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- What is atazanavir, and how does it work (mechanism of action)?
- What brand names are available for atazanavir?
- Is atazanavir available as a generic drug?
- Do I need a prescription for atazanavir?
- What are the side effects of atazanavir?
- What is the dosage for atazanavir?
- Which drugs or supplements interact with atazanavir?
- Is atazanavir safe to take if I'm pregnant or breastfeeding?
- What else should I know about atazanavir?
What is atazanavir, and how does it work (mechanism of action)?
Atazanavir is an oral medication that is used for treating infections caused by the human immunodeficiency virus (HIV). It is in a class of drugs called protease inhibitors that also includes ritonavir (Norvir), nelfinavir (Viracept), indinavir (Crixivan) and saquinavir (Invirase, Fortovase). During infection with HIV, the HIV virus multiplies within the body's cells. Viruses are released from the cells and spread throughout the body where they infect other cells. In this manner, HIV infection is perpetuated among new cells that the body produces continually. During the production of the viruses, new proteins must be made. Some of the proteins are structural proteins, that, is, proteins that form the body of the new viruses. Other proteins are enzymes that manufacture DNA and other components for the new viruses. Protease is the enzyme that forms the new structural proteins and enzymes. Atazanavir blocks the activity of protease and results in the formation of new viruses with defective proteins that are unable to infect the body's cells. As a result, the number of viruses in the body (the viral load) decreases. Nevertheless, atazanavir does not prevent the transmission of HIV among individuals, and it does not cure HIV infections or AIDS. Atazanavir was approved by the FDA in June 2003.
What are the side effects of atazanavir?
The most common side effects of atazanavir are:
- muscle pain,
- abdominal pain, and
- jaundice increasing bilirubin in the blood.
Other important side effects include:
- increase in blood glucose levels or an increase or redistribution of body fat;
- Changes in body fat including increased fat in the upper back and neck (buffalo hump), trunk and breasts; and
- a decreased heart rate.
In a small number of patients a serious condition called lactic acidosis--a build up of acid in the blood--may occur. Symptoms of lactic acidosis include persistent nausea, vomiting, weakness and trouble breathing. Individuals with bleeding disorders may bleed more when taking atazanavir.
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What is the dosage for atazanavir?
The starting dose of atazanavir for treatment naive adults is 300 mg atazanavir plus 100 mg ritonavir (Norvir) once daily with food or 400 mg atazanavir once daily with food if unable to tolerate ritonavir.
Ritonavir increases the concentration of atazanavir in the blood. Efavirenz (Sustiva) decreases the concentration of atazanavir in the blood. Therefore, when patients are receiving both atazanavir and efavirenz, 100 mg ritonavir also should be added to 400 mg atazanavir in order to keep the levels of atazanavir in the blood at the desired levels.
Adults who have previously received treatment should not be treated with atazanavir alone. They should receive atazanavir 300 mg plus ritonavir 100 mg once daily or atazanavir 400 mg plus ritonavir 100 mg once daily if also receiving H2-antagonists and tenofovir (Viread) (see drug interactions).
Which drugs or supplements interact with atazanavir?
Atazanavir inhibits the enzymes that eliminate many drugs from the body. Administration of these drugs along with atazanavir may result in increased concentrations of these drugs and cause more side effects. Atazanavir also is eliminated by enzymes in the liver, and drugs that increase the activity of these enzymes may decrease the concentration of atazanavir in the blood and reduce the effect of atazanavir. Conversely, drugs that prevent the elimination of atazanavir may increase the concentration of atazanavir in the blood and cause increased atazanavir-related side effects. Some of the important potential or known interactions are mentioned below. Viewers should consult their health care professional before combining any drugs with atazanavir.
Rifampin (Rifadin), St. John's Wort, tenofovir (Viread), and efavirenz (Sustiva) decrease the blood levels of atazanavir and this can reduce the effect of atazanavir. Dose modifications are necessary when atazanavir is combined with efavirenz or tenofovir. Rifampin and St. John's Wort should not be combined with atazanavir.
Atazanavir decreases the elimination and, therefore, could increase the side effects of triazolam (Halcion), midazolam (Versed), bepridil (Vascor), verapamil (Isoptin) , diltiazem (Cardizem), lovastatin (Mevacor), simvastatin (Zocor), atorvastatin (Lipitor), pimozide (Orap), irinotecan (Camptosar), cyclosporine (Sandimmune), rifabutin (Mycobutin), amiodarone (Cordarone), clarithromycin (Biaxin), alfuzosin (Uroxatral), and ergot drugs (Migranal, Cafergot). Combining atazanavir with lovastatin, simvastatin, pimozide, triazolam, midazolam, irinotecan, ergot drugs, or alfuzosin is contraindicated.
Atazanavir is best absorbed under acidic conditions. Therefore, medications that decrease stomach acidity could reduce the absorption of atazanavir. Drugs that decrease stomach acidity include antacids, proton pump inhibitors such as omeprazole (Prilosec), lansoprazole (Prevacid), pantoprazole (Protonix), rabeprazole (Aciphex) esomeprazole (Nexium); H2-receptor antagonists such as cimetidine (Tagamet), ranitidine (Zantac), famotidine (Pepcid), nizatidine (Axid); and buffered drugs such as didanosine (Videx). Individuals who are taking antacids or didanosine should take their atazanavir two hours before or one hour after the didanosine or antacid. Proton pump inhibitors should not be combined with atazanavir in previously treated patients. For treatment naive patients the dose of proton pump inhibitor should not exceed the equivalent of omeprazole 20 mg and must be given 12 hours before administration of atazanavir. The dose of H2-antagonists should not exceed the equivalent of 40 mg famotidine twice daily and atazanavir should be administered 2 hours before or 10 hours after administration of the H2-antagonists.
Atazanavir increases blood levels of PDE5 inhibitors such as sildenafil (Viagra, Revatio), tadalafil (Adcirca, Cialis), and vardenafil (Levitra). Atazanavir should not be combined with Revatio (sildenafil used for treating pulmonary hypertension). It should be used with caution with reduced doses of the other PDE5 inhibitors.
Is atazanavir safe to take if I'm pregnant or breastfeeding?
Atazanavir has not been adequately studied in pregnant women.
Atazanavir has not been adequately studied in nursing mothers. Scientific experts advise HIV-infected mothers not to breastfeed because of the risk of transmitting HIV to the infant.
What else should I know about atazanavir?
What preparations of atazanavir are available?
Capsules: 100, 150, 200, and 300 mg
How should I keep atazanavir stored?
Atazanavir should be stored at room temperature, between 15 C to 30 C (59 F to 86 F).
Reference: FDA Prescribing Information
Atazanavir (Reyataz) is a drug prescribed for the treatment of HIV infections. Side effects, drug interactions, and patient warnings should be reviewed prior to taking this medication.
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