Effect of recent antipyretic use on measured fever in the pediatric emergency department

OBJECTIVES: To determine the prevalence of recent antipyretic use among febrile infants at a pediatric emergency department (ED) and to test the hypothesis that recent antipyretic use is associated with lower measured temperatures in the ED. METHODS: We prospectively enrolled infants younger than 366 days at a pediatric ED. Eligible subjects had a history of fever prior to arrival at the ED or had a measured temperature of 38 degrees C or higher at the ED. Research assistants collected detailed information about recent use of antipyretic drugs. Peak measured temperature prior to arrival at the ED (temperature maximum [Tmax]), measured temperature at the ED, defervescence from Tmax to measured ED temperature, and rates of diagnostic testing were compared between subjects who had or had not been treated with antipyretic medication within the past 6 hours. RESULTS: We enrolled 474 infants. Infants treated with an antipyretic medication (n = 187) had a significantly higher Tmax and a significantly higher measured ED temperature than untreated subjects (n = 287) (P<.001). Treated and untreated subjects did not differ in the amount of defervescence from Tmax to measured ED temperature (P = .41) unless treated subjects included only those who reportedly received therapeutic doses of antipyretic medication within 1 to 5 hours prior to arrival at the ED (P = .02). CONCLUSIONS: Although many febrile infants seen in the pediatric ED have recently received antipyretics, only a few have received a therapeutic dose between 1 and 5 hours prior to arrival. Among febrile infants seen in the ED, recent antipyretic use is associated both with a higher reported Tmax and with higher measured temperatures at the ED. Patients treated with a therapeutic antipyretic dose 1 to 5 hours prior to arrival experience more defervescence from their Tmax than untreated subjects.