A Potentially Significant Interaction between Efavirenz and Phenytoin: A Case Report and Review of the Literature | Zendy

Sarah Robertson | Zendy; Scott Penzak | Zendy; Jason Lane | Zendy; Alice K. Pau | Zendy; JoAnn M. Mican | Zendy

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A Potentially Significant Interaction between Efavirenz and Phenytoin: A Case Report and Review of the Literature

Author(s) -

Sarah Robertson,

Scott Penzak,

Jason Lane,

Alice K. Pau,

JoAnn M. Mican

Publication year - 2005

Publication title -

clinical infectious diseases

Language(s) - English

Resource type - Journals

SCImago Journal Rank - 3.44

H-Index - 336

eISSN - 1537-6591

pISSN - 1058-4838

DOI - 10.1086/431208

Subject(s) - efavirenz , cyp2b6 , phenytoin , cyp2c19 , pharmacology , medicine , cyp2c9 , cyp3a4 , drug interaction , drug , cytochrome p450 , cyp3a , metabolism , epilepsy , immunology , human immunodeficiency virus (hiv) , psychiatry , viral load , antiretroviral therapy

Although it has not been demonstrated yet, phenytoin is expected to reduce efavirenz exposure through coinduction of cytochrome P450 (CYP) 3A4 and CYP2B6. Conversely, efavirenz has been shown in vitro to inhibit the enzymes responsible for phenytoin metabolism, CYP2C9 and CYP2C19. We report a case in which a potential bidirectional drug interaction between phenytoin and efavirenz resulted in lower-than-expected efavirenz concentrations and elevated phenytoin levels. Therapeutic drug monitoring was used in this case to ensure adequate efavirenz exposure.

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