Integrase inhibitors are a class of antiretroviral drugs that block HIV from inserting its genetic material into a human cell’s DNA. They do this by targeting a viral enzyme called integrase, which the virus needs to permanently embed itself inside the cells it infects. Since the first integrase inhibitor reached the market in 2007, the class has become a cornerstone of HIV treatment, recommended in most first-line regimens worldwide because of fast viral suppression, relatively few drug interactions, and generally good tolerability.
Why Integrase Matters to HIV
HIV cannot reproduce on its own. After the virus enters a human immune cell, it converts its RNA genome into DNA using another enzyme called reverse transcriptase. But that freshly made viral DNA is useless floating around in the cell’s cytoplasm. To hijack the cell’s own machinery and churn out new copies of itself, the virus needs to stitch its DNA into the cell’s chromosomes. That stitching job belongs to integrase.
Integrase catalyzes what researchers call “concerted integration,” meaning it splices both ends of the viral DNA into the host chromosome in a coordinated reaction, establishing a permanent infection in the target cell.1PubMed Central. Retroviral integrase: Structure, mechanism, and inhibition Once integrated, the viral DNA (now called a provirus) becomes a permanent part of the cell’s genome. The cell reads it like any other gene, producing new viral proteins and RNA that assemble into fresh virus particles. This is why HIV infection is lifelong: even if drugs stop the virus from replicating in the bloodstream, proviral DNA persists in long-lived cells.
The Two-Step Reaction Integrase Performs
Integrase works in two distinct chemical steps. First, in a reaction called 3′ processing, the enzyme trims a short stretch of nucleotides from each end of the viral DNA, exposing reactive chemical groups.2PubMed Central. 3′-processing and strand transfer catalysed by retroviral integrase in crystallo Second, in the strand transfer step, integrase uses those exposed ends to cut the host cell’s chromosome and simultaneously join the viral DNA to it.3PubMed. Retroviral Integrase Structure and DNA Recombination Mechanism The result is viral DNA covalently bonded into the host genome. The cell’s own DNA repair enzymes then clean up the small gaps left at the junctions.
Both steps happen within a large molecular assembly called an intasome, a complex of multiple integrase proteins bound to the ends of the viral DNA. High-resolution imaging has revealed that HIV’s intasome uses a core team of four integrase molecules working together.4PubMed Central. Cryo-EM structures and atomic model of the HIV-1 strand transfer complex intasome Understanding the shape of this complex has been crucial for designing drugs that jam into the right spot.
How Integrase Inhibitors Block Strand Transfer
The drugs in clinical use today are technically called integrase strand transfer inhibitors, or INSTIs. The name is precise: they specifically block the second step of the reaction, the strand transfer, rather than the initial trimming step. After integrase has already processed the viral DNA ends, an INSTI slips into the enzyme’s active site and binds to the two magnesium ions that integrase needs to do its chemistry. By grabbing hold of those metal ions, the drug physically displaces the processed viral DNA end, pushing it out of position so it can no longer attack the host chromosome.5Iranian Journal of Pharmaceutical Research. Progress in HIV-1 Integrase Inhibitors: A Review of their Chemical Structure Diversity The viral DNA is left dangling, unable to complete the splice, and the integration attempt fails.
This is a clever point of attack. By the time the drug acts, integrase has already committed to the reaction and processed the viral DNA. There is no going back. The virus cannot simply try again with unprocessed DNA because the trimming has already happened. The drug essentially catches the enzyme mid-stride.
The Five Approved Drugs
Five INSTIs have reached the market since 2007: raltegravir, elvitegravir, dolutegravir, bictegravir, and cabotegravir.6PubMed Central. HIV-1 Integrase Inhibitors: A Comparative Review of Efficacy and Safety They are often grouped into two generations based on how well they hold up against viral resistance.
Raltegravir and elvitegravir are considered first-generation drugs. Both are effective, but the virus can develop resistance to them through a relatively small number of mutations. Raltegravir requires twice-daily dosing (though a once-daily formulation exists), and elvitegravir needs a pharmacokinetic booster to maintain adequate blood levels. These features, combined with their lower resistance barrier, mean they are used less often in new prescriptions today.
Dolutegravir and bictegravir are second-generation drugs and have largely taken over. They have a higher barrier to resistance, meaning the virus has a harder time evolving around them. Structural studies have shown that second-generation compounds have expanded chemical scaffolds that interact with the protein backbone of integrase in ways that maintain effectiveness even when common resistance mutations are present.7PubMed Central. Structural basis of second-generation HIV integrase inhibitor action and viral resistance Both are taken once daily, do not need a booster, and are available in single-tablet regimens that combine the INSTI with other antiretrovirals.
Cabotegravir is the newest and has a unique role: it is available as a long-acting injectable, not just as a pill. More on that below.
How Quickly They Work
One of the practical advantages of INSTIs is speed. In a real-world clinical setting, people starting INSTI-based regimens reached undetectable viral loads in a median of about 60 days, compared to roughly 137 days on older NNRTI-based regimens and 147 days on protease-inhibitor-based regimens.8PubMed Central. Integrase inhibitor-based regimens result in more rapid virologic suppression rates among treatment-naïve human immunodeficiency virus–infected patients compared to non-nucleoside and protease inhibitor–based regimens in a real-world clinical setting That faster suppression matters: the sooner the virus becomes undetectable, the sooner a person is no longer at risk of transmitting it sexually, and the sooner their immune system can start recovering.
The picture is not perfectly clean across every study population, though. A large UK cohort found that after adjusting for multiple variables, people who started INSTIs actually had a somewhat higher rate of virological failure compared to those who started NNRTIs.9PubMed Central. First-line HIV treatment outcomes following the introduction of integrase inhibitors in UK guidelines The reasons likely have to do with the characteristics of the populations prescribed each drug class in that setting rather than the drugs themselves being less potent. INSTIs tend to be prescribed to people with more complex clinical situations. The broader body of trial data still supports INSTIs as among the most effective options for first-line treatment, which is why guidelines worldwide list them in that role.
Long-Acting Injections
Cabotegravir has changed what HIV treatment and prevention can look like. As a long-acting injectable, it is given as an intramuscular shot, and its elimination half-life is roughly 40 days, allowing administration on a monthly or every-two-month schedule.10PubMed Central. Formulation and pharmacology of long-acting cabotegravir For treatment, it is paired with a long-acting injection of rilpivirine (a different class of drug), and the combination is given every one or two months. For prevention (pre-exposure prophylaxis, or PrEP), cabotegravir is given alone every two months.
For people who struggle with daily pills, whether because of stigma, housing instability, mental health conditions, or simply preference, an injection every few weeks is a practical game-changer. But the long half-life introduces a complication on the back end. After the last injection, the drug lingers in the body for weeks at declining levels. If a person with HIV stops their injections without switching to oral treatment, the virus could encounter drug concentrations too low to suppress it but high enough to encourage resistance. Guidelines recommend bridging to oral therapy after discontinuation for this reason.11PubMed Central. A new paradigm for antiretroviral delivery: long-acting cabotegravir and rilpivirine for the treatment and prevention of HIV
Weight Gain
One side effect that has received growing attention is weight gain. People on INSTI-based regimens tend to gain more weight than those on other antiretroviral classes, and the difference is not trivial. In one study, people who switched to an INSTI-based regimen gained an average of about 2.5 kilograms over two years, compared to roughly 1.1 kilograms in a control group staying on non-INSTI regimens.12PubMed Central. The effect of a treatment switch to integrase Strand transfer inhibitor-based regimens on weight gain and other metabolic syndrome-related conditions That extra kilogram and a half may sound modest, but across large populations and longer time frames, it adds up, and it raises concerns about downstream risks like diabetes and cardiovascular disease.
The weight gain appears to affect some groups more than others. Women and people of African descent seem to be at higher risk, and dolutegravir has been singled out more often than other INSTIs in earlier analyses.13PubMed Central. Weight Gain and Integrase Inhibitors More recent data suggest bictegravir may actually be associated with a higher proportion of people experiencing weight gain: in one cross-sectional study, about three-quarters of people on bictegravir gained weight after a year of treatment, compared to about half of those on dolutegravir and less than a third on non-INSTI regimens.14Scientific Reports. Associations between weight gain, integrase inhibitors antiretroviral agents, and gut microbiome in people living with HIV: a cross-sectional study Researchers are actively investigating whether changes in gut bacteria might play a role, but the underlying mechanism remains unclear. It is worth noting that some weight gain after starting effective HIV treatment is expected and healthy, since suppressing the virus allows the body to recover. The concern is specifically about excess weight gain beyond that recovery effect.
Neuropsychiatric Side Effects
Insomnia and sleep disturbances are the most commonly reported neuropsychiatric symptoms with INSTIs, particularly dolutegravir. The spectrum also includes dizziness, anxiety, difficulty concentrating, and headache. In large cohort studies, around 3.5% of people on dolutegravir discontinued the drug because of neuropsychiatric side effects, with rates ranging from about 1.4% to 7.2% across different cohorts.15PubMed. Neuropsychiatric Adverse Events with Dolutegravir and Other Integrase Strand Transfer Inhibitors Those rates are higher than what was seen in the controlled clinical trials that led to approval, and higher than discontinuation rates for elvitegravir or raltegravir. Older people and women appear to be more vulnerable in some studies.
In children and adolescents, a secondary analysis of a large trial found a somewhat concerning signal: more young people in the dolutegravir group reported suicidal thoughts than in the comparison group, though most reports were transient, and overall rates of neuropsychiatric adverse events did not differ significantly between the two arms.16PubMed. Neuropsychiatric manifestations and sleep disturbances with dolutegravir-based antiretroviral therapy versus standard of care in children and adolescents: a secondary analysis of the ODYSSEY trial The numbers were small, making it hard to draw definitive conclusions, but they have prompted clinicians to keep an eye on mental health in younger patients starting these drugs.
The Dolutegravir and Pregnancy Story
In 2018, a surveillance study in Botswana flagged a possible link between dolutegravir use around conception and neural tube defects in newborns. Among over 1,600 deliveries to women taking dolutegravir at conception, five neural tube defects were found, a rate of about 0.3%. That was higher than the rate seen with other antiretrovirals or in HIV-negative women (roughly 0.1% or lower).17PubMed Central. Neural-Tube Defects and Antiretroviral Treatment Regimens in Botswana The finding triggered worldwide concern and led some countries to temporarily recommend avoiding dolutegravir in women of childbearing potential.
Subsequent, larger studies have been more reassuring. A U.S. national cohort study looking at millions of births found no significant difference in neural tube defect risk between infants exposed to dolutegravir around conception and those exposed to other antiretrovirals.18PubMed Central. Dolutegravir and pregnancy outcomes including neural tube defects in the USA during 2008–20: a national cohort study Updated data from the Botswana surveillance program itself, with more births enrolled, also showed the risk declining as numbers grew. Most guidelines now support the use of dolutegravir in pregnancy and in women who could become pregnant, reflecting the current evidence that the initial signal was likely a statistical fluctuation in a small sample rather than a true causal effect. The episode illustrates how a single early finding can reshape global health policy, and how accumulating data can eventually provide clarity.
Resistance and Its Limits
No antiretroviral is immune to resistance. HIV mutates rapidly, and under drug pressure, variants carrying mutations in the integrase gene can emerge. The mutations that matter most for INSTIs cluster around a few positions in the integrase protein, particularly at residues 148, 140, and 138. Combinations of mutations at these sites can reduce the effectiveness of dolutegravir and other second-generation INSTIs.19PubMed Central. Mechanisms of HIV-1 integrase resistance to dolutegravir and potent inhibition of drug-resistant variants
That said, resistance to second-generation INSTIs in practice remains rare, especially when the drugs are taken consistently. In clinical trials and cohort studies, treatment failure with emergent INSTI resistance has been an uncommon event for dolutegravir and bictegravir. The virus generally needs to accumulate multiple mutations to escape these drugs, and each mutation tends to come with a fitness cost, making the virus replicate less efficiently. First-generation drugs like raltegravir and elvitegravir are more vulnerable: a single primary mutation can significantly reduce their effectiveness. This is the main reason second-generation drugs have displaced the earlier ones in most guidelines.
Where HIV Inserts Itself and Why That Matters
Integrase does not insert viral DNA randomly into the chromosome. HIV has a strong preference for splicing into active genes, regions of the genome that the cell is actively reading. This preference is guided by a host cell protein called LEDGF/p75, which acts as a tethering factor. LEDGF/p75 binds to both chromatin and the viral integration machinery, physically steering the virus toward transcriptionally active regions.20PubMed Central. LEDGF/p75 functions downstream from preintegration complex formation to effect gene-specific HIV-1 integration. When researchers depleted LEDGF/p75 in cell experiments, HIV lost its preference for active genes and instead inserted more often near gene promoters and other regulatory regions, a pattern more typical of other retroviruses.21PLOS Pathogens. The Lentiviral Integrase Binding Protein LEDGF/p75 and HIV-1 Replication
This biology has opened up an entirely different drug-design strategy. If you could disrupt the interaction between integrase and LEDGF/p75, you might block integration through a completely different path from the strand-transfer inhibitors. That idea has led to a class of experimental compounds called allosteric integrase inhibitors, or ALLINIs.
Allosteric Integrase Inhibitors on the Horizon
ALLINIs do not target the catalytic active site the way current INSTIs do. Instead, they bind to a different pocket on the integrase protein, the same pocket that LEDGF/p75 normally occupies. This triggers the integrase molecules to clump together inappropriately, forming large, disordered aggregates. When that happens during viral assembly, new virus particles are produced with their genetic material packaged incorrectly, rendering them unable to infect new cells.22PubMed Central. The structural and mechanistic bases for the viral resistance to allosteric HIV-1 integrase inhibitor pirmitegravir
This is a fundamentally different mechanism from INSTIs. While strand transfer inhibitors block the integration step early in infection, ALLINIs primarily impair the late phase of the viral life cycle, when new virus particles are being assembled and released. In laboratory experiments, virus produced in the presence of ALLINIs is noninfectious.23PubMed Central. Antiviral Activity and Resistance Profile of the Novel HIV-1 Non-Catalytic Site Integrase Inhibitor JTP-0157602 Because ALLINIs hit a different site and work through a different mechanism, they could potentially be used alongside INSTIs, and they might retain activity against viruses that have become resistant to strand transfer inhibitors. Several ALLINIs, including pirmitegravir, are in clinical development, though none has yet reached the market.
Practical Drug Interactions to Know About
INSTIs are generally friendlier than protease inhibitors when it comes to drug interactions, but they are not interaction-free. The most important practical issue involves minerals. INSTIs bind to metal ions as part of their mechanism of action, and that same property means they can bind to metal-containing supplements and medications in the gut. Calcium, iron, magnesium, and aluminum (found in many antacids) can all grab onto the drug before it is absorbed, drastically reducing the amount that reaches the bloodstream. The standard advice is to take INSTIs at least two hours before or six hours after any product containing these minerals, though specific timing varies by drug.
Beyond minerals, dolutegravir has a notable interaction with the tuberculosis drug rifampicin, which speeds up dolutegravir’s metabolism. Since HIV and tuberculosis frequently co-occur, this matters in many parts of the world. The solution is typically to double the dolutegravir dose, but it requires careful management. Bictegravir, by contrast, cannot currently be used alongside rifampicin at all because no dose adjustment has been validated. These interaction profiles can influence which INSTI a clinician chooses for a given patient.
Pediatric Use
Children living with HIV need treatment too, and integrase inhibitors have become important in pediatric care. The challenge is formulation: young children cannot swallow adult-sized tablets, and their drug metabolism differs from adults. Dolutegravir was the first INSTI to be developed as a dispersible tablet and a granule formulation suitable for children, and pharmacokinetic studies confirmed that the granule form delivers adequate drug levels.24PubMed. Relative bioavailability of a paediatric granule formulation of the HIV integrase inhibitor dolutegravir in healthy adult subjects Raltegravir is also available in chewable tablets and granules for younger children. These pediatric formulations have expanded access to the INSTI class in low- and middle-income countries where the burden of pediatric HIV is highest.
The World Health Organization now recommends dolutegravir-based regimens as the preferred first-line treatment for children across all age groups, reflecting both its effectiveness and the availability of weight-band-based dosing formulations. Getting pediatric-friendly versions of the newest drugs to market has historically lagged behind adult approvals by years, and that gap is something the field has been working to close.
Beyond the Active Site
Integrase turns out to do more for HIV than just splice DNA. Research has revealed that the protein also plays a role in viral particle assembly and maturation, functions that have nothing to do with its enzymatic activity. When integrase is absent or defective, the virus produces particles with abnormal core structures that are poorly infectious.25PubMed Central. Going beyond Integration: The Emerging Role of HIV-1 Integrase in Virion Morphogenesis This dual role is part of what makes integrase such an attractive drug target. It also explains why ALLINIs, which cause integrase to aggregate abnormally rather than simply blocking its active site, can produce such profoundly defective virus particles. The more researchers learn about integrase’s non-catalytic functions, the more opportunities emerge for disrupting HIV at multiple stages of its life cycle through a single protein target.