When two or more medicines are taken at the same time, they can work together in one of three ways: additive, synergistic, or antagonistic interaction.
What is synergistic interaction?

Two drugs can have a synergistic effect if they increase each other's effectiveness when taken together. There are two main types of synergistic drug interactions. Additive synergistic reactions are those in which the combined effects of two or more drugs are equal to the sum of those drugs' individual effects. Enhanced synergy occurs when the combined effect of the drugs is greater than the sum of those drugs' individual effects.

Explanation:

if you think your dog may have been exposed to a toxin, the best thing to do is to check the label of the item you think your pet ingested. read the information about toxicity. often, but not always, the information on packaging regarding children is relevant to dogs and some manufacturers even discuss dog toxicity. if there is an 800 number on the package – call them! it’s also recommended that you call your veterinarian to confirm the recommendations. if you go to your veterinarian, take all packaging and any information you have on the product.