Ibuprofen levels in serum and synovial fluid.

Ibuprofen levels were measured in the serum and synovial fluid of 33 children (mean age 11 years) with juvenile chronic arthritis. A total daily dose of about 40 mg of ibuprofen per kg of body weight (mean 37.1 mg/kg) was given in three portions. In serum the peak level was reached 1-2 hours after drug intake. The half-life of elimination in serum was 2.3 +/- 0.5 hours (mean +/- 1 S.D., n = 12). Twelve hours after the last dose the mean serum level was about 20 micromol/l. Ibuprofen concentrations fluctuated far less in synovial fluid than in serum. In synovial fluid peak levels (mean 65 micromol/l) were reached 5-6 hours after drug intake. Thereafter, the levels declined slowly but 12 hours later were still higher than in serum.