Bictegravir (formerly GS-9883) is a potent integrase inhibitor under development for the treatment of people with HIV. Bictegravir is made by Gilead Sciences.

In laboratory experiments with cells and HIV, bictegravir can work against many strains of HIV that are resistant to other integrase inhibitors, such as raltegravir (Isentress) and elvitegravir (in Genvoya and Stribild). Bictegravir is also effective against some strains of HIV that are resistant to another integrase inhibitor, dolutegravir (Tivicay and in Triumeq).

In a phase II randomized clinical trial, researchers gave 131 people who had not previously used HIV therapy bictegravir or dolutegravir, each drug taken with a backbone of TAF (tenofovir alafenamide) and FTC (emtricitabine). Both bictegravir- and dolutegravir-containing regimens performed well over 48 weeks, with more than 90% of participants achieving a viral load less than 50 copies/mL. Side effects were common but were mostly mild or moderate. No side effects were graded as serious and no one died in the study.

Bictegravir, which will be co-formulated (put into one pill) with TAF and FTC, can be taken once daily. Phase III clinical trials are underway with the bictegravir-containing combination and results should be available in the second half of 2017. A trial with about 470 HIV-positive women using a bictegravir-containing regimen is planned for later in 2017.

Study details

Researchers in the U.S. randomly assigned participants in a 2:1 ratio to receive the following:

• bictegravir (75 mg) + TAF + FTC – 65 participants
• dolutegravir + TAF + FTC – 33 participants

Participants could take the study medicines with or without food, once daily. Several doses of bictegravir have been assessed in earlier studies and as a result of these studies Gilead scientists have decided that the 75-mg daily dose is best.

The average profile of participants in the study was as follows:

• men – 96%, women – 4%
• age – 31 years
• 94% of participants were free from symptoms related to HIV disease
• viral load – 25,000 copies/mL
• CD4+ count – 444 cells/mm³
• estimated glomerular filtration rate (eGFR; a measure of kidney health) – 125 mL/minute

The study lasted for 48 weeks.

Results—Changes in viral load

Regimens based on integrase inhibitors can quickly drive down viral load in the blood and the drugs used in this study were no exception.

Week 12

By the 12^th week of the study, 94% of all participants had a viral load less than 50 copies/mL in their blood samples.

Week 24

By the 24^th week of the study, small differences in the proportion of participants who were virologically suppressed emerged as follows:

• bictegravir-based regimen – 97% had a viral load less than 50 copies/mL
• dolutegravir-based regimen – 94% had a viral load less than 50 copies/mL

Week 48

By the 48^th week of the study, the distribution of participants with suppressed viral loads was as follows:

• bictegravir-based regimen – 97% had a viral load less than 50 copies/mL
• dolutegravir-based regimen – 91% had a viral load less than 50 copies/mL

None of these differences in viral loads was statistically significant.

A closer look

Using a more sensitive viral load assay with a lower limit of 20 copies/mL, the distribution of suppressed viral loads at week 48 was as follows:

• bictegravir-based regimen – 91% had a viral load less than 20 copies/mL
• dolutegravir-based regimen – 88% had a viral load less than 20 copies/mL

This difference in viral loads was not statistically significant.

According to the study team, adherence among a minority of dolutegravir users was less than ideal. This may have affected the results.

Changes in CD4+ cell counts

On average, participants taking bictegravir had 258 more CD4+ cells by the end of the study and dolutegravir users had 192 more CD4+ cells. This difference was not statistically significant.

Side effects

Overall, side effects were distributed as follows:

• bictegravir-based regimen – 85% developed side effects
• dolutegravir-based regimen – 65% developed side effects

The distribution of specific side effects was as follows:

Diarrhea

• bictegravir-based regimen – 12%
• dolutegravir-based regimen – 12%

Nausea

• bictegravir-based regimen – 8%
• dolutegravir-based regimen – 12%

Bone pain

• bictegravir-based regimen – 6%
• dolutegravir-based regimen – 6%

Fatigue

• bictegravir-based regimen – 6%
• dolutegravir-based regimen – 6%

Liver enzymes

In general, neither regimen was associated with any signals of toxicity to major organ-systems. However, temporarily elevated liver enzyme (ALT, AST) levels in the blood seemed more likely to occur among a minority of bictegravir users—between 6% (ALT) and 9% (AST). The reasons for this are not clear. In one case the researchers underscored that a participant had recently become infected with hepatitis C virus and also drank excessive amounts of alcohol. Both of these factors cause liver injury and inflammation and would increase liver enzyme levels in the blood. As for all the other participants with temporarily elevated liver enzymes, as this was a relatively small study, some of those findings could have occurred by chance.

Creatine kinase

Elevated levels of the enzyme creatine kinase (also called creatine phosphokinase) were found in the blood of 13% of participants who were taking bictegravir and 9% of those taking dolutegravir. These elevations were temporary.

Elevated levels of these enzymes can occur in cases of muscle inflammation and injury. For example, if a blood sample was drawn after lifting weights or engaging in resistance exercises, levels of creatine kinase would be temporarily elevated. Other researchers have documented persistently elevated creatine kinase levels in a very small proportion of patients who were experiencing muscle injury arising as a side effect of the integrase inhibitor raltegravir (Isentress). However, in the present clinical trial, researchers did not think that the temporarily increased levels of creatine kinase were a consequence of drug side effects from bictegravir or dolutegravir, which have chemical structures somewhat similar to raltegravir.

Bear in mind

This is a small phase II clinical trial. As a result, firm conclusions about which regimen is better cannot be drawn. Phase II studies are designed to find preliminary evidence of safety and effectiveness that can then be explored in a trial of a more robust statistical design, such as a randomized phase III study. Phase III clinical trials are underway to assess bictegravir’s potential against dolutegravir and other anti-HIV drugs. The results from these studies should become available in the latter half of 2017. Bictegravir is also being tested in treatment-experienced patients and a trial to better assess bictegravir’s safety in women is being considered by Gilead.

—Sean R. Hosein

REFERENCES:

1. Sax PE, DeJesus E, Crofoot G, et al. Randomized trial of bictegravir or dolutegravir with FTC/TAF for initial HIV therapy. Conference on Retroviruses and Opportunistic Infections. 13-16 February 2017, Seattle. Abstract 41.
2. Lee FJ, Amin J, Bloch M et al. Skeletal muscle toxicity associated with raltegravir-based combination antiretroviral therapy in HIV-infected adults. Journal of Acquired Immune Deficiency Syndromes. 2013 Apr 15;62(5):525-33.
3. Calza L, Danese I, Colangeli V, et al. Skeletal muscle toxicity in HIV-1-infected patients treated with a raltegravir-containing antiretroviral therapy: a cohort study. AIDS Research and Human Retroviruses. 2014 Dec;30(12):1162-9.