Disposition of Single-Dose Intravenous and Oral Aspirin in Children

We described the pharmacokinetics of acetylsalicylic acid and salicylic acid in 5 children with prior Kawasaki disease receiving buffered aspirin tablets or intravenous aspirin DL-lysine. Oral aspirin is characterized by its longer mean residence time in the body (MRT), an indicator for duration of exposure, than intravenous aspirin (1.18 vs. 0.37 h). The apparent elimination half-life (t1/2) of acetylsalicylic acid was also longer after oral than after intravenous administration of aspirin (40 vs. 17 min). The mean absorption time was calculated to be as long as 0.8 h. In contrast, the two modes of administration gave virtually identical results regarding MRT of salicylic acid proper and its t1/2. After oral administration of aspirin, 51% of the dose is absorbed intact as acetylsalicylic acid while 23% is converted to salicylic acid presystemically, indicating that 74% of aspirin is actually absorbed. Our data suggest that an equivalent intravenous aspirin dose to achieve the same salicylic acid concentration is about 70% of the oral dose. However, the area under the curve of acetylsalicylic acid itself, a more potent cyclooxygenase inhibitor than salicylic acid, would be about 1.5 times higher than that following oral administration. The clinical consequences of this exposure difference remain uncertain.