Transient Platelet Elevation Following Oseltamivir Administration in Pediatric Chronic Immune Thrombocytopenia

Oseltamivir is widely used for influenza, but its effects on platelet counts in pediatric patients with chronic immune thrombocytopenia (cITP) remain unclear. We report three adolescents with cITP (four events) who showed transient platelet elevation after oseltamivir while receiving low-dose prednisolone and eltrombopag. Platelet counts increased nine to 14 days after oseltamivir initiation (median: 11.5 days), from a median of 9.1×10⁴/μL to 26.7×10⁴/μL; two events required eltrombopag dose reduction or temporary interruption. Platelet counts subsequently returned to approximately baseline within a median of 57 days, and no thrombosis, major bleeding, or other adverse events related to thrombocytosis were observed. Although causality cannot be established and influenza itself may contribute to platelet changes, clinicians should be aware that some children with cITP may develop transient platelet elevation after oseltamivir for influenza, which can complicate eltrombopag management and warrants planned platelet monitoring.