HIV Integrase and Fusion Inhibitor (gp-41) Resistance Testing
What are integrase and fusion inhibitors?
Integrase inhibitors (e.g., raltegravir, aka Isentress) and fusion inhibitors (e.g., enfuvirtide, aka Fuzeon or T-20) are two types of drugs that doctors may prescribe to patients infected with HIV, especially when some of the more common anti-HIV drugs are not working. These are relatively uncommon drugs, although the use of Isentress is increasing in British Columbia as a successful treatment option.
How do integrase and fusion inhibitors work?
The ultimate goal of anti-HIV drug therapy is to reduce the amount of HIV in the patient’s blood (viral load) to an almost ‘undetectable’ level, and reduce the viral reproduction to a minimum.
There are various ways to reduce the virus’s ability to reproduce. HIV must first enter the human cell and then insert its genetic material in order to reproduce. Fusion inhibitors prevent the virus from fusing (attaching) to human cells. Integrase inhibitors prevent HIV from ‘inserting’ its genetic material into human DNA.
What is drug resistance?
Anti-HIV drugs work by stopping the virus from reproducing inside the body. HIV mutates (changes) as it reproduces, and sometimes the mutations make it possible for the virus to grow even in the presence of anti-HIV drugs. When this happens, the virus is said to have drug resistance.
How do we monitor drug resistance?
The BC Centre for Excellence in HIV/AIDS laboratory extracts genetic material from the HIV in the patient’s blood and uses sequencing technology (similar to DNA fingerprinting of the virus) to identify drug resistance mutations. Lists of specific mutations associated with drug resistance against both integrase and fusion inhibitors are available in the scientific literature.
If the patient has had HIV viral load testing at St. Paul’s Hospital, integrase and fusion inhibitor drug resistance testing can be done on stored blood and the patient does not need to have extra blood drawn.
What happens if there is drug resistance?
If resistance to the drug is found, the doctor may consider changing the drug therapy depending on the viral load and remaining treatment options.
Can the likelihood of drug resistance be decreased?
Yes. HIV cannot mutate if it is not reproducing. When anti-HIV drugs are working HIV reproduction is minimal. HIV drugs only work at their best when taken as directed, with no missed pills. This is one key factor in preventing drug resistance.
