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Generic name: cobicistat
Brand name: Tybost
Dosage form: oral tablet (150 mg)
Drug class: Antiviral boosters

Medically reviewed by  A Ras MD.

What is cobicistat?

Cobicistat is a prescription medicine that is used to help the action of some other drugs used to treat HIV (atazanavir or darunavir).


EVOTAZ® is a fixed-dose tablet for oral administration containing the active ingredients atazanavir and cobicistat. Atazanavir is an HIV-1 protease inhibitor. Cobicistat is a mechanism-based inhibitor of cytochrome P450 (CYP) enzymes of the CYP3A family. EVOTAZ tablets contain 342 mg of atazanavir sulfate, equivalent to 300 mg of atazanavir, and 150 mg of cobicistat, as well as the following inactive ingredients in the tablet core: croscarmellose sodium, crospovidone, hydroxypropyl cellulose, magnesium stearate, microcrystalline cellulose, silicon dioxide, sodium starch glycolate, and stearic acid. The tablets are film-coated with a coating material containing the following inactive ingredients: hypromellose, red iron oxide, talc, titanium dioxide, triacetin.

Atazanavir: Atazanavir is present as the sulfate salt. The chemical name for atazanavir sulfate is (3S,8S,9S,12S)-3,12-bis(1,1-dimethylethyl)-8-hydroxy-4,11-dioxo-9-(phenylmethyl)-6-[[4-(2-pyridinyl)phenyl]methyl]-2,5,6,10,13-pentaazatetradecanedioic acid dimethyl ester, sulfate (1:1). Its molecular formula is C38H52N6O7•H2SO4, which corresponds to a molecular weight of 802.9 (sulfuric acid salt). The free base molecular weight is 704.9. Atazanavir sulfate has the following structural formula:


Atazanavir sulfate is a white to pale-yellow crystalline powder. It is slightly soluble in water (4-5 mg/mL, free base equivalent) with the pH of a saturated solution in water being about 1.9 at 24 ± 3°C.

Cobicistat: The chemical name for cobicistat is 1,3-thiazol-5-ylmethyl [(2R,5R)-5-{[(2S)-2-[(methyl{[2-(propan-2-yl)-1,3-thiazol-4-yl]methyl}carbamoyl)amino]-4-(morpholin-4-yl)butanoyl]amino}-1,6-diphenylhexan-2-yl]carbamate. It has a molecular formula of C40H53N7O5S2 and a molecular weight of 776.0. It has the following structural formula:

cobicistat chemical structure

Cobicistat is adsorbed onto silicon dioxide. Cobicistat on silicon dioxide is a white to pale yellow solid with a solubility of 0.1 mg/mL in water at 20°C.

Before taking cobicistat, tell your doctor:

  • If you are allergic to cobicistat; any part of this medicine; or any other drugs, foods, or substances. Tell your doctor about the allergy and what signs you had.
  • If you are taking another drug that has the same drug in it.
  • If you take any drugs (prescription or OTC, natural products, vitamins) that must not be taken with cobicistat, like certain drugs that are used for high cholesterol, HIV, or seizures. There are many drugs that must not be taken with cobicistat.
  • If you have kidney problems and are taking tenofovir.
  • If you have kidney or liver disease and are taking colchicine.
  • If you are pregnant or may be pregnant. Do not take cobicistat if you are pregnant.
  • If you are breast-feeding. Do not breast-feed while you take cobicistat.

This is not a list of all drugs or health problems that interact with cobicistat.

Tell your doctor and pharmacist about all of your drugs (prescription or OTC, natural products, vitamins) and health problems. You must check to make sure that it is safe for you to take cobicistat with all of your drugs and health problems. Do not start, stop, or change the dose of any drug without checking with your doctor.

What are some things I need to know or do while I take cobicistat?

  • Tell all of your health care providers that you take cobicistat. This includes your doctors, nurses, pharmacists, and dentists.
  • This medicine is used with atazanavir or darunavir. Talk with the doctor about the risks and side effects that may happen with those drugs.
  • Have blood work checked as you have been told by the doctor. Talk with the doctor.
  • This medicine interacts with many other drugs. The chance of cobicistat’s side effects may be raised or how well cobicistat works may be lowered. The chance of the other drugs’ side effects may also be raised. This may include very bad, life-threatening, or deadly side effects. Check with your doctor and pharmacist to make sure that it is safe for you to take cobicistat with all of your other drugs (prescription or OTC, natural products, vitamins).
  • This medicine is not a cure for HIV. Stay under the care of your doctor.
  • This medicine does not stop the spread of diseases like HIV or hepatitis that are passed through blood or having sex. Do not have any kind of sex without using a latex or polyurethane condom. Do not share needles or other things like toothbrushes or razors.
  • Do not run out of cobicistat.
  • Very bad kidney problems like kidney failure have happened in people taking cobicistat with tenofovir.
  • Birth control pills and other hormone-based birth control may not work as well to prevent pregnancy. Use some other kind of birth control also like a condom when taking cobicistat.

How is cobicistat best taken?

Use cobicistat as ordered by your doctor. Read all information given to you. Follow all instructions closely.

For all patients taking cobicistat:

  • Take cobicistat with food.
  • Take cobicistat at the same time as the other HIV drug you take it with (atazanavir or darunavir).
  • Keep taking cobicistat as you have been told by your doctor or other health care provider, even if you feel well.
  • It is important that you do not miss or skip a dose of cobicistat during treatment.

When taking cobicistat with atazanavir:

  • Do not take antacids within 2 hours before or 2 hours after taking cobicistat.
  • If you take cimetidine, dexlansoprazole, esomeprazole, famotidine, lansoprazole, nizatidine, omeprazole, pantoprazole, rabeprazole, or ranitidine, ask your doctor or pharmacist how to take it with cobicistat.

What do I do if I miss a dose?

  • Take a missed dose as soon as you think about it.
  • If it is close to the time for your next dose, skip the missed dose and go back to your normal time.
  • Do not take 2 doses at the same time or extra doses.
  • If you are not sure what to do if you miss a dose, call your doctor.

What are the side effects of cobicistat that I need to call my doctor about immediately?

WARNING/CAUTION: Even though it may be rare, some people may have very bad and sometimes deadly side effects when taking a drug. Tell your doctor or get medical help right away if you have any of the following signs or symptoms that may be related to a very bad side effect:

  • Signs of an allergic reaction, like rash; hives; itching; red, swollen, blistered, or peeling skin with or without fever; wheezing; tightness in the chest or throat; trouble breathing, swallowing, or talking; unusual hoarseness; or swelling of the mouth, face, lips, tongue, or throat.
  • Signs of kidney problems like unable to pass urine, change in how much urine is passed, blood in the urine, or a big weight gain.
  • Yellow skin or eyes.

What are some other side effects of cobicistat?

All drugs may cause side effects. However, many people have no side effects or only have minor side effects. Call your doctor or get medical help if you have any side effects that bother you or do not go away.

These are not all of the side effects that may occur. If you have questions about side effects, call your doctor. Call your doctor for medical advice about side effects.

You may report side effects to the FDA at 1-800-332-1088. You may also report side effects at https://www.fda.gov/medwatch.

If overdose is suspected:

If you think there has been an overdose, call your poison control center or get medical care right away. Be ready to tell or show what was taken, how much, and when it happened.

How do I store and/or throw out cobicistat?

  • Store in the original container at room temperature.
  • Keep lid tightly closed.
  • Store in a dry place. Do not store in a bathroom.
  • Keep all drugs in a safe place. Keep all drugs out of the reach of children and pets.
  • Throw away unused or expired drugs. Do not flush down a toilet or pour down a drain unless you are told to do so. Check with your pharmacist if you have questions about the best way to throw out drugs. There may be drug take-back programs in your area.




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