Why the carrier itself is the problem
Most cats do not fear the veterinarian nearly as much as they fear the box that predicts the veterinarian. A carrier that appears only on appointment days, smells of disinfectant and storage, and is followed by a chase around the sofa teaches a clear lesson: when the box comes out, hide. Training works by breaking that prediction. The carrier needs a long, boring life as furniture first, so that on the morning it is actually needed it is simply the place your cat already naps, and being closed inside it is a familiar event rather than the start of an ambush.
Make it part of the room
Put the carrier in a spot your cat already likes, door propped or removed entirely, with a blanket that smells of home inside. Feed treats in it, then whole meals just inside the entrance, then meals at the back, over days rather than in one determined afternoon. Spray or wipe products are optional extras; the heavy lifting is done by repetition and food. If your cat will only eat at the entrance for a week, that is the pace. A cat who chooses to walk in for breakfast has learned more than a cat who was placed inside and praised while planning his escape.
Practise the closing, the lift and the car
Once he naps in the carrier voluntarily, close the door for a few seconds, open it again and let him leave without ceremony. Build to a minute, then to being lifted and carried to another room and set down, always ending before he protests so the memory stored is the calm version. Next come car rehearsals with no destination: carrier secured in the car, engine on, a short sit, then back inside for a meal. A brief drive around the block, repeated on ordinary days, separates the car itself from the clinic at the end of the road.
Rehearse the appointment-day details
Load from the room where the carrier lives rather than chasing him into it, and keep voices low and movements unhurried, because cats read a tense household instantly. Cover the carrier with a light blanket in the car if visual stimulation winds him up, secure it so it cannot slide, and drive smoothly rather than apologising out loud the whole way. At the clinic, a familiar-smelling blanket inside gives him one home object in a strange-smelling room. Afterwards, let him leave the carrier at his own speed at home and offer food, so the story ends with release and dinner rather than lingering grievance.
When fear runs deeper than habit
Some cats, especially those with a frightening early trip or a long gap since their last outing, panic despite patient groundwork: drooling, open-mouth breathing, urinating in the carrier or frantic clawing at the door. Do not push through rehearsals with a cat at that level of distress. Talk to your veterinarian about his fear before the next appointment; they can advise on approaches suited to him and tell you what signs mean a trip should be rescheduled. Practising handling at home, such as brief paw touches and being lifted onto a table, also helps the examination itself feel less foreign.
Calm box, ready records
When trip day comes, KinsLe's Pet Passport means his vaccination history and health notes travel as one portable packet alongside the carrier, ready to hand over at reception.