Snapshot A 55-year-old man presents to the HIV clinic for a follow-up visit. He was recently diagnosed with HIV and was started on first-line highly active antiretroviral therapy (HAART). However, his CD4 count at his last visit remained low. Drug resistance analysis of the HIV strain was sent at that time and revealed 3 major mutations causing the virus to be resistant to many first-line agents. The analysis also revealed that the HIV strain was CCR5-tropic. The patient was started on maraviroc. Introduction Drugs enfuvirtide prevents penetration of HIV into CD4+ T-cells maraviroc prevents attachment of HIV into CD4+ T-cells Clinical use a class of highly active antiretroviral therapy (HAART) often used as second-line in patients with drug resistance to first-line agents Enfuvirtide Mechanism of action binds to gp41, which inhibits HIV entry into the cell Adverse effects injection site skin reaction gastrointestinal upset fatigue Maraviroc Mechanism of action binds to CCR5, which is a protein on the surface of T-cells and monocytes inhibits the interaction of CCR5 with gp120 on HIV, thus inhibiting docking Clinical use requires assay showing that the virus is CCR5-tropic, which indicates that the virus is infecting cells with CCR5 expression (vs CXCR4), making it susceptible to the drug Adverse effects rash gastrointestinal upset immunosuppression