Drug-induced diseases are commonly encountered and described as adverse drug reactions i.e. an undesirable effect of drug
treatment. There are two types of adverse drug reactions: Types A and B. A type A drug reaction is a predictable dose and/or
time dependent exaggerated response related to the primary (desired) or secondary (unwanted) pharmacological activity of the
drug administered. Lack of response caused by underdosing is also considered a type A drug reaction. A type B drug reaction
is an unpredictable dose and/or time-independent unrelated response referred to as a cytotoxic adverse reaction as it generally
causes damage to target cells. The parent drug and/or the production of potentially reactive metabolite(s) may be responsible
for the cytotoxicity. Contrarily to Type A drug reactions, Type B reactions are largely unavoidable and include some drug
allergies and all idiosyncrasies.
Organs most susceptible to Type A reactions are the highly perfused liver and kidneys as they are subjected to the highest
concentration of and exposure to systemic drugs. Organs most susceptible to Type B reactions causing drug-induced allergies
are organs that contain tissues acting as haptens such as skin and blood-forming units, and tissues that filter and trap immune
complexes such as the glomerulus and joints.
The clinical manifestation of an adverse drug reaction will depend on the type of drug reaction (A or B) and the organ(s)
involved. Allergic drug reactions, hepatotoxicity, nephrotoxicity, gastrointestinal irritation/toxicity, neurotoxicity, ototoxicity,
dermatological manifestations, endocrine system reactions, haematological dyscrasias and pulmonary toxicity have all been
identified for different drugs administered to companion animals. Fortunately, not all adverse drug reactions are clinically
relevant; however, reporting suspected reactions is important in assuring safe and efficacious drug use in animals.
1. Provide the practitioner with an overview of the different types of adverse drug reactions.
2. Provide the practitioner with a general understanding of the different organ-specific drug-induced diseases in the dog
and the cat.
3. Provide the practitioner with some specific examples of drug-induced diseases in the dog and cat.
4. Provide the practitioner with some insight as to how to avoid or handle the different drug-induced diseases.
5. Emphasize the importance of adverse drug reaction reporting to the pharmaceutical company and the Food and Drug Administration/Center
for Veterinary Medicine (FDA/CVM)