Schematic of the model. An HIV-infected cell type (xpre) that is susceptible to an antiretroviral targeting the step in the viral life cycle that proceeds at rate kHIV after which the infected cell is no longer susceptible to the antiretroviral drug (xpost). The drug-susceptible cell can be inhibited at rate kI to become an inhibited cell (xI), which can progress no further in the HIV viral life cycle. This inhibition may be reversed at a rate k-I. Cell types xpre and xI decay (e.g. through death of the cell or decay of the offending HIV virion) at rates δpre and δI, respectively.