Explain why plasma concentration of drugs with enantiomers does not correlate with response.

Explain why plasma concentration of drugs with enantiomers does not correlate with response.

• A. Only one enantiomer is active
• B. The total includes both enantiomers, but only one is active
• C. Enantiomers are interchangeable
• D. Plasma concentration always correlates with effect

Answer: (B)

Enantiomers can differ in how strongly they produce a pharmacologic effect and in how they are processed by the body. The plasma concentration you measure typically reflects the sum of both enantiomers, but usually only one enantiomer is responsible for the therapeutic response. So a high total level may not translate to a strong effect if most of that drug is the inactive enantiomer. That’s why plasma concentration doesn’t reliably predict response unless you focus on the active enantiomer. The best description is that the total includes both enantiomers, but only one is active.

Enantiomers can differ in how strongly they produce a pharmacologic effect and in how they are processed by the body. The plasma concentration you measure typically reflects the sum of both enantiomers, but usually only one enantiomer is responsible for the therapeutic response. So a high total level may not translate to a strong effect if most of that drug is the inactive enantiomer. That’s why plasma concentration doesn’t reliably predict response unless you focus on the active enantiomer. The best description is that the total includes both enantiomers, but only one is active.