Influence of Age on Half‐life of Trimethoprim and Sulphadoxine in Goats

The half‐life of trimethoprim is about 40 min. in adult goats and 4–5 times longer in newborn kids. During the neonatal period the half‐life decreases to the level found in adult goats when the body weight is about 10 kg corresponding to an age of 40–50 days. The half‐life of sulphadoxine is about 12 hours in adult goats and there is a tendency towards a longer half‐life in newborn and young kids, but the difference is not significant. The apparent volume of distribution for both trimethoprim and sulphadoxine is higher in newborn kids than in adult animals. The apparent volume of distribution for trimethoprim decreases during the neonatal period while that of sulphadoxine is nearly constant until an age of 16 weeks.