This patient should continue his current antiretroviral regimen. Antiretroviral therapy for HIV usually comprises a “backbone” of two nucleoside/nucleotide reverse transcriptase inhibitors (NRTIs) plus a third agent, which may be a boosted protease inhibitor, a nonnucleoside reverse transcriptase inhibitor, or an integrase inhibitor. This patient's initial regimen contains the backbone of tenofovir and emtricitabine, primarily because these agents also have activity against hepatitis B. The third agent is elvitegravir, which is an integrase inhibitor; cobicistat is a cytochrome P-450 inhibitor used to boost the level of elvitegravir, which is metabolized through this pathway. This particular combination is available as a once-daily formulation, which is convenient for patients and encourages medication adherence. However, cobicistat also inhibits tubular secretion of creatinine, leading to increased levels of serum creatinine that do not reflect an actual change in the glomerular filtration rate (GFR). The creatinine level increases by an average of 0.14 mg/dL (12.4 µmol/L) with cobicistat. Because this does not actually affect the GFR, it is an expected occurrence and is not a reason to change the antiretroviral regimen, which is successful in this patient as demonstrated by the reduction in his viral load to undetectable levels. Investigation for true kidney dysfunction is recommended if the increase in creatinine level in patients taking cobicistat is 0.4 mg/dL (35.4 µmol/L) or more.

Changing the patient's antiretroviral regimen to an alternative NRTI backbone, such as abacavir-lamivudine or zidovudine-lamivudine, plus a third agent would be reasonable if a change in medications from his currently effective regimen were indicated, but this is not the case. Additionally, changing regimens from tenofovir and emtricitabine would lose the dual treatment effect of these agents for the patient's hepatitis B.

Even a brief discontinuation of antiretroviral therapy would be inappropriate because the patient is tolerating therapy well and it has been effective. Moreover, in this patient with chronic active hepatitis B, discontinuing agents with hepatitis B activity (tenofovir and emtricitabine) can lead to an acute flare in activity of the hepatitis, which can be severe.

Although this patient is at risk for several potential kidney diseases, including HIV-associated nephropathy, hepatitis B–associated kidney disease, and tenofovir renal toxicity, the likely artifactual increase in his serum creatinine level in combination with his negative urinalysis result and bland urine sediment does not suggest active kidney disease requiring further evaluation, such as by kidney biopsy.