The association between acetaminophen concentrations in the cerebrospinal fluid and temperature decline in febrile infants.

The objective of this study consisting of a prospective cohort of febrile infants was to describe the correlation between cerebrospinal fluid (CSF) acetaminophen (paracetamol) concentrations and changes in body temperature in febrile infants. Infants, one week to one year of age, with rectal temperature >or=38.0 degrees C, treated with acetaminophen were studied if they underwent a lumbar puncture (LP). Patients received 15 mg/kg of acetaminophen 30 minutes to 4 hours before lumbar puncture was performed. Rectal temperature was documented before acetaminophen administration and at the time of lumbar puncture. Plasma and CSF acetaminophen levels were determined using high-pressure liquid chromatography. Thirty-one infants were studied. In a nonlinear regression, the relationship among acetaminophen concentrations in the CSF, time, and temperature differences is best described by a Lorentzian distribution. The model suggests that a peak effect on temperature is achieved at CSF concentration of 11.9 microg/mL and 182 minutes after acetaminophen administration (P<0.001 and P<0.001, respectively r=0.9 adjusted r square=0.78). Temperature decrement in young febrile infants, treated with acetaminophen, correlates with time and acetaminophen concentrations in the CSF. High concentrations of acetaminophen in the CSF, exceeding a certain level, are not associated with greater temperature decrement.