Integrase Inhibitors (INIs) – drugs that block the action of the integrase enzyme -  represent a relatively new area in HIV/AIDS treatment.

In HIV replication, integrase allows the virus to insert, or “integrate,” its genetic material into the host cell’s DNA. As a result, the infected CD4, or “T-helper,” cell produces copies of the virus instead of new proteins for the cell’s own use.

This stage of HIV infection allows the host cell to create more copies of the virus to spread and infect other healthy cells.

Though researchers do not entirely understand how the enzyme acts, managing integrase through drug therapy has promising results thus far. The therapy is known to suppress and reduce a patient’s “viral load,” or the number of HIV copies in one milliliter of blood, because infected cells do not replicate more copies of the virus.

INIs are usually used in combination with other antiretroviral drugs – which target viruses like HIV that make copies of themselves in host cells. Unlike the majority of antiretroviral drugs, INIs are seen as a last resort to patients who have developed resistance to drugs.

Most INIs are taken orally in the form of pills, and long-term side effects of the drugs are still being studied. Specialists rarely prescribe INIs for patients who have not started antiretroviral treatments or patients who are responsive to other drugs.

The first FDA-approved INI was Isentress (raltegravir) in 2007. Some of the reported side effects of the drug were diarrhea, nausea, headache, and fever. In more severe cases, patients reported rash, Stevens-Johnson syndrome (a heightened mucous and skin reaction to a medication or infection), and depression.

Some INIs were discontinued during Phase 2 trials because of their toxicity – or degree to which a substance can harm an organism – in dogs. Elvitegravir, also known as “GS-9137,” is currently in Phase 3 trial by Gilead Sciences, Inc.