Hello, I'm Dr. Kara. I have over 20 years of experience as a veterinarian and I'd like to help with your concerns about Melyn and his carsickness.
Cinnarizine is an antihistamine, calcium channel blocker. It is not a drug that we use routinely in dogs, and as such there isn't a published, recommended dose
Dogs are prone to car sickness as their sense of balance is much better than ours and as such they are easily affected by the motion of cars or boats. Some dogs do outgrow it, and he may given a little more time.
Try to keep trips short and as positive as possible. Some dogs get stressed if the only places they go are negative, such as a veterinary clinic. By making the destination enjoyable he may feel less stressed so less likely to get sick.
You can give Gravol also known as Dramamine (dimenhydranate) for carsickness. The dose is 2mg to 4mg per kilogram of body weight. Give it an hour two before travel. It will last about 8 hours. Side effects are mild sleepiness and dry mouth.
Or you can try Benadryl (diphenhydramine) at 0.5mg to 1mg per kilogram of body weight orally. Side effects are sedation and dry mouth as well. It should be given an hour or two before travel.
I do recommend that he not eat for 8 hours before travel if the car-ride will be long. Ice cubes can help to quell nausea too and keep him hydrated.
I also recommend keeping a window cracked as fresh air seems to help too.
Some dogs do better if they cannot see out of the car, the moving landscape seems to make them dizzier and thus more nauseous. Try and get him to lay down in the car, or use a carrier and put it on the floor of the car.
If these things don't work discuss a medication called Cerenia
(maropitant) with your veterinarian. It works very well and lasts at least 8 to 12 hours.
If you believe this is at all anxiety related you can try products such as Bach's Rescue Remedy. See this link for further information: http://www.bachflower.com/Pets.htm
If that isn't enough your veterinarian can prescribe anti-anxiety medications for him that may work better.
Please let me know if you have any further questions.