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AIDS virusTybost belongs to a class of anti-HIV drugs called Pharmacokinetic Enhancers. For a description of the life-cycle of the AIDS virus, and the targets of each class of drugs, click here.

Tybost is being developed by Gilead Sciences. They have a web site that includes the latest news & research reports on this and other drugs in development: click here.

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Tybost (cobicistat)


What is Tybost?
  • Tybost (cobicistat) is a pharmacokinetic enhancer (a drug used to boost other medications in the blood to make them more effective) by Gilead Sciences. It is a stand-alone drug, for use in combination with either Reyataz (atazanavir) and Prezista (darunavir), and as a component of the fixed-dose combination tablet Stribild.
  • Tybost is not active against HIV. It works by inhibiting an enzyme called CYP3A4 that is responsible for breaking down (or metabolism) of certain medications, including several HIV drugs. This helps boost the effectiveness of these drugs, while allowing fewer pills or doses on a daily basis.
  • cobicistat was developed to be used in combination with other drugs.

What is already known about Tybost?
  • The Tybost dose is 150 mg, once a day, in combination with either Reyataz or Prezista. Stribid contains 150 mg cobicistat.
  • Compared with Norvir (ritonavir), an HIV protease inhibitor frequently used to boost other antiretrovirals, Tybost blocks fewer ezymes in the body responsible for breaking down (metabolizing) drugs, meaning that it will likely result in fewer drug-drug interactions. However, Tybost still interacts with a number of medications, including those used to treat HIV. It is important that your health care provider be aware of all drugs you are taking, including those you buy without a prescription.
  • Stribild contains cobicistat, the integrase inhibitor elvitegravir, tenofovir (found in Viread, Truvada, Complera and Atripla) and emtricitabine (found in Emtriva, Truvada, Complera and Atripla). Cobicistat is also being studied in fixed-dose combination tablets containing Reyataz and Prezista.

What about drug interactions?
  • Like the protease inhibitor Norvir (ritonavir), which is primarily used to boost blood levels of other HIV medications in the body, Tybost has a number of interactions with other (HIV and non-HIV) drugs. However, Tybost only affects the CYP3A4 enzyme, whereas Norvir interacts with CYP3A4 and others. Studies on potential interactions between cobicistat and other drugs are ongoing.

What is known about side effects?
  • According to clinical trials completed thus far, Tybost may cause gastrointestinal side effects, including nausea, vomiting and diarrhea. The drug may also exacerbate kidney impairment in some people.

Who should not take Tybost?
  • It is not known whether Tybost will harm an unborn baby. It is very important to treat HIV/AIDS during pregnancy to reduce the risk of infecting your baby. Talk to your doctor about your treatment options.
  • It is not known whether Tybost 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 Tybost?
  • If you would like to find out if you are eligible for any clinical trials that include Tybost, visit ClinicalTrials.gov, 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 contactus@aidsinfo.nih.gov.

Last Revised: August 28, 2012

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