic urine.

Results indicate that changes in urine pH over a range encountered in clinically normal horses are unlikely to affect plasma pharmacokinetic variables of ampicillin sodium after iv administration of the drug.

Summary

The effect of urine pH on plasma disposition of ampicillin sodium was evaluated. A single dose of 10 mg/kg of body weight was administered iv to Thoroughbreds with alkaline (pH > 8.0) or acidic (pH < 4.5) urine. Urine alkalinity was achieved and maintained by oral administration of up to 400 mg of sodium bicarbonate/kg/d, and acidity was achieved and maintained by oral administration of up to 400 mg of ammonium chloride/kg/d.

Ampicillin sodium was measured in the plasma of horses by use of an agar diffusion microbiological assay with Bacillus subtilis as the test organism. The plasma disposition kinetics of ampicillin sodium best fitted a 2-exponential decay pattern, and statistically significant differences were not evident in elimination half-life, area under the plasma concentration time curve, volume of distribution, or body clearance rate between horses with alkaline or acidic urine.

Results indicate that changes in urine pH over a range encountered in clinically normal horses are unlikely to affect plasma pharmacokinetic variables of ampicillin sodium after iv administration of the drug.

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