A multicenter, placebo-controlled, double-dummy, randomized, parallel-group, double-blind study was conducted to verify the hypothesis of noninferiority for single-dose administration of zaltoprofen 160 mg, a nonsteroidal anti-inflammatory drug, compared with loxoprofen sodium 60 mg (loxoprofen), in terms of antipyretic and analgesic effects in patients with acute upper respiratory tract infection. The eligible 330 patients were assigned to one of 3 groups: zaltoprofen 160 mg, loxoprofen 60 mg and placebo. The analysis set consisted of 322 patients. Antipyretic effects were assessed by measuring body temperature, and analgesic effects were evaluated using a visual analog scale (VAS) for 4 h under the control of study staff. A detection kit for influenza virus A and B antigens was used to determine the presence of influenza virus infection. Compared with immediately before administration and with the placebo group, significant decreases in body temperature and summary VAS pain scores were noted in both the zaltoprofen and loxoprofen groups at 4 h after drug administration. Based on the degree of decrease in body temperature and the summary VAS pain scores up to 4 h after administration, noninferiority in terms of antipyretic and analgesic effects of zaltoprofen compared with those of loxoprofen was confirmed after single administration. Similar antipyretic and analgesic effects were also confirmed in influenza virus antigen-positive patients (73 patients). No clinical concerns were identified regarding safety. Zaltoprofen and loxoprofen are confirmed to be safe and useful for patients with acute upper respiratory tract infection, including those with influenza infection.