Like their human counterparts, it's not uncommon for some pets with complicated medical issues to require several medications as part of their treatment plan. Drug-drug interactions are well documented in human medicine, and many of the recommendations made for our companion animals are based on what's known regarding drug interactions in humans.


One prime example of this relates to the effect that one drug may have on another drug if they are taken in combination at the same time. In people, for example, it is known that patients who take the antibiotic ciprofloxacin along with a gastroprotectant (for gastric or duodenal ulcers) in combination, do experience a drug interaction. Specifically, when taken in combination, the gastroprotectant can significantly impair the absorption of the antibiotic. It's been shown that only 4% of the antibiotic actually winds up "bioavailable" or active to combat infection. Essentially, 96% winds up down the toilet. This phenomenon can result in therapeutic failure (an infection that does not clear), and can pave the way for resistant infections in the future. However, when there was a 2-hour delay and a 6-hour delay between the 2 drugs, the bioavailability increased to 83% and 96%, respectively.

Other types of drug interactions can occur and adversely affect the pet:

  • Some drug interactions are synergistic, meaning that one drug enhances the activity of the other. This can be beneficial in some instances, but an overly additive effect of one drug on another could also prove harmful or toxic.

  • One drug may also impair the metabolism or elimination of another drug from the body. This could result in an unintended prolonged effect of the drug, overdosage or toxicity.

What can you do to avoid these preventable scenarios? Pet owners should inform their veterinarian of all medications and supplements they administer to their pet. Being proactive and asking questions including: 1) whether multiple drugs can be given together / at the same time, 2) whether medications should be given with or without food, and 3) what to do if you accidentally miss a dose, will go a long way in ensuring your pet's well-being.

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