Tybost reduces the action of enzymes in your liver that break down certain antiviral medicines. This allows the antiviral medicines to be used more safely and effectively at lower doses.

Tybost is given together with atazanavir (Reyataz) or darunavir (Prezista) to treat human immunodeficiency virus (HIV), the virus that can cause acquired immunodeficiency syndrome (AIDS).

Tybost is used to increase your blood levels of these medicines, helping to make them safer and more effective at lower doses.

When given with atazanavir, Tybost is for use in adults and children weighing at least 77 pounds (35 kilograms). When given with darunavir, Tybost is for use in adults and children weighing at least 88 pounds (40 kilograms).

Tybost is not an antiviral medicine and will not treat HIV or AIDS. It is given only to help increase your blood levels of atazanavir or darunavir.

Tybost is not a complete treatment and must be used in combination with other antiviral medicines your doctor has prescribed. However, there are certain antiviral medicines that should not be taken in combination with cobicistat. Follow your doctor's medication and dosing instructions very carefully.

Tybost is recommended for use only with atazanavir or darunavir. You should not take this medicine with other protease inhibitor HIV medicines, such as fosamprenavir, nelfinavir, saquinavir, or tipranavir.

You should not take cobicistat with darunavir if you are taking darunavir twice daily. You should not take cobicistat with atazanavir if you also take indinavir, irinotecan, or nevirapine.

Many drugs can interact with cobicistat and some should not be used at the same time. Tell your doctor about all your current medicines and any you start or stop using.

Tybost is usually taken once per day with atazanavir or darunavir.

Follow all directions on your prescription label and read all medication guides or instruction sheets. Use the medicine exactly as directed.

Take your HIV medicines with food at the same time each day to be sure you do not miss a dose.

If you take Tybost with atazanavir and you also take medicine to reduce stomach acid, follow these recommendations unless your doctor tells you otherwise:

• If you take an antacid, take it at least 2 hours before or 2 hours after you take Tybost and atazanavir.

• If you take a medicine such as cimetidine, ranitidine, Tagamet, Axid, Zantac, Pepcid, and others: Take the stomach medicine at the same time you take Tybost and atazanavir; or wait at least 10 hours after taking the stomach medicine to take your Tybost and atazanavir doses.

• If you take a proton pump inhibitor such as omeprazole, esomeprazole, Nexium, Prevacid, Prilosec, Protonix: Wait at least 12 hours after taking the stomach medicine to take your Tybost and atazanavir doses.

While using Tybost, your blood may need to be tested often. Your kidney function may also need to be tested.

Use all HIV medications as directed and read all medication guides you receive. Do not change your dose or dosing schedule without your doctor's advice. Every person with HIV should remain under the care of a doctor.

Store in the original container at room temperature, away from moisture and heat. Keep the bottle tightly closed when not in use.

Usual Adult Dose for HIV Infection:

150 mg orally once a day with food

Comments:
-This drug must be used with atazanavir or darunavir; the manufacturer product information for these agents should be consulted.
-This drug may be used with atazanavir (300 mg orally once a day) in therapy-naive and therapy-experienced patients.
-This drug may be used with darunavir (800 mg orally once a day) in therapy-naive patients and therapy-experienced patients with no darunavir resistance associated substitutions.
-This drug is not interchangeable with ritonavir and should not be used with darunavir 600 mg twice a day, fosamprenavir, saquinavir, or tipranavir.

Use: To increase systemic exposure of atazanavir or darunavir in combination with other antiretrovirals in the treatment of HIV-1 infection

Tybost is not a complete treatment and must be used in combination only with atazanavir or darunavir. You should not take this medicine with any other antiviral medicines that your doctor has not prescribed.

You should not take Tybost if you are allergic to cobicistat.

Many drugs can interact and cause dangerous effects that could lead to death. Some drugs should not be used together.

You should not take cobicistat with atazanavir if you also take:

• indinavir;

• irinotecan;

• nevirapine; or

• birth control pills that contain drospirenone and ethinyl estradiol (Beyaz, Sayfral, Yasmin, Yaz).

You should not take Tybost with atazanavir or darunavir if you also take:

• alfuzosin;

• cisapride;

• colchicine;

• dronedarone;

• oral midazolam, or triazolam;

• ranolazine;

• rifampin;

• sildenafil (Revatio, for treating pulmonary arterial hypertension);

• St. John's wort;

• antipsychotic medicine - lurasidone, pimozide;

• cholesterol medication - lomitapide, lovastatin, simvastatin;

• ergot medicine - dihydroergotamine, ergotamine, methylergonovine; or

• seizure medication - carbamazepine, phenobarbital, phenytoin.

You may not be able to take Tybost if you also take:

• darunavir 600 milligrams twice daily; or

• certain other antiviral medicines - fosamprenavir, saquinavir, or tipranavir.

To make sure this medicine is safe for you, tell your doctor if you have ever had:

• liver disease; or

• kidney disease, especially if you also take tenofovir.

Tybost may not work as well if you take it during pregnancy. Do not start taking the medicine if you are pregnant. Tell your doctor right away if you become pregnant.

If you plan to get pregnant, ask your doctor for another antiviral medicine to use during pregnancy. Use all medications properly to control your infection. HIV can be passed to your baby if the virus is not controlled during pregnancy. Your name may be listed on a registry to track any effects of antiviral medicine on the baby.

If you do not plan to get pregnant, ask your doctor about using a non-hormonal birth control (condom, diaphragm with spermicide) to prevent pregnancy. Cobicistat can increase certain side effects when taken with hormonal birth control (pills, injections, implants, skin patches, vaginal rings).

Women with HIV or AIDS should not breastfeed a baby. Even if your baby is born without HIV, the virus may be passed to the baby in your breast milk.

Take the medicine as soon as you can, but skip the missed dose if it is almost time for your next dose. Do not take two doses at one time.

Get your prescription refilled before you run out of medicine completely.

Seek emergency medical attention or call the Poison Help line at 1-800-222-1222.

Using this medicine will not prevent your disease from spreading. Do not have unprotected sex or share razors or toothbrushes. Talk with your doctor about safe ways to prevent HIV transmission during sex. Sharing drug or medicine needles is never safe, even for a healthy person.

Get emergency medical help if you have signs of an allergic reaction to Tybost: hives; difficult breathing; swelling of your face, lips, tongue, or throat.

Call your doctor at once if you have:

• kidney problems - little or no urination, swelling in your feet or ankles, feeling tired or short of breath; or

• liver problems - upper stomach pain, loss of appetite, dark urine, clay-colored stools, jaundice (yellowing of the skin or eyes).

Common Tybost side effects may include:

• nausea;

• jaundice; or

• rash.

This is not a complete list of side effects and others may occur. Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.

When you start or stop taking Tybost, your doctor may need to adjust the doses of any other medicines you take on a regular basis.

Sometimes it is not safe to use certain medications at the same time. Some drugs can affect your blood levels of other drugs you take, which may increase side effects or make the medications less effective.

Tell your doctor about all your current antiviral medicines.

Many drugs can interact with cobicistat, and some drugs should not be used at the same time. Tell your doctor about all your current medicines and any medicine you start or stop using. This includes prescription and over-the-counter medicines, vitamins, and herbal products. Not all possible interactions are listed here.