Pharmacokinetics of intravenous continuous rate infusions of sodium benzylpenicillin and ceftiofur sodium in adult horses.

The research article discusses an experiment to determine the concentrations of sodium benzylpenicillin and ceftiofur sodium in horse plasma when administered through continuous intravenous infusion (CRI). These drugs are maintained at high plasma concentrations for a specific period, which could be a more effective treatment method than intermittent bolus administration.

Research Process

• The study involved six adult Thoroughbred mares, with no recent history of taking antibiotics. Their average weight was 544 kilograms.
• The mares underwent two separate experiments, each spaced 14 days apart. For each experiment, the mares were confined to individual stables.
• Two catheters were placed in each mare: one in the left jugular vein for the drug administration via CRI and another one in the right jugular vein designed for intermittent blood sampling.
• The researchers also collected synovial fluid samples from the mares’ carpal joints after the administration of ceftiofur to study how the drug disseminates into joint spaces.

Results

• The results showed that plasma concentrations reached levels above the known minimum inhibitory concentrations (MIC) for common horse pathogens within a minute after a bolus injection. This high concentration was maintained for the duration of the CRI.
• The plasma concentrations remained above the MIC for 48 hours for ceftiofur and 12 hours for benzylpenicillin. This was the total duration of the CRI for each drug.
• Samples of synovial fluid revealed that by the end of the infusion, concentrations of ceftiofur were about 46% of those in the plasma.

Conclusions and Clinical Importance

• The loading dose and CRI method used in the study required less of the drug yet maintained high plasma concentrations for the entire infusion period. This implies that it could be more efficient than intermittent bolus administration.
• Basing on the pharmacological parameters obtained from the study, the recommended dosages are: a loading dose of 2.5 mg/kg and a CRI of 200 µg/kg/h to achieve plasma ceftiofur concentrations of 4 µg/mL, and a loading dose and CRI of 1.3 mg/kg and 2.5 µg/kg/h, respectively, to achieve plasma benzylpenicillin concentrations of 2 µg/mL.