FIG. 1.

Illustration of the parent metabolite model. All rifapentine (RFP) is assumed to be converted to the major metabolite (25-DRFP). N₁ represents the first hypothetical transit compartment up to N_n compartment. k_tr is the transit rate constant. k_a is the absorption rate constant from the hypothetical drug depot compartment to plasma. k (calculated as CL/V) is the elimination rate constant of rifapentine. CL_m is the time-varying metabolite clearance. V_m represents volume of distribution of the metabolite. k34 is the first-order rate constant of the metabolite from plasma to the peripheral compartment, and k43 is the first-order rate constant of the metabolite from the peripheral compartment back to plasma.