Bioavailability of aspirin and salicylamide following oral co-administration in human volunteers.

BC powder (I) is a commercially available analgesic containing the active ingredients aspirin and salicylamide. The kinetics of I, BC powder minus aspirin (II), and BC powder minus salicylamide (III) were evaluated in 13 volunteers. Ten minutes after administration of I, aspirin reached a maximum concentration of 12.9 micrograms/mL, while salicylamide concentration reached a peak value of 3.4 micrograms/mL. However, when III was administered, aspirin was not detected at 10 min and only reached a concentration of 0.4 microgram/mL at 2 and 6 h. Furthermore, the area under the plasma concentration versus time curve for aspirin when III was administered was sixfold less compared with treatment with I. The area under the curve for aspirin metabolites was significantly different in I versus III. After treatment with II, a delay in salicylamide peak concentration was observed. Gentisamide was not detected throughout the study. This study demonstrates that salicylamide significantly enhances plasma levels of aspirin with potential therapeutic implications.