HIV/AIDS Treatment How HIV Booster Drugs Work By James Myhre & Dennis Sifris, MD Dennis Sifris, MD, is an HIV specialist and Medical Director of LifeSense Disease Management. James Myhre is an American journalist and HIV educator. Learn about our editorial process James Myhre & Dennis Sifris, MD Fact checked by Fact checked by Ashley Hall on July 27, 2020 linkedin Ashley Hall is a writer and fact checker who has been published in multiple medical journals in the field of surgery. Learn about our editorial process Ashley Hall on July 27, 2020 Print There are drugs used in the treatment of HIV that can increase the plasma concentration of certain antiretroviral agents (ARVs) when used in combination therapy. Popularly known as "boosters," the drugs allow doctors to reduce the dosage and frequency of the attendant ARV while lowering the potential for drug-related side effects. HIV boosters, also known as pharmacokinetic enhancers, should not be confused with vitamins or supplements marketed as "immune boosters," which have no known properties for either preventing or fighting HIV infection. Joe Raedle / Getty Images The Introduction of HIV Boosters When HIV protease inhibitors (PIs) were first discovered in the mid-1990s, one of the main challenges to researchers was the rapid speed in which the drugs were metabolized in the liver and cleared from the bloodstream. As a result, PIs required twice- to thrice-daily dosing. Not only did the high dosages increase the risk of drug toxicities, the high pill burden made adherence all the more difficult (and the development of resistance all the more likely). In 1996, the drug Norvir (ritonavir) was approved for use in HIV by the U.S. Food and Drug Administration (FDA). While the drug was known to have antiviral properties, it was soon discovered that, even at very low doses, it could inhibit the very enzyme (CYP3A4) needed to metabolize PIs. The discovery immediately impacted the way in which PIs were prescribed. Today, Norvir is rarely used for its antiviral action, but rather to increase the efficacy of the attendant PIs, while reducing the adverse effects associated with therapy. The drug is also a component of the fixed-dose combination PI, Kaletra (lopinavir + ritonavir). (Please note: Norvir can interfere with plasma concentrations of other drugs you may be taking, sometimes resulting in serious to severe interactions. Please advise your doctor about any concomitant medications you are using when either Norvir or Kaletra is prescribed.) The Future of HIV Boosters In recent years, there has been much focus placed on the development of other HIV boosters. It is envisioned that similar agents might not only further extend the efficacy of PIs, but do the same for other classes of ARVs—potentially affording unified, once-daily doses, while allowing greater "forgiveness" should a dose be missed or a gap in therapy occurs. In 2012, a full 16 years after the introduction of Norvir, a second booster drug was finally approved by the FDA. Tybost (cobicistat), a component of the fixed-dose combination drug Stribild (elvitegravir + cobicistat + tenofovir + emtricitabine), is shown to inhibit both the CYP3A4 enzyme and certain intestinal proteins known to interfere with drug absorption. While it has no antiviral properties of its own, Tybost is able to increase the efficacy of elvitegravir, an HIV integrase inhibitor, while achieving similar results with the PIs Reyataz (atazanavir) and Prezista (darunavir) and the nucleotide analog Viread (tenofovir). In early 2015, the FDA approved two, fixed-dose combination drugs incorporating Tybost, including Evotaz (atazanavir + cobicistat) and Prezcobix (darunavir + cobicistat). Other experimental boosters are under investigation, including a novel CYP3A4 inhibitor being developed by Sequoia Pharmaceuticals. Was this page helpful? Thanks for your feedback! Get information on prevention, symptoms, and treatment to better ensure a long and healthy life. Sign Up You're in! Thank you, {{form.email}}, for signing up. There was an error. Please try again. What are your concerns? Other Inaccurate Hard to Understand Submit Article Sources Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy. Gallant JE, Koenig E, Andrade-Villanueva J, et al. Cobicistat versus ritonavir as a pharmacoenhancer of atazanavir plus emtricitabine/tenofovir disoproxil fumarate in treatment-naive HIV type 1-infected patients: week 48 results. J Infect Dis. 2013;208(1):32-39. doi:10.1093/infdis/jit122 U.S. Department of Health & Human Services. AIDS Info. FDA approves new combination pill for HIV treatment for some patients. Published August 27, 2012.