Whenever we think about pain management we consider analgesics, i.e. drugs that eliminate pain. The word Analgesia, however, means absence of pain. In veterinary medicine, what we actually try to do is to alleviate pain, to provide comfort so that the patient may achieve a more speedy recovery.
Let´s revise some concepts:
Pain may be basically classified into two types: acute and chronic.
On the one hand, acute pain arises suddenly after a traumatic event, lesion or specific pathology and it disappears after a short period of time when healing is complete.
Chronic pain persists over time, its intensity varies, and sometimes becomes intermittent when its origin has not been completely removed or because the lesion becomes chronic.
Nowadays, there are many analgesic drugs to treat acute and chronic pain, with different mechanisms and routes of administration. They belong to different chemical families.
1- Non-steroidal anti-inflammatory drugs
These drugs are commonly known as NSAIDs and they are a large group of active ingredients, which are not always chemically related, and which are principally used to treat acute pain. For example: ketoprofen, piroxicam, meloxicam, coxibs, tolfenamic acid, etc.
They are the most used drugs because they have few adverse reactions, they are effective for the treatment of acute pain and they can be found in many different dosage forms. Their main disadvantage is that patients can have adverse reactions at the gastrointestinal level. Due to that, it is important to respect the dose and the length of treatment suggested for each species.
2- Narcotic analgesics – opiates
They are compounds that belong to the same family, and they are opium derived. They have been used to alleviate pain in dogs for many years. They have a potent analgesic action, they may even be the most potent analgesic drugs, because of this, they are the drugs of choice when pain is severe.
Tramadol, buprenorphine, morphine and fentanyl belong to this group.
Analgesics belonging to this group can be administered in concomitance with Non-steroidal anti-inflammatory drugs (NSAIDs) thereby obtaining analgesic synergy.
3- Non-opiate, non-nsaid analgesics
Within this group we may find several drugs belonging to different families, which are useful in other pathologies but which also have an analgesic effect and may be specifically used to treat chronic pain.
We can find antidepressants: gabapentin, pregabalin and imipramine. They are not very effective to treat acute pain, they are mainly used in the treatment of long-term pain.
Which are the most commonly used routes of administration?
1- Oral
2- Parenteral (intramuscular, subcutaneous or intravenous)
3- Topical: Ocular, otic and transdermal-
The intravenous parenteral route is the one that gives the fastest and total bioavailability.
Other routes, such as the oral, may have a slower effect and lower bioavailability due to hepatic first-pass metabolism.
There are also other less common alternative administration routes, such as rectal, nasal or sublingual, which allow for rapid absorption of the drug through the mucous membrane.
Finally, absorption via transdermal route is slow but it allows for prolonged release.
Drugs called disease modifiers (in general chondroprotective and osteoarticular drugs) deserve a whole new chapter as regards the treatment of chronic pain, they reduce pain by means of the recovery of the normal physiology, anatomy and mobility of the joint. These drugs can be administered by injection first, and administration can later continue through the oral route. All this can improve pain management.
Bibliography:
Anderson M.A.: Oral chondroprotective agents .Part II. Comp.Cont. Ed. 1999;21:9. 861-864.
Clark D.M.: Current concepts in the treatment of degenerative joint disease. Comp. Cont Ed.1991;13:9. 1439-1447.
Clark D.M.: The biochemistry of degenerative joint disease. Comp.Cont. Ed.1991;13:2. 275-284.
Nelson R.W.,Couto G.C.: Small Animal Internal Medicine. Mosby , 2nd Ed.1988.345-666
Kirk.R.: Current Veterinary Therapy XI,.McGraw Hill-Interamericana.pp.212-214
Lippiello.L.: Sinergia Metabólica de la Glucosamina HCl y el Condroitín Sulfato. Condroprotección in vivo.España.2000. (In vivo chondroprotection and metabolic synergy of glucosamine and chondroitin sulfate. Spain 2000)
