Fig. 1.
Final structural model. Efavirenz is absorbed through three transit compartments into the liver compartment, based on four identical first-order rate constants. For the first pass through the liver, a fraction of the efavirenz amount is extracted and cleared, and the fraction of the amount remaining reaches the systemic circulation and becomes available for redistribution into the peripheral compartment. Efavirenz recirculates from the central compartment to the liver with a flow equivalent to liver plasma flow, and at each pass the liver extracts a further fraction. ktr first-order rate constant, Eh fraction of efavirenz extracted, Qh liver plasma flow, N number of transit compartments, CLh hepatic clearance, Q intercompartmental clearance, Vh, Vc and Vp volume of ditribution of the liver, central and peripheral compartments, respectively