AEGiS-GMHC: Treatment Briefs: Efavirenz's Complications

Important note: Information in this article was accurate in 1998. The state of the art may have changed since the publication date.

Treatment Briefs: Efavirenz's Complications

Treatment Issues, Volume 12, Number 5 - May 1998
Dave Gilden

DuPont Merck, which is soon to become simply DuPont Pharmaceuticals as the result of a recent buyout by DuPont, sent out a warning on May 21 concerning use of its new NNRTI (nonnucleoside reverse transcriptase inhibitor) efavirenz (Sustiva) along with the protease inhibitor saquinavir (Fortovase). Preliminary findings in an HIV-negative cohort indicate that efavirenz cuts saquinavir blood levels by 60% over the course of a day. This reduction stems from efavirenz's stimulation of the CYP3A4 liver enzyme that degrades saquinavir. The company is urging patients not to take the two drugs together until further information on correct dosing is available. An exception to this warning concerns use of the dual protease inhibitor combination saquinavir/ritonavir (Norvir). This combination is the most common saquinavir regimen. It is taken by 22% of the persons in the efavirenz expanded access program. Ritonavir strongly inhibits liver enzymes and may reverse efavirenz's effect on saquinavir, but no data are yet available to determine the result of taking the three drugs together. One possibility that some doctors are trying is to double the saquinavir dose to 800 mg twice a day when efavirenz is administered with ritonavir/saquinavir.

The company intends to present information on the interaction between efavirenz, ritonavir and saquinavir this June-July at the World AIDS Conference in Geneva. Data on the interaction between nelfinavir (Viracept) and efavirenz also will be made public at the Conference, as will the results of a large study comparing the "protease sparing" regimen of AZT/3TC/efavirenz to both indinavir/efavirenz and AZT/3TC/ indinavir. Note that DuPont Merck has long recommended increasing the indinavir dose by 25% (to 1,000 mg three times a day) when administering the protease inhibitor indinavir along with efavirenz.

DuPont Merck also expects to file by mid-June for FDA approval of efavirenz for treating HIV infection, whether as first-line or salvage therapy, as part of a multidrug regimen.

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