Welcome! I am Dr. Altman, a licensed veterinarian and happy to answer your questions today.
Unfortunately you cannot use this product intended for cats on dogs.
Directly from their website (http://www.frontlineplus.co.nz/products/frontline-plus/pages/frontline-plus-faqs.aspx):
Can I use the FRONTLINE Plus for Cats on my dogs and the FRONTLINE Plus for Dogs on my cats?
FRONTLINE Plus for Cats and FRONTLINE Plus for Dogs are not exactly the same. Only use the appropriate product for your dog or cat. However, FRONTLINE SPRAY can be used on both dogs and cats.
Especially with a Shih Tzu
which is a hypersensitive dog in my experience to topical products you want to use the correct product on Dexter. If you recently purchased the product you should be able to return it for the correct species.
I hope this information makes sense but please let me know how else I an assist you both today. I am on-line another 20 minutes this evening.
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