Opioids, synthetic drugs
The opioids are a diverse group of naturally occurring and synthetic drugs used primarily for their analgesic activity.
Opioids combine reversibly with specific receptors in the central nervous system, altering the transmission and perception of pain. The clinical effects of opioids depend on the amount and type of activity that the agent has at mu, kappa and delta receptors. The analgesic activity is associated with mu receptor action. Opioids can be mu opioid receptor agonists (e.g. morphine), partial mu agonists (e.g. buprenorphine), or agonist-antagonists (e.g. butorphanol). In addition, other factors, such as the presence or absence of pain, physical condition and drugs administered concurrently play a role.
Opioids should in general be used with caution in animals with respiratory disease or chest injuries, head trauma and/or increased cerebrospinal fluid (CSF) pressure or other central nervous system (CNS) dysfunction, and in geriatric or debilitated patients.
There are many other opioids that are approved only for use in humans are also used in small animal practice (e.g. morphine).