My Dog Ate Doxycycline 100mg, What Do I Do?

Your dog ate 9? ...I would call the vet for advice. My dog is 32 to 34 lbs - about the size of a border collie (which we suspect her father was). She was prescribed 100 mg tablets of Doxycycline for a condition that she has and I was told to give her 1 & a half tablets twice per day- which brings us up to a whopping total of 3 tablets per day. And she's completely fine with 3. Three tablets would be safe, if taken with food. The instructions say TAKE WITH FOOD in all CAPS. Just call & ask the vet. Or Google ways to possibly have your dog throw up. He/she might just throw up anyway, I imagine that many pills would upset his/her stomach.

My dog is taking 100 mg doxycycline and he is going crazy with his ears. He is constantly itching and shaking his head. Is this from the medicine?

You should make it vomit somehow so that its internal system does not get affected by this heavy dose of Doxycycline. One way of making it vomit is to add healthy amount of petroleum jelly in its diet as a lubricant. Take it vet immediately if it is not eating anything.