Case Report: A case of carbapenem hypersensitivity and tigecycline-associated coagulopathy after immunotherapy for advanced oral cancer.

Background: Managing complex infections after immunotherapy in patients with advanced head and neck cancer is clinically challenging, especially when severe adverse drug reactions like carbapenem hypersensitivity and tigecycline-associated coagulopathy further limit treatment options. This case demonstrates the potential contribution of clinical pharmacists in such difficult scenarios. Case presentation: A 74-year-old man with oral squamous cell carcinoma developed severe sepsis after one cycle of PD-1 inhibitor (penpulimab) plus EGFR inhibitor (cetuximab). The clinical pharmacist sequentially recommended escalation to meropenem, switch to piperacillin-tazobactam, and addition of vancomycin. Later, the pharmacist recognized possible imipenem-related central nervous system effects, leading to discontinuation of all carbapenems due to possible cross-hypersensitivity. Subsequently, tigecycline was initiated, its associated coagulopathy was managed, and a switch to doxycycline was made. Results: The patient's fever resolved, and coagulation substantially improved; the infection was finally controlled. Causality was assessed using the Naranjo scale (imipenem 7, meropenem 5) and the RUCAM scale (penpulimab 6). Conclusion: In this case, the clinical pharmacist's dynamic assessment and use of quantitative adverse reaction tools (Naranjo and RUCAM scales) contributed to successful infection control and management of drug toxicity.