Which stereoisomer of ibuprofen is active, and how does it work?

The active stereoisomer of ibuprofen is S-ibuprofen, which is primarily responsible for its anti-inflammatory and analgesic effects. While R-ibuprofen is not active itself, it can be converted into S-ibuprofen in the body through metabolic processes. This conversion is significant because the S-enantiomer is the one that provides the therapeutic effects.

In this context, approximately 60% of R-ibuprofen can be converted to S-ibuprofen, which means that R-ibuprofen serves as a reservoir for the active form. This enzymatic conversion highlights the importance of both stereoisomers in the pharmacokinetics of the medication. Thus, when taken, R-ibuprofen contributes to the overall activity of ibuprofen through its conversion, allowing for more effective pain and inflammation management when S-ibuprofen is produced and utilized.

The other options present misunderstandings regarding the role of the stereoisomers. The mention of COX1 or COX2 needs to specifically relate to the mechanism by which S-ibuprofen provides relief by inhibiting the cyclooxygenase enzymes involved in prostaglandin synthesis, leading to reduced inflammation and pain.