Safety Implications of Switching Pembrolizumab Dosage From 200 mg Every 3 Weeks to 400 mg Every 6 Weeks in Patients With Advanced NSCLC

Introduction Administration of 400 mg pembrolizumab every 6 weeks (400 mg Q6W) has been approved on the basis of the results of simulated pharmacokinetic modeling and exposure–response analyses. Nevertheless, the safety of switching dosage from 200 mg every 3 weeks (Q3W) to 400 mg Q6W during treatment remains unclear. Methods This study involved patients (N = 45) with advanced NSCLC, in whom the pembrolizumab dosage was switched from 200 mg Q3W to 400 mg Q6W between August 2020 and November 2021 in our institute. Results At the time of switching, the median age of the patients was 71 (range: 32–84) years, and 32 patients (71.1 %) were males. The median number of cycles of 200 mg Q3W before switching was six (range: 1–31). After switching, new or worsening immune-related adverse events (irAEs) occurred in 17 of the 45 patients (37.8%) within three cycles. The irAEs were pneumonitis in 11 patients (24.4%), diarrhea in three patients (6.7%), renal dysfunction in two patients (4.4%), adrenal dysfunction in two patients (4.4%), a skin rash in one patient (2.2%), fulminant type 1 diabetes mellitus in one patient (2.2%). Conclusions The switching of pembrolizumab dosage from 200 mg Q3W to 400 mg Q6W resulted in the occurrence of new or worsening irAEs, in particular, pneumonitis, in the early cycles even in patients who had received stable treatment with 200 mg Q3W.