Figure 1.

Target-mediated drug disposition (TMDD) with quasi-equilibrium (QSS) approximation. Base parameters are estimated for inflammatory bowel disease (IBD) and ankylosing spondylitis (AS), the latter being used as a reference, while TMDD parameters are estimated for central (below, “C” exponent) and peripheral (above, “P” exponent). In(t) is infliximab input function, V1 and V2 are central and peripheral volumes of distribution, respectively, CL and Q are endogenous and intercompartment clearances, respectively, R₀, k_in, and k_out are baseline TNF-α amount, zero-order unbound target production rate constant and first-order destruction rate constant, respectively, K_SS and k_int are steady-state dissociation constant and infliximab-TNF complex elimination rate constant, respectively.