Some pets become more anxious when a tranquilizer begins to take effect. An unusual reaction to tranquilizers can make a pet agitated and excitable. It may help to do a 'test run' by giving a dose of the medication a few days before travel so you can observe its effects on your pet. Take frequent short trips with your cat. Place your cat in a carrier with a soft blanket so it can feel more secure.
Cats are more confident and comforted in a confined area.
A carrier will also help to prevent injury should they decide to race around the inside of your vehicle and will also prevent you from being unnecessarily distracted.