Although the efficacy of two pre-exposure prophylaxis (PrEP) regimens containing differing prodrug formulations of tenofovir are virtually identical, the balance between benefit and risk tips in favor of the combination using the older formulation, tenofovir disoproxil fumarate (TDF), a pharmacology researcher said.
An analysis of the pharmacologic profiles of TDF plus emtricitabine (FTC; Truvada and generic) with tenofovir alafenamide (TAF) plus FTC (Descovy) shows that the risk of decreased bone mineral density and renal toxicity with TDF are significantly lower than those of weight gain and related metabolic and cardiovascular problems associated with the newer tenofovir formulation TAF, according to pharmacology research fellow Andrew Hill, MD, PhD, from the University of Liverpool (England).
“I think when we’re comparing these two drugs overall, we have a clear benefit/risk, and we need to take both of these potential toxicities seriously, “ he said in an online presentation during IDWeek 2020, an annual scientific meeting on infectious diseases held virtually this year.
“But in my view, treating women – Black women – with TAF/FTC is a bad thing,” he continued. “I think it’s going lead to more harm, more myocardial infarctions, more cases of diabetes, and potentially more adverse birth outcomes, and I think that is a risk that is not worth taking, given that the apparent benefit in terms of bone mineral density and renal markers is a hypothesis at best, and is not translated into hard clinical endpoints.”
Adverse event profiles
Dr. Hill compared the side effect profiles of the two agents when used both in antiretroviral therapy (ART) in combination the integrase inhibitor dolutegravir (DTG; Tivicay), and in PrEP.
World Health Organization guidelines for first-line ART recommend the use of TDF/FTC/DTG, reserving TAF plus lamivudine (3TC) and DTG for use in special circumstances only, Dr. Hill noted.
He pointed to a pooled analysis of data from eight randomized, controlled trials of treatment-naive people living with HIV who started on ART from 2003 to 2015. The authors found that demographic factors associated with weight gain included lower CD4 cell counter, higher levels of HIV type 1 RNA, no injection drug use, female sex, and Black race.
They also found that, among nucleoside/nucleotide reverse transcriptase inhibitors, TAF was associated with more weight gain than TDF, abacavir, or zidovudine.
“This pattern is seen consistently across studies both of pre-exposure prophylaxis or treatment comparing tenofovir with either TAF or other nucleoside analogs,” he said.
The greater weight gain with TAF versus TDF was seen in both treatment trials and in the DISCOVER PrEP trial.
In addition, in a crossover trial conducted in Germany, patients who switched from TDF to TAF had an approximately 2 kg increase in body weight.
TAF has also been associated with higher grade 3 or 4 glucose and LDL cholesterol than TDF in clinical trials for the treatment of hepatitis B infections, and with higher LDL cholesterol and total cholesterol levels as well as diabetes in patients treated with the drugs in combination in the EMERALD HIV trial.
Clinical trials also tend to underestimate the real-world population of persons at highest risk for adverse events from TAF, Dr. Hill said, noting that the percentage of Black women in phase 3 trials for dolutegravir was 9%, compared with 42% among persons infected with HIV worldwide. The respective percentages for Black men are 16% versus 30%. These differences are similar across clinical trial programs for other ART agents.
“Generally, it’s women and Black people who seem to be at greatest risk for safety issues,” he said.
In the ADVANCE trial comparing TAF/FTC/DTG with TDF/FTC/DTG and a control arm of TDF, FTC and efavirenz, the mean change in weight among men after 3 years on the TAF-based regimen was a gain of 7.2 kg (15.9 lbs), compared with 5.5 kg (12 lbs) with TDF, and 2.6 kg (5.7 lbs) with the efavirenz-containing regimen.
In women enrolled in the same trial, the respective mean weight gains were 12.3 kg (27 lbs), 7.4 kg (16.3 lbs), and 5.5 kg (12 lbs).
“All of our analyses so far have shown that the weight continues to go up. We’re actually seeing people doubling in their body weight. We’ve seen some women come into clinic and their doctors don’t even recognize them because they’ve put on so much weight,” he said.
In women, most of the gain in weight occurs as limb or trunk fat, with a predominance of visceral fat.
People taking TAF in the trial were also at significantly greater risk for developing the metabolic syndrome, and at week 96, 27% of women on TAF/FTC/DTG had treatment-emergent obesity, compared with 17% for those on TDF/FTC/DTG and 11% for those on TDF/FTC/EFV. In men, the respective 96-week rates of treatment-emergent obesity were 7%, 3%, and 2%.
Clinical obesity itself is a risk factor for obstetric complications and birth outcomes, Alzheimer’s disease, type 2 diabetes, cardiovascular disease, hypertension and cancer, and an average 4-year reduction in life expectancy, Dr. Hill said. “I think it’s actually very unlikely that the [World Health Organization] guidelines will now change and allow the widespread use of TAF/FTC in combination with integrase inhibitors worldwide given these potential implications.”