Narcotics and local anesthetics.

The research discusses the use of narcotics and local anesthetics for pain relief in horses, highlighting the benefits and potential risks of each type of medication, the mechanisms through which they operate, and the potential for their optimization and safe use.

Opioids and Pain in Horses

• The study emphasizes the importance of acknowledging and addressing animal pain, noting that it can trigger changes in the central and autonomic nervous systems and the endocrine system.
• According to the research, horses have an inherent system designed to manage pain—this system is centered in the brainstem and spinal cord and can adjust the perception of pain and the responses to it.
• Endorphins and enkephalins, endogenous opioid peptides discovered recently, seem to contribute to this system and are triggered by stress.

Mechanism of Opioids In Pain Management

• Opioids like narcotic analgesics function by selectively inhibiting pain-sensitive cells.
• These analgesics may operate through multiple opioid receptors. Each subclass of receptor has distinct pharmacological characteristics.
• Traditional opioids that act on mu (morphine) receptors usually result in pain relief, increased movement, cardiorespiratory stimulation, and a decline in intestinal peristalsis in horses.
• Opioids that act on kappa receptors result in pain relief, drowsiness, unsteadiness, and minor autonomic effects in horses. The kappa opioids are potentially useful as analgesics in equine species due to their lack of exciting effects.

Using Local Anesthetics

• Local anesthetics suppress all excitable cells and can reduce sensory, motor, and muscle function.
• These anesthetics don’t selectively act on pain fibers, although pain is one of the first sensations lost after a nerve block.
• The effectiveness of local anesthetics can be improved by increasing the pH outside the neuron, cooling the nerve, increasing neural activity, using vasoconstrictor or hyaluronidase coadministration, slowing systemic absorption, extending drug metabolism duration, and using agents with high lipid solubility.

Commonly Used Local Anesthetics and Detection

• Procaine, lidocaine, and mepivacaine are among the most widely used and researched agents related to horses. These agents, and/or their metabolites, can be easily detected in urine—in some cases, for extended periods.