Cytochrome P450 and antifungal agents

Ref ID: 5214

Author:

R. Stahlmann

Author address:

Institute for Clinical Pharmacology and Toxicology, Charité Universitätsmedizin Berlin, Campus Benjamin Franklin,
Berlin, Germany

Full conference title:

2nd Trends in Medical Mycology

Abstract:

Systemically acting antifungal agents can cause pharmacokinetic or pharmacodynamic drugdrug interactions by a variety of
mechanisms.
The systemic azoles, such as ketoconazole, itraconazole, fluconazole and voriconazole, differ with respect to their lipophilicity and
metabolism, but all of them are inhibitors of cytochrome P450 (CYP) isoenzymes.
They exert their fungistatic effect by inhibiting the specific fungal CYP51A1-dependent C-14 a-demethylase (lanosterol demethylase),
the enzyme necessary for the conversion of lanosterol to ergosterol. Despite significant differences in their affinity to fungal and human
cytochromes, the systemic azoles are also substrates and inhibitors of human CYP isoforms, such as CYP3A4, CYP2C9 and CYP2C19,
to varying degrees. In addition, some are substrates of the MDR-1 gene product, Pglycoprotein (P-gp). These features are the basis for
most of the interactions occurring during azole therapy, e.g. in severely ill patients in the hospital who are treated with multiple drugs. It
must be considered that a dose adjustment of concomittantly given drugs is not only necessary when an azole is added to themedication
list of a patient, but also when therapy with the azole is stopped. In addition it seems noteworthy to mention that antifungal substances
like fluconazole and itraconazol are used increasingly often for the treatment of genital mycoses and mycoses of the skin in outpatients.
This has increased the likelihood for drug interactions also in an ambulatory setting. For evaluation of the clinical importance of drug
interactions, a specific combination of drugs can either be (a) absolutely contraindicated, (b) acceptable when accompanied by drug level
monitoring or dose adjustment or (c) have a sufficiently low drug interaction potential allowing concomitant administration without
precautions.

Abstract Number: S01.4

Slides: y

Conference Year: 2005

Link to conference website: NULL

New link: NULL

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