Is My Cat’s Lethargy an Allergic Reaction?

A once playful kitten looses all energy after a routine vaccination.

Cat Expert Dr. Plotnick

Dear Dr. Plotnick,

I took my 2-year-old Siamese cat to the vet for his annual check-up. During the exam, he received his booster distemper shot. He has only been to the vet for his kitten shots and his neuter operation. About an hour after we bought him home, he started licking himself. Every time he licked a spot on the underside of his tail, about 2 inches from his anus, he became itchy, licked and bit at other spots on his body and ran away.
 
The rest of the night he was quiet, or he licked other spots and was fine. But as soon as he licked the spot on his tail, he ran away and hid. The next morning, I called the veterinarians office and they said it may be a reaction to the distemper vaccination. (He has had this shot as required as a kitten and never had any reaction.) They told us to give him a half of a 4 mg pill of Chlortrimeton, antihistamine, three times a day. We did this and it seemed to help the itching or hypersensitivity in the tail and he doesn’t lick and bite anymore. However, he has lost all his energy; he is completely lethargic when before he was a playful and active cat.

Could this be a side effect of the vaccine? We haven’t given him any more Chlortrimeton because we thought that may be affecting his behavior. (The itching isn’t as bad). Or could he be upset about the vet visit experience?

— Marie and Ed

Dear Marie and Ed,

The fact that this unusual licking behavior started about an hour after he received his vaccination certainly suggests that this is a reaction to the vaccine. Occasionally a vaccine will trigger an allergic reaction that can cause cats to itch. These reactions often diminish eventually; however, antihistamines usually accelerate the resolution of the clinical signs. In my experience, Benadryl is more effective for this than Chlortrimeton; however, both drugs are appropriate for this kind of reaction.

A more common adverse reaction to a vaccine would be lethargy, the kind that you’re describing. This usually resolves with no treatment after 24 or 48 hours, although occasionally a cat might require a little supportive care (force feeding, subcutaneous fluids) during this time. You didn’t mention in your letter how long this lethargic period has lasted. If it has been longer than 48 hours, then I suspect that this is not because of the vaccination. Whether theres an underlying illness or at 2 years old, your cats extended kittenhood has finally ended and he’s a quieter, more mature cat now is difficult to say.

Regards,
Arnold Plotnick, DVM

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