Placentitis, an inflammation of the placenta caused by bacteria such as Streptococcus equi subspecies zooepidemicus, is one of the leading causes of foal death. It’s challenging to treat, and researchers are still trying to identify effective therapies, particularly antibiotics. Currently, many practitioners administer the antibiotic ceftiofur crystalline free acid (CCFA, trade name Excede), but this drug does not penetrate the placenta well. Theorizing that its oil-based vehicle might be to blame, one group of researchers tested the efficacy of another form of ceftiofur—ceftiofur sodium (trade name Naxcel).

"We hypothesized that ceftiofur sodium would pass the fetal placental barrier," said Margo Macpherson, DVM, MS, Dipl. ACT, professor of large animal reproduction at the University of Florida College of Veterinary Medicine, in Gainesville. She presented the study’s results at the 2014 American Association of Equine Practitioners Convention, held Dec. 6-10 in Salt Lake City, Utah.

In the study, Macpherson and colleagues administered intramuscular ceftiofur sodium at commonly used low (2.2 mg/kg) or high (4.4 mg/kg) doses to six and five healthy pregnant pony mares, respectively. The mares ranged from Day 270 to Day 326 of gestation. The researchers took eight plasma samples at varying time points up to 24 hours after ceftiofur administration to determine its pharmacokinetics (how the drug levels are processed and maintained in the body).

The researchers then used eight of the mares in the second part of the study. Each mare received 4.4 mg/kg ceftiofur sodium daily for three days, at which time the researchers induced foaling. They collected allantoic and amniotic fluid, plasma (from mare and foal), colostrum, and placental samples at foaling and again 24 hours later