Successful oral desensitization to temozolomide in a patient with immediate hypersensitivity reaction

Temozolomide (TMZ) is an oral alkylating agent that represents a cornerstone therapy for glioblastoma and other high-grade gliomas. Although TMZ is generally well tolerated, hypersensitivity reactions (HSRs), including urticaria, have rarely been reported and may lead to treatment interruption. Rapid drug desensitization (RDD) offers a potential strategy to enable continuation of essential therapy; however, standardized protocols for TMZ are limited. Here, we present a 46-year-old woman with glioblastoma who developed widespread urticaria during maintenance TMZ therapy. The reaction developed within four hours of the last dose and completely resolved following treatment with corticosteroids and antihistamines within 24 h. Based on clinical history and lesion characteristics, an immediate HSR to TMZ was considered. As no alternative treatment options were available, an oral RDD protocol targeting a dose of 240 mg was prepared. The protocol included stepwise dose escalation using diluted oral solutions followed by capsule administration, with premedication using cetirizine and methylprednisolone. Desensitization was successfully completed without breakthrough reactions, and the protocol was repeated in two consecutive cycles without complications. Our protocol provides detailed information on drug preparation, dose increments, and administration intervals, supporting its reproducibility and feasibility. This case contributes to the limited literature by demonstrating that oral RDD can be safely and effectively performed in patients with TMZ-induced urticaria. The successful repetition of desensitization further supports the safety of this approach. This protocol may assist clinicians in maintaining first-line TMZ therapy in patients with HSRs, thereby preventing unnecessary treatment interruptions and improving clinical outcomes.