Sustiva and Prezista contain active ingredients that may potentially influence each other [1], thus shouldn’t be co-administered without close medical supervision.
Efavirenz, an active component of Sustiva, cuts off the activity of the reverse transcriptase enzyme, without which viral particles cannot divide and multiply. This drug does not cure HIV or AIDS, but it helps stop the infection of healthy cells in the body. Efavirenz is indicated for antiretroviral combination therapy for adults, adolescents, and children over 3 months old who are infected with HIV-1. This med is also prescribed to lower the risk of HIV infection when combined with other ARV drugs as a part of an extended prevention regimen for people at significant risk [2]. The drug should not be used as an independent medicine since the resistance of human immunodeficiency virus to the active substance is quickly developed.
Prezista (darunavir) is an inhibitor of the HIV-1 protease. The drug specifically inhibits the cleavage of the HIV Gag-Pol polyproteins in infected cells, stopping the formation of viable viral particles. The drug should be prescribed in combination with ritonavir in low dosages as a means of improving its pharmacokinetic characteristics as well as in coadministration with other antiretroviral medicines [3]. After initiation of Prezista therapy, patients should not change or discontinue treatment without consulting their healthcare provider.
Coadministration of darunavir with efavirenz may reduce the plasma concentrations of Prezista, even in the presence of ritonavir or another low-dose pharmacokinetic booster. Reduced darunavir plasma levels may lead to diminished virologic response and possible resistance to darunavir. It is caused by efavirenz induction of CYP450 3A4, the isoenzyme responsible for the metabolic clearance of darunavir and ritonavir. Caution is advised if a drug containing darunavir is coadministered with efavirenz. The response to ART should be monitored closely, and the dosage of both drugs should be adjusted if necessary [4].