The most effective medication that can be used to stop an immediate seizure is diazepam. The most common reason for diazepam failing to stop a seizure is that enough was not given. In general, use 1 ml IV for small dogs (5 - 10 kg), 2 ml IV for medium dogs (10 - 20 kg) and 3 ml or more IV for large dogs (greater than 20 kg). For cats use 0.25 - 1 ml IV. If you cannot get IV access give double the IV dose rectally. Use a red rubber feeding tube inserted about 4 - 6 inches in the rectum and given as a bolus. If after giving a dose of diazepam the seizure does not stop within 2 - 3 minutes (IV) or 5 min (rectal) then give another dose. It is not that uncommon to have to give 2 - 4 doses of valium before the seizure stops. It sounds like a lot but it is very safe. If an animal has compromised liver function or you are suspicious of liver disease (shunt or cirrhosis etc...) then give 1/4 of the estimated dose (diazepam or phenobarbital). Once the seizure is stopped you can give a loading dose of phenobarbital or potassium bromide. If you are going to refer the patient immediately, it might be better to wait on the loading dose so a more accurate exam can be performed. If the patient continues to have seizures after the initial doses of valium, they should be placed on a valium constant rate infusion. Use the amount of valium that it took to stop the seizure and give it over one hour as a CRI.
Question: My dog was just diagnosed with epilepsy
Several medications are now prescribed as secondary, add-on medication for dogs whose seizures are not controlled by either phenobarbital or potassium bromide. One of the most promising, according to Dr. Boothe, is zonisamide, which can be used as both a sole medication and an add-on with few side effects.
Seizures in Dogs - Causes, Diagnosis and Treatment - The Spruce
Piper has been taking Phenobarbital (160 mg) twice a day for his seizures. He takes Potassium Bromide as well. One of the typical side effects of Phenobarbital is that it can make dogs a bit clumsy (ataxia) and weak in the rear end. It also often increases the amount that dogs drink and thus pee out and can make them quite ravenous so you may also need to watch for unusual chewing activity as you see how Pb is going to affect your dog.
Sometimes, after a couple of weeks the dog's body adjusts and adapts to the medication and problem side effects my decrease a bit. I noticed that when we were still increasing Piper's meds, looking for the optimal dose for him, that he had an adjustment period of a couple of week or more with each dosage increase.
For Piper, I've found a bit of wobbliness is a price we have to pay for decent seizure control.
Since you are new to dealing with seizures, I'll post my favorite links to excellent seizure info and support:
This site also hosts a great email list for owners of epileptic dogs
Good luck in managing your hound's seizures.
Phenobarbita Is Used to Treat Seizures in Dogs and Cats - The Spruce