Call the number on the container it came in. If they don't know, I would call an after hours practice and just ask them. I highly doubt they would not give you the truth. If they feel it's not good to wait, don't. If you choose not to call anyone, watch the dog very closely for symptoms that change quickly. They often eat awful things without much problem. Google your question too while you are waiting. If I knew more about this situation you have, I could give you more succinct answers.
Best of luck.