efavirenz, Sustiva

  • 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 efavirenz?

The recommended dose for adults is 600 mg daily. Efavirenz must be administered in combination with other anti-HIV drugs because the HIV virus quickly becomes resistant to treatment when efavirenz is used alone. Efavirenz should be administered on an empty stomach to improve absorption, preferably at bedtime.

Which drugs or supplements interact with efavirenz?

Efavirenz has many drug interactions because many drugs affect its breakdown and elimination by the liver. Efavirenz also affects the breakdown of other drugs by the liver. The following are some examples of drugs that interact with efavirenz.

Triazolam (Halcion), midazolam (Versed), bepridil (Vascor), pimozide (Orap), and ergot derivatives (for example, ergotamine, dihydroergotamine) should not be combined with efavirenz because efavirenz increases blood levels of these drugs, potentially causing serious adverse effects. St. John's wort should not be combined with efavirenze because it reduces blood levels of efavirenz, leading to possible loss of effectiveness.

Efavirenz increases the breakdown of saquinavir (Invirase) and indinavir (Crixivan). This leads to lower drug concentrations in the body and reduces the effect of saquinavir and indinavir.

Efavirenz increases the concentration of ritonavir (Norvir) while Ritonavir increases the concentration of efavirenz. Increased drug concentrations may result in more frequent or more serious side effects.

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