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Drug disposition and biotransformation in the developing beagle dog
D J Ecobichon1, A S D'Ver, W Ehrhart
1Department of Pharmacology and Therapeutics, McGill University Montréal, Quebec, Canada.
Summary
Drug metabolism and elimination in developing beagle pups show significant age-related changes. Acetaminophen and phenytoin clearance increased with age, indicating developing biotransformation capabilities in young dogs.
Area of Science:
- Pharmacokinetics and Drug Metabolism
- Developmental Biology
- Veterinary Pharmacology
Background:
- Understanding drug biotransformation and elimination in developing organisms is crucial for assessing potential toxicities.
- Age-related changes in metabolic pathways can significantly alter drug efficacy and safety profiles.
- Beagle pups serve as a relevant animal model for studying perinatal drug disposition.
Purpose of the Study:
- To investigate the developmental changes in drug metabolism and elimination in male and female beagle pups.
- To assess the biotransformation and clearance of acetaminophen, phenobarbital, and phenytoin across different postnatal ages.
- To evaluate the utility of this animal model for perinatal drug toxicity studies.
Main Methods:
- Single intravenous doses of acetaminophen, phenobarbital, or phenytoin were administered to beagle pups at 4, 10, 20, 40, and 60 days of age.
- Serial blood samples were collected to determine plasma drug concentrations and calculate pharmacokinetic parameters, including elimination half-life (beta t/2).
- Metabolite profiles, specifically sulfate and glucuronide conjugates of acetaminophen and para-hydroxylated phenytoin (pHPPH), were analyzed.
Main Results:
- Acetaminophen elimination half-life significantly decreased with age, with a 4.5-fold shorter half-life in 40- to 60-day-old pups compared to 4-day-old pups.
- Acetaminophen metabolism shifted from sulfate conjugation in younger pups to glucuronide conjugation in older pups, with increased glucuronide elimination.
- Phenytoin elimination half-life showed a dramatic 10-fold decrease between 4 and 60 days of age, with pHPPH detected only in younger pups.
Conclusions:
- Beagle pups exhibit significant age-dependent maturation of drug biotransformation and elimination pathways for acetaminophen and phenytoin.
- The observed changes suggest a developing capacity for drug metabolism, impacting clearance rates and metabolite profiles.
- This animal model, utilizing serial blood sampling, shows potential for perinatal drug toxicity research.