Summary: In treating HIV infection, strict adherence to drug therapy is crucial in maintaining a low viral load, but the high dosages required for this often have toxic side effects which make perfect adherence to antiretroviral therapy (ART) unsustainable. Moreover, even in the presence of drug therapy, ongoing viral replication can lead to the emergence of drug-resistant virus variances. We introduce a mathematical model that incorporates two viral strains, wild-type and drug-resistant, to theoretically and numerically investigate HIV pathogenesis during ART. A periodic model of bang-bang type is employed to estimate the drug efficacies. Furthermore, we numerically investigate the antiviral response and we characterize successful drugs or drug combination scenarios for both strains of the virus.