Pain relief for dogs. Does the administration route modify the effect?
Acute pain occurs suddenly after a specific trauma or injury anddisappears as the damage heals. Chronic pain, by contrast, persists once the injury has healed or because the injury becomes chronic over time.
There are several families of analgesic drugs available to treat the two classes of pain, each with different mechanisms of action and administration routes.
Types of pain relief for dogs
1- NONSTEROIDAL ANTI-INFLAMMATORY DRUGS
These medicinal products form a very large group known as NSAIDs and are primarily used to treat acute pain. Examples from this family include aspirin, ibuprofen, ketoprofen, naproxen, etodolac, piroxicam and meloxicam.
These are the most commonly used drugs because they have very few side effects, are effective in the treatment of acute pain and offer multiple administration routes.
However, the side effects they do produce (gastric ulcers, gastrointestinal bleeding) mean they cannot be used for extended periods.
2- NARCOTIC ANALGESICS – OPIOIDS
Narcotics are opium derivatives and have been used to provide pain relief for dogs for many years. It could be said that they produce the most potent effect. This group of analgesics provides much better pain relief when administered in combination with a nonsteroidal anti-inflammatory drug (NSAID) rather than alone.
However, they have the disadvantage of being highly addictive, creating dependency and tolerance, so veterinary professionals should only prescribe them when other analgesics fail to produce results.
3- NON-NSAID, NON-OPIOID ANALGESICS
This group includes various drugs from different families which also have an analgesic effect and are often used to treat chronic pain in particular.
This group includes antidepressants, gabapentin and imipramine. They are not very effective for acute pain, in fact their main indication is the long-term treatment of pain.
After deciding which analgesic to use, we must select the most appropriate route of administration, which will modify the drug’s effect and in some cases, depending on the availability of the different routes, will also influence the initial choice of drug.
Analgesic drugs can be administered using the following routes:
1- Enteral: oral, sublingual, gastroenteral or rectal
2- Parenteral: intramuscular, subcutaneous and intravenous
3- Respiratory: primarily intranasal in analgesia
4- Topical: ophthalmic, auricular and transdermal
The intravenous parenteral route has the fastest mechanism of action and ensures complete bioavailability of the drug. Other routes, such as oral, may have a slower effect and lower bioavailability due to their first-pass hepatic metabolism. There are also rectal, nasal or sublingual alternatives to the oral route that allow for quick administration without requiring a needle, but while also ensuring rapid absorption through the mucosa. Finally, although absorption is slow via the transdermal route, it can be used for prolonged release of drugs without the need for a frequent intake.
So, the patient’s clinical status (vomiting) and the desired speed and duration of the analgesic effect, together with the potential side effects (e.g., infection in the case of parenteral use), will determine our choice of route.
