Tretinoin Ketoconazole

Fluconazole inhibits the cytochrome P450 isoenzymes CYP3A4 and CYP2C9, which are amongst those involved in the oxidative metabolism of tretinoin, and it was suggested that this resulted in increased plasma levels of tretinoin. Another study has also shown that fluconazole may inhibit the ADPH-dependent cytochrome P450-mediated metabolism of tretinoin. Ketoconazole may similarly affect the pharmacokinetics of tretinoin. ... 

A potential interaction of ketoconazole with tretinoin (all-trans retinoic acid), resulting in slowed metabohsm, is probably not of importance (56). 

The metabolism of tretinoin can be inhibited by fluconazole, and a case report describes tretinoin toxicity as a result of this interaction. Ketoconazole may interact similarly. 

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