TAF boosters do not affect tenofovir levels in urine

Patients with HIV on unboosted vs boosted, dose-reduced tenofovir alafenamide (TAF) medication show comparable urine levels of tenofovir (TFV), according to a study presented at the recently concluded 2021 International AIDS Society Conference on HIV Science (IAS 2021).

“TAF is increasingly used in HIV treatment, with or without agents that require pharmacologic boosters like ritonavir/cobicistat. Boosters increase TAF levels, so the TAF dose is lowered in single-pill combinations,” the researchers said. “We hypothesized that individuals on dose-adjusted boosted TAF would have similar urine TFV concentrations to those on unboosted TAF.”

The study included 45 participants who showed evidence of virologic suppression, as determined by having their most recent HIV RNA levels <200 copies/mL. Urine samples were collected and subjected to liquid chromatography/tandem mass spectrometry for the measurement of TFV levels. All participants showed daily adherence at two clinics.

Thirty of the participating patients with HIV were on unboosted TAF (25 mg daily), while the remaining 15 were taking boosted TAF: 12 were on reduced, 10-mg daily doses, while three were still taking 25-mg doses. Baseline demographic variables were comparable between arms, as were creatinine levels (1.1 vs 1.0 mg/dL). [IAS 2021, abstract PEB076]

Unadjusted univariate linear regression showed that a booster dose following TAF dose-reduction to 10 mg led to no significant change in urine TFV levels (geometric mean ratio [GMR], 1.07, 95 percent confidence interval [CI], 0.53–2.16).

Controlling for baseline confounders such as age, sex, weight, and creatinine concentrations did not meaningfully change the primary findings, further confirming that boosted 10-mg TAF did not result in significantly different urine TFV levels relative to unboosted 25-mg TAF (adjusted GMR, 1.10, 95 percent CI, 0.53–2.28; p=0.80).

Similarly, boosters had no significant impact on urinary TFV levels even without dose de-escalation (boosted vs unboosted 25-mg: adjusted GMR, 1.46, 95 percent CI, 0.41–5.12; p=0.55).

None of the baseline factors considered—creatinine, sex, age per 10 years, and natural log-transformed weight in kilograms—likewise had a significant impact on urinary TFV levels.

The present study found that using boosters to increase TAF levels in HIV treatment did not significantly impact downstream biomarker concentration in the urine. Notably, such effect remained true even without reducing the boosted TAF dose.

“These results have important implications for our forthcoming point-of-care urine immunoassay for TAF, implying that separate adherence cutoffs will not be necessary for patients on boosters and dose-reduced TAF,” the researchers said.

“A single point-of-care TAF immunoassay will thus support monitoring on most TAF-based antiretroviral therapy,” they added.