Pharmacokinetics of Calcineurin & mTOR Inhibitors in HIV-1 Infected Kidney Transplant Recipients After Switch to BIC/FTC/TAF

Chronic kidney disease (CKD) is a critical comorbidity for patients living with HIV (PLWH), with an estimated prevalence between 2.4 and 17%, leading to end-stage renal disease 3 to 6 fold more than non-HIV population. However kidney transplantation for PLWH has become the first-line therapy for end-stage renal disease, with an enhanced survival benefit compared to remaining on dialysis.

Management of antiretroviral therapy (ART) in HIV-infected kidney transplant recipients (HIV-KTR) has historically been problematic because of the potential nephrotoxicity of some antiretroviral drugs and the interactions between calcineurin inhibitors, mTOR inhibitors, and ritonavir or cobicistat-boosted containing-ART. The use of tenofovir disoproxil fumarate (TDF), a widely recommended nucleotide analogue for the treatment of both HIV and HIV/hepatitis B virus (HBV) co-infection, is restricted in vulnerable kidney population as HIV-KTR due to its major potential toxicity consistent with tubular dysfunction and rarely with a progressive sustained decline in renal function. The optimal long-term ART regimen is not known in HIV-KTR, though it makes intuitive sense to avoid regimens containing TDF, given its potential nephrotoxicity. Nevertheless the potent virological efficacy of TDF both on HIV and HBV and its highest in-vitro barrier to resistance among the Nucleoside Reverse Transcriptase Inhibitors makes tenofovir use highly recommended or even essential in HIV/HBV co-infections.

Tenofovir alafenamide (TAF) and bictegravir (BIC) are 2 novel antiretroviral drug available in HIV treatment in combination with emtricitabine (F) (B/F/TAF):

• TAF is a novel prodrug of tenofovir that may offer improved renal safety over TDF. TAF is more stable in plasma and is metabolized intracellularly by cathepsin A, an enzyme that is highly expressed in lymphoid tissues. Therefore, TAF can achieve higher intracellular levels of the active moiety tenofovir diphosphate, with lower levels of circulating tenofovir when compared with TDF. This more targeted treatment could potentially result in fewer renal and bone complications despite the same clinical efficacy as TDF. TAF was approved for use in PLWH with mild-moderate CKD (eGFR: 30-69 mL/min).

The availability of TAF seems a potential addition to the antiretroviral armamentarium in HIV-KTR. * BIC is a novel second-generation integrase strand transfer inhibitor (INSTI) has a high in-vitro barrier to resistance and in-vitro activity against most INSTI-resistant variants and has low potential for clinically meaningful drug-drug interactions. BIC has been recently approved by the FDA, in coformulated B/F/TAF for the treatment of HIV-1 infection in antiretroviral naïve subjects and in those with suppressed viremia.

No data are available yet with TAF use in HIV-infected kidney transplant recipients as well as with BIC, especially about potential drug-to-drug interactions with immunosuppressive drugs such as calcineurin \& mTOR inhibitors.

At last simplification to a single tablet regimen (STR) may offer a once-daily option for HIV-KTR who have multiple comorbidities, often requires complex regimens with a high pill burden.