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Efavirenz

Efavirenz (brand names Sustiva® and Stocrin®) is non-nucleoside reverse transcriptase inhibitor (NNRTI) and is used as part of high active antiretroviral therapy (HAART) for the treatment of a human immunodeficiency virus (HIV) type 1. more...

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For HIV infection that has not previously been treated, efavirenz and lamivudine in combination with zidovudine, tenofovir or stavudine is the preferred NNRTI-based regimen.

Efavirenz is also used in combination with other antiretroviral agents as part of an expanded postexposure prophylaxis regimen to prevent HIV transmission for those exposed to materials associated with a high risk for HIV tranmission. The usual adult dose is 600 mgs once a day taken on an empty stomach at bedtime.

History

Efavirenz was approved by the Food and Drug Administration (FDA) on Sep 21, 1998, making it the fourteenth approved antiretroviral drug.

Drug interactions

Efavirenz is metabolized in the liver, and possesses both inhibitory and inducing effects on the 3A4 isoform of the cytochrome P450 system. This means efavirenz may interact with other drugs metabolized in the liver, requiring either increased or decreased dosages.
Efavirenz lowers blood levels of most protease inhibitors. Dosages of amprenavir, atazanavir, or indinavir may need to be increased. The blood levels of saquinavir are dramatically lowered, so that the two drugs cannot be used simultaneously.
St. John's Wort and garlic supplements may decrease efavirenz blood levels.

Side effects

Psychiatric symptoms, including insomnia, confusion, memory loss, and depression, are common.
rash nausea dizziness and headache may occur
efavirenz can cause birth defects
safety in children has not been established
use of efavirenz can cause a false positive in some urine tests for marijuana

Mechanism of action

Efavirenz is chemically described as (S)-6-chloro-(cyclopropylethynyl)-1,4-dihydro-4-(trifluoromethyl)-2H-3,1-benzoxazin-2-one. Its empirical formula is C₁₄H₉ClF₃NO₂. Efavirenz is a white to slightly pink crystalline powder with a molecular mass of 315.68. It is practically insoluble in water (<10 µg/mL).

Read more at Wikipedia.org

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Failure of tenofovir + abacavir + 3TC combination; full report published, more insight
From AIDS Treatment News, 10/1/05 by John S. James

In 2003 researchers stopped a clinical trial abruptly when they found that a combination of three drugs that seemed likely to work well together failed to control the virus in many patients, and led to a very high rate of viral resistance; a comparison regimen that used efavirenz instead of the tenofovir worked well. A similar combination (tenofovir plus abacavir plus ddI) also failed. However, regimens that include AZT do not fail in this way. The problem was completely unexpected, and since it occurred, several different theories were proposed.

No one knows the answer for sure--and we will probably never know, since it would be unethical to test the failed triple combinations in patients with HIV. But many researchers now believe the most likely explanation is that the drug combinations failed to control the virus because of a low genetic barrier to HIV resistance. Two mutations that developed in this trial protect the virus against the three drugs.

The December 1, 2005 Journal of Infectious Diseases published the full report of the trial [1] and a commentary [2]; both are available free online.

"The most likely explanation is the low genetic barrier to resistance produced by synergistic selection pressure from all 3 drugs for 2 point mutation, M184V and K65R. Both abacavir and tenofovir DF select for the K65R mutation, which reduces susceptibility to both drugs, as well as to lamivudine [3TC]. M184V is selected for by lamivudine and abacavir, and it decreases susceptibility to both. Thus, the selection of 2 mutations, each of which may preexist as minority species, leads to virologic failure with this regimen." [1]

The authors conclude that physicians should not try new combinations on their own as the first antiretroviral treatment for patients. "Given the growing number of potent, well-studied combinations now available, there is no longer a rationale for the use of untested regimens outside of clinical trials in the treatment of therapy-naive HIV-infected patients." [1]

References

Note: Both articles below were made available free online by the journal; you do not need to be a subscriber.

They are available through the Table of Contents of the December 1 issue, http://www.journals.uchicago.edulJID/journal/contents/v192n11.html

(1.) Gallant JE, Rodriguez AE, Weinberg WG, and others. for the ESS30009 study. Early virologic nonresponse to tenofovir, abacavir, and lamivudine in HIV-infected antiretroviral-naive subjects. Journal of Infectious Diseases. December 1,2005; volume 192, pages 1921-1930.

(2.) Kuritzkes DR. Less than the sum of its parts: Failure of a tenofovir-abacavir-lamivudine triple-nucleoside regimen. Editorial commentary. Journal of Infectious Diseases. December 1,2005; volume 192, pages 1867-1868.

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