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Isentress (raltegravir)

Pronunciation(s): eye-SEN-tress, ral-TEG-ra-veer

What is Isentress?
  • Isentress is an integrase inhibitor manufactured by Merck & Company. It was approved by the U.S. Food and Drug Administration (FDA) in October 2007. Isentress is approved both for treatment-experienced patients who have HIV strains that are resistant to multiple antiretroviral (ARV) drugs and for people with drug-sensitive HIV strains, such as those starting antiretroviral therapy for the first time.
  • After HIV's genetic material is deposited inside a cell, its RNA must be converted (reverse transcribed) into DNA. A viral enzyme called integrase then helps to hide HIV's DNA inside the cell's DNA. Once this happens, the cell can begin producing genetic material for new viruses. Integrase inhibitors, such as Isentress, are designed to block the activity of the integrase enzyme and to prevent HIV DNA from meshing with healthy cell DNA.
  • Isentress must be used in combination with other HIV drugs.
  • Merck has established a patient assistance program (PAP) for people living with HIV who do not have private or public health insurance and are unable to afford Isentress. To learn more about the PAP for Isentress, call 800-850-3430. For those with private health insurance, a program has been established to help cover each Isentress co-payment, up to $400 every month. To learn more about this co-pay program, click here.
What is already known about Isentress?
  • The Isentress dose is one 400mg tablet taken by mouth twice a day. It can be taken with or without food.
  • Isentress holds promise for HIV-positive patients who no longer respond to other HIV drugs. Because Isentress targets HIV differently than all other available antiretrovirals, chances are that many people living with the virus—regardless of which drugs have failed them in the past—will likely benefit from using Isentress. Two large large Phase III clinical trials have determined that Isentress, when combined with other drugs, is effective for patients whose virus has adapted to other HIV drugs used in the past. However, Isentress worked best when it was combined with at least two other drugs that the virus was sensitive to. For this reason, it is best to use drug-resistance testing to determine which drugs your virus is sensitive to; the results will show which antiretrovirals are best to combine with Isentress.
  • Isentress is also approved for people who have not yet taken ARV therapy. Isentress, combined with Truvada (tenofovir and emtricitabine), is listed as a "preferred" option for first-time treatment takers by the United States Department of Health and Human Services in its official HIV treatment guidelines. To learn more about these recommendations and options, click here.
  • Isentress was approved in December 2011 for children two years of age and older. Chewable tablets, in 100mg and 25mg strengths, have also been approved for children. Pediatric Isentress dosing is based on the age and weight of the child. If the chewable tablets are used, the dose should not exceed 300mg ever 12 hours. It is important to note that the Isentress chewable tablets contain phenylalanine, a component of the sugar substitute aspartame. Phenylalanine can be harmful to children and adults with phenylketonuria, a birth defect that can lead to a variety of health problems and requires a diet that limits the intake of phenylalanine. To learn more about treatment options for children, click here.
What about drug interactions?
  • Isentress is broken down (metabolized) by the body differently than most medications used to treat HIV and AIDS. This means that Isentress likely has fewer drug interactions when combined with protease inhibitors, non-nucleoside reverse transcriptase inhibitors, methadone, opioid pain relievers, statins, antifungals, proton pump inhibitors, oral contraceptives, and erectile dysfunction drugs.
  • At the time of Isentress' approval in October 2007, there were no known "contraindications," meaning that there are no known medications that must be avoided while taking Isentress.
  • Isentress can interact with Rifadin (rifampin), a medication used to treat TB, MAC, and other bacterial infections. Rifadin (rifampin) can decrease Isentress levels in the bloodstream. While Isentress dosing adjustments haven't been recommended, caution is recommended if both drugs are used together.
  • Isentress can interact with a few HIV medications. Aptivus (tipranavir), combined with Norvir (ritonavir), can decrease levels of Isentress in the bloodstream. However, in a clinical trial involving patients who took both drugs, treatment efficacy was not compromised. Reyataz (atazanavir), combined with Norvir, can increase Isentress levels in the bloodstream. In clinical trials, this was not associated with an increased risk of Isentress side effects. Based on these findings, Isentress dose adjustments are not recommended if it is combined with either Aptivus/Norvir or Reyataz/Norvir.
  • Isentress might interact with drugs that are called "UGT inducers." These include, among other drugs, some anticonvulsants and some atypical antipsychotics.
  • Interactions between Isentress and other medications may be discovered. Tell your doctors and pharmacists about all medicines you take. This includes those you buy over-the-counter and herbal or natural remedies. Bring all your medicines when you see a doctor, or make a list of their names, how much you take, and how often you take them. Your doctor can then tell you if you need to change the dosages of any of your medications.
What is known about side effects?
  • The side effects most commonly reported among study volunteers who received Isentress were diarrhea, nausea, and headache.
  • Blood tests showed abnormally elevated levels of a muscle enzyme—creatine kinase—in some patients receiving Isentress. According to the FDA, Isentress should be used with caution by patients who are at an increased risk of muscle problems like myopathy and rhabdomyolysis, which includes patients using other medications known to cause these conditions.
Can pregnant women take Isentress?
  • Isentress is classified by the FDA as a pregnancy category C drug. Pregnancy category C means that animal studies have shown an adverse effect on the fetus and there are no adequate and well-controlled studies in humans, but potential benefits may warrant use of the drug in pregnant women despite potential risks. HIV-positive women who become pregnant should discuss the benefits and possible side effects of HIV treatment to help protect their babies from HIV (see our lesson called Family Planning, Pregnancy & HIV).
  • It is not known whether Isentress passes into breast milk and what effect it may have on a nursing baby. To prevent transmission of the virus to uninfected babies, it is recommended that HIV-positive mothers not breast-feed.
Where can I learn more about clinical trials of Isentress?
  • If you would like to find out if you are eligible for any clinical trials that include Isentress, visit, a site run by the U.S. National Institutes of Health. The site has information about all HIV-related clinical studies in the United States. For more info, you can call their toll-free number at 1-800-HIV-0440 (1-800-448-0440) or email

Last Revised: December 22, 2011

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