Final answer:
For a cat that had an allergic reaction to vaccination, desensitization therapy is the recommended course of action, with careful monitoring afterward. Epinephrine may be administered in case of a severe reaction.
Step-by-step explanation:
When revaccination is necessary in a cat that has experienced an allergic reaction, desensitization therapy is recommended, followed by close observation of the patient for several hours. In the practice, desensitization therapy involves the administration of extremely dilute concentrations of allergens at prescribed intervals. The dosage is gradually increased to build up the cat's tolerance to the allergen. It is paramount to monitor the cat closely after the injection to manage any potential severe systemic reactions promptly. Emergency treatment for such reactions often includes an epinephrine injection, which can be life-saving by increasing blood pressure and relaxing bronchial smooth muscle, countering the effects of anaphylaxis.