From the FDA Drug Label
The FDA drug label does not answer the question.
From the Research
Hydroxyzine should be used with extreme caution when combined with xylazine in horses due to the potential for severe sedation and respiratory depression, and its use should be carefully considered and monitored by a veterinarian. When administered with other sedatives or tranquilizers like acepromazine, xylazine, or detomidine, hydroxyzine can cause enhanced sedation and potentially dangerous cardiovascular depression 1. The typical dose of hydroxyzine in horses is 0.5-1.0 mg/kg given intramuscularly or intravenously, but this should be reduced when used in combination therapy. Particularly concerning is the combination with opioids, which can increase the risk of respiratory depression. Hydroxyzine should not be combined with epinephrine as it may reduce epinephrine's effectiveness. When used with NSAIDs, monitor for increased gastrointestinal irritation. The drug works primarily as an antihistamine with sedative properties by blocking H1 receptors in the central nervous system. Always observe horses for at least 30 minutes after administration of hydroxyzine combinations to ensure no adverse reactions occur, and have emergency drugs like epinephrine, atropine, and flumazenil available if needed.
Some key points to consider when using hydroxyzine in combination with other medications in horses include:
- The potential for enhanced sedation and cardiovascular depression when combined with sedatives or tranquilizers like xylazine or detomidine 1
- The increased risk of respiratory depression when combined with opioids
- The potential for reduced effectiveness of epinephrine when combined with hydroxyzine
- The need for careful monitoring and observation after administration of hydroxyzine combinations to ensure no adverse reactions occur
- The importance of having emergency drugs available if needed.
It's also important to note that current guidelines have limited applicability to patients with comorbid conditions, and the use of hydroxyzine in combination with other medications should be carefully evaluated on a case-by-case basis 2. Additionally, the use of rational and irrational fixed-drug combinations should be carefully considered, and the potential benefits and risks of combination therapy should be weighed carefully 3. However, the most recent and highest quality study on the topic of xylazine, which is a key component of the question, is from 2023 and highlights the urgent need for proactive strategies to combat the negative impacts of xylazine on population health 4.