Takashi Nagao, MD,* Tsuneo Morishima, MD, PhD,* Hiroshi Kimura, MD, PhD,† Syumpei Yokota, MD, PhD,‡ Nobuko Yamashita, MD, PhD,* Takashi Ichiyama, MD, PhD,§ Mana Kurihara, MD, PhD,∥ Chiaki Miyazaki, MD, PhD,¶ Nobuhiko Okabe, MD, PhD # *Department of Pediatrics, Okayama University, Graduate School of Medicine and Dentistry, Okayama;†Department of Virology, Nagoya University Graduate School of Medicine, Nagoya;‡Department of Pediatrics, Yokohama City University, School of Medicine, Kanagawa;§Department of Pediatrics, Yamaguchi University School of Medicine;∥Department of Pediatrics, the Kanagawa Rehabilitation Center, Kanagawa;¶Fukuoka Center for Handicapped Children, Fukuoka; and#Infectious Diseases surveillance Center National Institute of Infectious Diseases, Tokyo, Japan Blood abnormalities, such as thrombocytopenia and elevated serum aspartate aminotransferase (AST), and brain computed tomography (CT) abnormalities are associated with poor outcome. Cyclooxygenase inhibitors, particularly aspirin, are known to cause Reye syndrome.[4,5] In Japan, cyclooxygenase inhibitors such as diclofenac sodium and mefenamic acid, but not aspirin, are widely used as antipyretic drugs in children. We found that some nonsalicylate antipyretic drugs, including diclofenac sodium and mefenamic acid, may be associated with the development of influenza-associated encephalopathy or may affect the severity of the disease. However, we were unable to thoroughly assess the relationship between the use of these medicines and prognosis.