Plasma histamine concentrations in horses administered sodium penicillin, guaifenesin-xylazine-ketamine and isoflurane with morphine or butorphanol.

The study investigates how certain drugs administered to horses during surgery, specifically sodium penicillin, guaifenesin-xylazine-ketamine (GXK), isoflurane, morphine and butorphanol, influence histamine levels. The research indicates an increase in histamine concentrations due to GXK, whilst showing similar levels for morphine and butorphanol.

Research Design and Methodology

• The study is prospective in nature with a randomized method. It involves 44 client-owned horses, confirming the real-world significance of the findings.
• Anesthesia for the horses was induced with xylazine followed by ketamine-diazepam, while GXK was used to maintain it during surgical preparation.
• The horses were divided into two groups. The morphine group (M) consisted of 15 horses given isoflurane along with intravenous morphine at 0.15 mg/kg and 0.1 mg/kg/hour. The butorphanol group (B) also had 15 horses, also administered isoflurane, this time with butorphanol at 0.05 mg/kg and 0.01 mg/kg/hour.
• The researchers measured histamine and morphine concentrations before the injection of the opioid (at time 0), and after intervals of 1, 2, 5, 30, 60, and 90 minutes.

Second Study

• In a following study, the research team then measured the plasma histamine levels in 14 different horses before drug administration. This served as the baseline measurement.
• These measurements were taken again a quarter of an hour after intravenous sodium penicillin was administered, and another 15 minutes after beginning GXK infusion.

Data Analysis

• For the analysis, the researchers employed anova for repeated measures, while the Pearson correlation was used to compare morphine and histamine concentrations.

Significant Findings

• Results indicated a difference in histamine levels between the baseline (3.2 ± 2.4 ng/mL) and GXK (5.2 ± 7.1 ng/mL). A similar difference was seen between the baseline and time 0 in both Group B (11.9 ± 13.4 ng/mL) and Group M (11.1 ± 12.4 ng/mL).
• However, there was no significant difference between baseline histamine levels and post-penicillin administration or between Group M and Group B.
• Morphine concentrations were observed to be higher at 1 minute after injection (8.1 ± 5.1 ng/mL) than at 30 minutes (4.9 ± 3.1 ng/mL) and 60 minutes (4.0 ± 2.5 ng/mL).

Conclusions

• It was concluded that while GXK significantly increased histamine concentrations, morphine and butorphanol were associated with similar levels throughout their use.