Pharmacokinetics of gentamicin in newborn to 30-day-old foals.

The study investigates the pharmacokinetics (how the body affects a drug) of gentamicin, a common antibiotic, in newborn to 30-day-old foals and their mothers. It reveals that the speed of gentamicin elimination increases in foals as they age and they eliminate the drug similarly to adult horses by day 30. The drug’s distribution and clearance also varies in relation to a foal’s age and individual factors.

Research Method

• Gentamicin was administered intravenously to six newborn Thoroughbred foals at various points during their first 30 days of life, as well as to their mothers at 40 days postpartum.
• The decay of serum gentamicin concentrations was analyzed using a two-compartment model, which separates the body into a central and a peripheral (’tissue’) compartment to better predict the drug’s movement within the body.

Findings

• The researchers found that the overall rate of gentamicin elimination in foals increased with age, showing significant increases from days 1, 10, and 15 to day 30.
• There was no difference in this rate between the day-30 foals and their mothers, implying that by their 30th day, the foals were metabolizing the drug similarly to mature horses.
• Significant interindividual differences were noted among the foals, suggesting individual characteristics can impact how the drug is metabolized.

Volume of Distribution (Vd)

• The Vd is a concept used to describe how a drug is dispersed throughout the body. This study found no changes in the drug’s Vd from days 1 to 30 in the foals.
• However, the Vd was consistently higher in the foals compared to their mothers – sometimes significantly so – indicating the drug spread more extensively within the foals’ bodies.

Total Body Clearance (ClB)

• ClB reflects how efficiently a drug is cleared from the body. The study found age-related differences, with the foals’ gentamicin clearance rates increasing as they grew older.
• By day 30, the foals’ ClB was similar to that of their mothers, except that the day-30 foals had a higher clearance rate.

Protein Binding

• In all tested groups, less than 30% of the gentamicin was protein-bound, a factor that affects a drug’s distribution and elimination. There were no age-related differences in this area.

This study advances understanding of how gentamicin works in young horses, important knowledge since the drug is often used to treat bacterial infections in this demographic. It underscores that foals’ age and individual factors should be considered when prescribing gentamicin to ensure effective and safe treatment.