Systemic Analgesia
Introduction
Analgesia is a very important consideration in patient management, especially those that have undergone surgery. Many drugs can work synergistically to maximise their analgesic properties. This is termed multimodal analgesia. In some cases possible to use both systemic analgesia and local analgesic techniques in combination.
Systemic analgesia refers to the use of certain analgesic drugs that act at the appropriate receptor that can be found across the body. Classes of drugs includes opioids, non-steroidal anti-inflammatories (NSAIDS), as well as ketamine and gabapentin.
Opioids
Opioids are considered the most potent and efficious analgesic drugs available in veterinary medicine. They are used more commonly for acute pain. Opioids are both natural and synthetic and includes morphine, methadone, buprenorphine, pethidine and fentanyl among others. They act upon opioid repectors as full agonists, partial agonists, agonist-antagonists or full anatagonists.
Non-Steroidal Anti-Inflammatories
NSAIDS are used more commonly in the management of chronic pain and often used post operatively for longer term analgesia. They have other benefits over other drugs, such as opioids, as they lack certain side effects, do no alter behaviour and have anti-inflammatory properties. They produce analgesia by acting upon the COX enzyme preventing the production of prostaglandins, prostacyclin and thromboxanes.
Ketamine
Ketamine is a NMDA receptor antagonist. It is non competitive and is used commonly as an anaethetic. By inhibiting NMDA receptors, ketamine reduces the neuronal activity in the spinal cord. It may also have some effect at opioid receptors and/or noradrenergiv and serotonergic neurons.
Gabapentin
Used as an anticonvulsant in human medicine, Gabapentin has also been shown to have some analgesic properties also. It is thought to produce its effects via a secondary increase in gamma-aminobutyric acid (GABA) production which is an inhibitory neurotransmitter and may possible also act to block calcium channels within the membrane. ITs current use in veterinary patients is for neuropathic pain in dogs and cats. However, it does have some sedative properties.