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Eur J Clin Pharmacol. 2007 May;63(5):479-83. Epub 2007 Mar 8.

Effect of efavirenz on the pharmacokinetics of ketoconazole in HIV-infected patients.

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  • 1Department of Medicine, Faculty of Medicine, Prince of Songkla University, Hat Yai, Songkhla 90110, Thailand.



To investigate the effect of efavirenz on the ketoconazole pharmacokinetics in HIV-infected patients.


Twelve HIV-infected patients were assigned into a one-sequence, two-period pharmacokinetic interaction study. In phase one, the patients received 400 mg of ketoconazole as a single oral dose on day 1; in phase two, they received 600 mg of efavirenz once daily in combination with 150 mg of lamivudine and 30 or 40 mg of stavudine twice daily on days 2 to 16. On day 16, 400 mg of ketoconazole was added to the regimen as a single oral dose. Ketoconazole pharmacokinetics were studied on days 1 and 16.


Pretreatment with efavirenz significantly increased the clearance of ketoconazole by 201%. C(max) and AUC(0-24) were significantly decreased by 44 and 72%, respectively. The T ((1/2)) was significantly shorter by 58%.


Efavirenz has a strong inducing effect on the metabolism of ketoconazole.

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