sulfadiazine and trimethoprim suspension in neonatal foals

These researchers found that 11 mg/lb (24 mg/kg) for 10 days safe in newborn foals and reached therapeutic levels for sensitive bacteria. I would expect similar results with sulfamethoxazole preparations. These are higher doses than have been previously recommended and good to know.
DrO

Pharmacokinetics of a sulfadiazine and trimethoprim suspension in neonatal foals
J Vet Pharmacol Ther. 2020 Dec 1.
Authors
Elsbeth Swain O’Fallon 1 , Patrick McCue 1 , Sangeeta Rao 1 , Daniel L Gustafson 1
Affiliation

1 Department of Clinical Sciences, James L. Voss Veterinary Teaching Hospital, Colorado State University, Fort Collins, CO, USA.

Abstract

There is limited investigation of neonatal foal pharmacokinetic parameters for the antimicrobial combination of sulfadiazine (SDZ) and trimethoprim (TMP). Neonatal pharmacokinetic investigation of the sulfadiazine-trimethoprim combination is required to ensure safe and effective utilization in this population. The purpose of this study was to determine the pharmacokinetics of sulfadiazine-trimethoprim in five healthy neonatal foals with oral administration at 24 mg/kg every 12 hr (hrs) for 10 days. Blood samples were collected at serial time points at approximately 72 hr of age (steady-state) and at days 5 and 10 to monitor the influence of age within the neonatal period. Pharmacokinetic parameters were determined using a one-compartment model analysis, and mean ± SD was calculated. Cmax was 37.8 ± 13.4 μg/ml (SDZ) and 1.92 ± 0.25 μg/ml (TMP). Tmax was 1.4 ± 0.6 hr (SDZ) and 1.4 ± 0.4 hr (TMP). Cmin for SDZ and TMP was 16.84 ± 8.46 μg/ml and 0.46 ± 0.24 μg/ml, respectively. Elimination half-life was 10.8 ± 6.1 hr (SDZ) and 6.5 ± 2 hr (TMP). AUC0 → ∞ was 667 ± 424 μg × hr/ml (SDZ) and 21.1 ± 5.3 μg × hr/ml (TMP). Foals remained healthy, and the plasma concentration of sulfadiazine-trimethoprim reached levels above MIC(90) for Streptococcus equi ssp. (SDZ/TMP): 9.5/0.5 μg/ml).