Effect of CYP3A induction and inhibition on intravenous alfentanil (d0-ALF) plasma concentrations. Subjects received nothing (controls, ●), rifampin (▲), grapefruit juice (■), or ketoconazole (▼). Results are shown as mean ± SD (n=6); some SD are omitted for clarity. The d0-ALF dose was 1.0 mg, except after ketoconazole pretreatment (0.5 mg d0-ALF). Panels A–C show measured concentrations, and panels D–F show dose-adjusted concentrations. Panels A and D show results for sequential IV d0-ALF and oral d3-ALF (separated by 3 hr) administration, panels B and E show results for simultaneous IV d0-ALF and oral d3-ALF administration, and panels C and E show the results superimposed (solid lines and symbols, and open symbols and dotted lines represent sequential and simultaneous dosing, respectively).