Principles of analgesic drug therapy.

The drugs most often used for pain relief in animals are the nonsteroidal antiinflammatory drugs (NSAIDS) and the opioid analgesics. The NSAIDS are effective, inexpensive, and long-acting drugs, but their degree of analgesia is limited by the adverse effects at high doses. The most common adverse effect from NSAIDS is gastritis and gastrointestinal hemorrhage and ulceration. This is most common from high doses, or from using NSAIDS not appropriate for dogs such as ibuprofen or indomethacin. The NSAIDS used in dogs include aspirin, phenylbutazone, naproxen, piroxicam, ketoprofen, and carprofen. Carprofen is a new drug with a low incidence of side effects and its popularity is increasing at a fast rate. For more acute pain, especially acute pain from surgery or trauma, opioids are frequently administered. Opioids have the advantage of higher efficacy when the dose is increased. The incidence of adverse effects is low, but side effects of sedation are common. An important disadvantage of opioids is their short duration and low oral absorption, which necessitates a frequent injection or i.v. infusion for most patients. Recent studies have established other applications for administration of opioids such as a transdermal fentanyl patch. These applications offer new possibilities for convenient administration.