Guaifenesin: cardiopulmonary effects and plasma concentrations in horses.

The research analyzed the cardiorespiratory effects of guaifenesin administration in horses, as well as the impact of a preexisting xylazine dosage. Also, they studied guaifenesin plasma concentrations in horses and pregnant mares, revealing that this drug can cross the placental barrier.

Dosage and Administration

• The researchers administered two sets of drugs to the horses for this study – guaifenesin alone and xylazine followed by guaifenesin. Subsequently, they measured the effects these substances had on the horses’ cardiopulmonary functions.
• The dose of guaifenesin that was necessary to induce lateral recumbency or side-lying position in adult horses was found to be approximately 134 +/- 34 mg/kg. This dosage produced insignificant changes in several parameters like heart rate, respiratory rate, right atrial pressure, pulmonary arterial pressure, and cardiac output.
• However, pre-administration of xylazine to the horses significantly reduced the dose of guaifenesin required to bring about the same effect to 88 +/- 10 mg/kg. This combination also led to significant momentary decreases in heart rate, respiratory rate, cardiac output, and oxygen partial pressure, while significantly increasing the central venous pressure.

Plasma Concentrations and Cross-Placental Transfer

• Simultaneously, the researchers measured the plasma concentrations of guaifenesin at the time of lateral recumbency in both groups of horses.
• In horses given only guaifenesin, the concentrations of the drug were found to be 313 +/- 108 microgram/ml, and in those being administered xylazine followed by guaifenesin, the concentrations were measured to be 277 +/- 83 microgram/ml.
• The study also evaluated the transfer of guaifenesin across the placental barrier in pregnant mares. The results showed that around 30% of the mare’s guaifenesin concentration was found in the neonate immediately after birth, signaling that guaifenesin does cross the placental barrier in measurable amounts.