To safely use a flea collar with Frontline, you should first check the active ingredients in the flea collar. If the flea collar contains the same active ingredients as Frontline, it is not recommended to use them together unless directed by a veterinarian. If the flea collar contains different active ingredients, it may be safe to use both products, but it is always best to consult with a veterinarian before using multiple flea and tick prevention treatments on your pet.
Additionally, some pets may have negative reactions to certain flea collars, including skin irritation or respiratory problems. If you notice any unusual symptoms in your pet after using a flea collar, it is important to remove the collar and contact your veterinarian.