My Cat Is Having An Allergic Reaction To A Thyroid

my cat is having an allergic reaction to a thyroid med she was on. she saw doctor Tuesday, was given buprenex injection, dexamethasone sp injection and 1 dose of convenia. to best of my knowledge dose was give Tuesday approximately 6 pm. she was kept with vet overnight; she came home yesterday evening. she has a lot of white fur and her skin is quite pink, I can see her ears and belly pink. is it o.k. to give her 1/2 tab of 4 mg chlor-trimeton tonight until I speak with her vet tomorrow morning. she is no longer taking methimazole; her last dose was sunday evening.