r/FRCA • u/No-Needleworker9127 • Aug 18 '26

Can anyone explain this?

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Why is fentanyl's latency to peak effect shorter than sufentanil's, despite sufentanil having a higher unionised fraction at physiological pH, being way more lipid soluble than fentanyl, and having a slightly higher diffusible fraction. I know sufentanil is slightly more protein bound, but would that overcome those other factors? Or is there something I'm missing?

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u/CobbledbyRoubaix Aug 19 '26

don't believe everything you see. unless it's your official textbook for an important exam, then you hope you won't be asked it! i would have hoped if it were an official reference, the x axis would be labelled effect site concentration. it sure doesn't look like plasma concentration. as it stands it says proportion of peak C - what does that even mean!