Osteoarthrosis in dogs and cats: medical treatment
Osteoarthrosis is usually approached with a conservative, multimodal treatment that combines the use of nonsteroidal anti-inflammatory drugs with nutritional management, weight control and limited exercise.
Introduction
The management of overweight, controlling exercise and the right nutritional supplements are key to the treatment of this long-term degenerative process.
The most widely used drugs, which have also proven the most effective, are classed as either clinical sign modifiers or structural modifiers. The former are primarily used to treat pain. Structural modifiers, on the other hand, seek to delay, halt or reverse pathological changes in the joint tissue.
Nonsteroidal anti-inflammatory drugs
This group of medicines corresponds to drugs that address the clinical signs, and it is the most widely used class of drugs in dogs. The range of nonsteroidal anti-inflammatory drugs (NSAIDs) marketed for use in cats is far more limited than for dogs, and they must be used with greater caution. [1]
Most NSAIDs work by inhibiting the cyclooxygenase (COX) enzyme, which is known to play a key role in the inflammatory process and onset of pain in patients with osteoarthritis. [1] There are two COX isoenzymes: COX-1 and COX-2. COX-1 produces prostaglandins that are essential for basic physiological functions, and it is expressed in several tissues, including gastrointestinal cells, platelets, endothelial cells and renal cells. Therefore, COX-1 inhibition can cause alterations in any of the contingent systems. COX-2, however, is considered an inducible enzyme that is overexpressed in the presence of inflammation. COX-2 expression in synovial fluid and subchondral bone was found to be higher in dogs with osteoarthritis compared to healthy dogs. [2] However, it also has a cytoprotective effect on the gastrointestinal mucosa and is found in the kidneys and brain. Therefore, research to manage pain in osteoarthritic dogs has focused on discovering drugs that induce maximum inhibition of COX-2 with minimal impact on COX-1. This ensures an analgesic effect without the well-known gastrointestinal and renal consequences of COX-1 inhibition. [1]
The side effects of NSAIDs are not fully understood. Nonetheless, some studies report that the most common side effects associated with the use of these drugs are loss of appetite, vomiting and diarrhoea. Unfortunately, the actual incidence in dogs treated with NSAIDs is unknown. [1] Some COX-1-selective NSAIDs can alter thromboxane synthesis and consequently platelet activity.COX-2 mediates prostacyclin, a prostaglandin that inhibits the formation of vascular thrombosis in a process that can be affected by the administration of COX-2-selective NSAIDs. Lastly, COX-1 and COX-2 both play a key role in blood flow and ion transport in nephrons. This impact on renal function is very important in patients with predisposing factors, such as heart disease, pre-existing kidney or liver diseases, old age or a hypovolaemic state. [1] The administration of NSAIDs in any of these cases must be fully justified and with particular care.
Common NSAIDs and their recommended doses [3]:
- Carprofen:
- In dogs: 4 mg/kg/day intravenously (IV), subcutaneously (SC) or orally (PO) for up to 7 days, this can then be reduced to 2 mg/kg/day based on clinical response.
- In cats: 4 mg/kg as a single dose peri-operatively (IV or SC).
- Meloxicam:
- In dogs: 0.2 mg/kg SC or PO as a single or initial dose. It can be administered long-term at a dose of 0.1 mg/kg/day PO.
- An initial dose of 0.1 mg/kg PO is recommended for the treatment of chronic pain in cats, reducing to 0.05 mg/kg/day PO as a maintenance dose.
- Firocoxib:
- In dogs: 5 mg/kg/day PO.
- In cats: do not use.
- Robenacoxib:
- In cats and dogs: 2 mg/kg/day SC with a maximum of two doses. Administration should then be switched to PO at a dose of 1–2 mg/kg, based on response.
Other analgesics
- Amantadine: is an N-methyl-D-aspartate (NMDA) receptor antagonist. NMDA receptors have been linked to the sensation of prolonged pain caused by inflammation, known as neuropathic pain. [1] When used in combination with meloxicam to treat osteoarthritis in dogs, it was shown to produce better results than meloxicam alone. [4] Recommended dose [3]:
- In dogs: 3–5 mg/kg/day PO.
- In cats: 1–4 mg/kg/day PO (there is no literature evidence to support doses).
- Gabapentin: is a gamma-aminobutyric acid (GABA) analogue, which has obtained good results in human medicine for the treatment of neuropathic pain. [1] Its exact mechanism of action remains unknown, but it seems to be related to N-type calcium channels. Since Gabapentin is excreted by the kidneys, the dose or the dosing frequency should be reduced in patients with renal impairment. Recommended dose [3]:
- In dogs: 10–20 mg/kg every 6–8 hours PO (a gradual increase is recommended based on the dose–response relationship).
- In cats: 5–10 mg/kg every 8–12 hours PO (a gradual increase is recommended based on the dose–response relationship).
- Acetaminophen: paracetamol, also known as acetaminophen, is a centrally acting analgesic. Its mechanism of action is not fully understood. It is considered a very safe drug; one study reported administering doses of up to 100 mg/kg without observing any adverse side effects. [5] Recommended dose [3]:
- In dogs: 10–20 mg/kg every 8–12 hours IV or PO.
- In cats: it must not be used under any circumstances. It is highly toxic.
- Codeine: also known as methylmorphine, is a natural alkaloid obtained from the opium plant and is considered a prodrug. Its in vivo metabolism produces morphine at a rate of 5–10%. The effect of codeine alone has not been studied in cats and dogs, but promising results have been obtained in combination with paracetamol. Recommended dose [3]:
- In dogs: 1–2 mg/kg every 6–12 hours PO.
- In cats: 0.5–2 mg/kg every 6–8 hours PO.
- Corticosteroids: are somewhat controversial. They evidently have an anti-inflammatory effect, but it is transient and they are not recommended for long-term use. Intra-articular injections can be employed as a rescue therapy when justified by the side effects and complications.
Conclusions
There are many pharmacological options available, and vets must assess patients on a case-by-case basis to determine the ideal treatment. Remember that the treatment of osteoarthritis in cats and dogs should be multimodal as the pharmacological therapy should always be supported by a balanced diet, nutritional supplementation and controlled exercise.
Osteoarthritis is a degenerative process rather than just a disease, so each patient’s medication should be reviewed periodically. This particularly applies to long-term treatment regimens, elderly patients and those with concomitant diseases. Communication with the owner is essential to ensure the highest quality of life for as long as possible.
