atazanavir, Reyataz

  • Pharmacy Author:
    Omudhome Ogbru, PharmD

    Dr. Ogbru received his Doctorate in Pharmacy from the University of the Pacific School of Pharmacy in 1995. He completed a Pharmacy Practice Residency at the University of Arizona/University Medical Center in 1996. He was a Professor of Pharmacy Practice and a Regional Clerkship Coordinator for the University of the Pacific School of Pharmacy from 1996-99.

  • Medical and Pharmacy Editor: Jay W. Marks, MD
    Jay W. Marks, MD

    Jay W. Marks, MD

    Jay W. Marks, MD, is a board-certified internist and gastroenterologist. He graduated from Yale University School of Medicine and trained in internal medicine and gastroenterology at UCLA/Cedars-Sinai Medical Center in Los Angeles.

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 the effect of warfarin (Coumadin). Therefore the effect of warfarin should be monitored more frequently and doses should be modified accordingly.

Combining amiodarone (Cordarone), lidocaine, quinidine, or bepridil (Vascor) with atazanavir may cause dangerous abnormal heart rhythms.

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.

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