Age-dependent pharmacokinetics of phenylbutazone in calves

Area of Science:

• Veterinary Pharmacology
• Animal Science
• Drug Metabolism

Background:

• Phenylbutazone (PBZ) is a non-steroidal anti-inflammatory drug used in veterinary medicine.
• Understanding drug pharmacokinetics in different age groups is crucial for safe and effective treatment.
• Age-related differences in drug metabolism and elimination can significantly impact efficacy and toxicity.

Purpose of the Study:

• To investigate the pharmacokinetics of phenylbutazone (PBZ) in calves of different ages.
• To determine how age influences the elimination half-life and body clearance of PBZ.
• To assess the potential for drug accumulation with repeated dosing in young calves.

Main Methods:

• Intravenous administration of PBZ (22 mg/kg) to three age groups of calves (1-month-old vs. 3-6 months old).
• Collection of heparinized blood samples at defined intervals post-administration.
• Quantification of PBZ and its metabolites in plasma using high-performance liquid chromatography (HPLC).

Main Results:

• One-month-old calves exhibited significantly longer PBZ elimination half-lives (twice as long) compared to older calves.
• Total body clearance of PBZ was 40-50% lower in the youngest group.
• Mean elimination half-lives ranged from 39 to 94 hours, indicating prolonged drug presence.

Conclusions:

• Younger calves (1-month-old) demonstrate reduced PBZ clearance and prolonged elimination, suggesting immature metabolic pathways.
• The extended half-lives highlight a risk of phenylbutazone accumulation with repeated dosing in very young animals.
• Clinical use of PBZ in calves necessitates age-specific dosage adjustments and careful monitoring to prevent adverse effects.