Corticosteroids for dogs: side effects of prolonged use
Corticosteroids for dogs are lipophilic drugs that penetrate cells bypassive diffusion. When they bind to their cytoplasmic receptor, they dimerise and pass into the nucleus, where they bind to specific base sequences, thereby acting on DNA and enabling the synthesis of messenger RNA. This leads to an increase or decrease in the production of the corresponding proteins.
These changes are responsible for the main pharmacological action of corticosteroids, from their anti-inflammatory effects to their immunosuppressive and anti-allergic actions, as detailed in an article published in the journal IM Veterinaria1. However, some of these changes also produce unwanted side effects, especially when treatment continues over long periods.
Main side effects of prolonged use of corticosteroids in dogs
Immunosuppression. Corticosteroids inhibit antigen processing by macrophages, decrease the synthesis of certain proteins that may act as antibodies, and reduce the number of T-cells by depressing the lymphatic system. This means they have a significant immunosuppressive effect which, although it may be beneficial in the treatment of immune-mediated diseases, can also be harmful, as it predisposes the animal to different types of infections. Therefore, in some cases corticosteroids are coadministered with antibiotics to prevent the appearance of opportunistic infections.
Gastrointestinal problems. Two of the most common side effects of corticosteroids for dogs, especially when used at very high doses or for extended periods, are vomiting and diarrhoea. These drugs also cause an increase in the production of pepsin and hydrochloric acid, which, besides their inhibitory action on prostaglandin synthesis, can cause gastrointestinal ulcerations or even perforations, as revealed by a study conducted at the University of Bern2. This is one of the main reasons why they are used in conjunction with gastric protectors.
Delayed wound healing and growth of puppies. Corticosteroids block protein anabolism, that is, protein synthesis from precursors, which can cause muscle atrophy, decreased bone matrix and inhibited longitudinal bone growth. These mechanisms explain both the delayed growth of young animals and difficulties in wound healing. Consequently, they should not be used following surgery or in patients with an open wound.
Diabetes. Corticosteroids have an antagonistic effect on insulin, accelerate gluconeogenesis and inhibit the peripheral use of glucose, all of which increases glycogen deposition in the liver. This mechanism can induce hyperglycaemia or glycosuria, which can cause some animals to develop diabetes mellitus, especially those already in a prediabetic state.
Cardiovascular problems. Corticosteroid use has been associated with the development of some serious heart problems. A study conducted at the University of Arizona3 in human beings revealed that high doses of intravenous corticosteroids were associated with bronchospasm, arrhythmia and heart attacks. In dogs, a study at the University of Zurich4 revealed that the continued use of hydrocortisone increases blood pressure, which, according to the authors, “could be the result of irreversible peripheral vascular remodelling followed by increased wall stiffness and greater vascular resistance”.
Behavioural changes. In human medicine, the behavioural side effects in patients treated with corticosteroids have been widely documented. A study carried out at the University of Lincoln5 revealed similar results in dogs. Animals treated with corticosteroids were significantly less playful, more nervous, more restless, more fearful, less confident and tended to avoid strangers or unfamiliar situations. They were also more prone to barking and behaved more aggressively in the presence of food or when they were disturbed.
Other side effects related to corticosteroids include an increase in liver enzymes such as albumin. They can also provoke erythrocytosis and anaemia in dogs with adrenal insufficiency. Prolonged treatment may also induce Cushing’s syndrome due to increased cortisol.
Finally, another problem to bear in mind is that corticosteroids can interfere with the diagnosis of certain diseases, especially those of a neurological nature, as they affect the results of cerebrospinal fluid tests and magnetic resonance imaging tests.