Allergen Immunotherapy with Depigmented–Polymerised Cat Allergoid Is Safe and Well-Tolerated in Patients with Allergic Rhinitis/Rhinoconjunctivitis

Background/Objectives: For decades, only native allergen extracts with a high incidence of adverse drug reactions (ADRs) were available for allergen-specific immunotherapy (AIT)—generally administered subcutaneously—to treat allergy to feline epithelia. Modified allergen extracts are a promising alternative to reduce the number of ADRs. The purpose of this study was to collect data on the safety of a depigmented–polymerised cat allergoid under real-world conditions in clinical routine. Methods: This study was designed as a voluntary non-interventional post-authorisation safety study (NIS-PASS), specifically focusing on adverse events (AEs)—including ADRs—that occur upon injection and assessing the influence on quality of life (QoL). The observation period was the initial phase (up-dosing) of the AIT. Results: Of 101 included patients, 91 patients were treated with the depigmented–polymerised cat allergoid. Regardless of the age group, around 50% of patients reported ADRs, which were mainly delayed local reactions (LRs). Other ADRs occurred only sporadically without persistent patient impairment. The ADR incidence did not differ significantly between quick and conventional up-dosing regimens or between adult and adolescent patient groups. The QoL data revealed no significant changes in any domains of the SF-12 questionnaire during the 12-week observation period. Conclusions: Overall, subcutaneous allergen immunotherapy (SCIT) with the depigmented–polymerised cat allergoid is a well-tolerated and safe treatment option for patients with cat allergy.