<prompt> For systemic mycosis fluconazole is preferred over ketoconazole because of -Greater efficacyLonger t12Lesser side effectsAll the above  <response>: Ans. is d i.e., All the above Imidazoles and Triazoles These are presently the most extensively used antifungal drugs. Four imidazoles are entirely topical, while ketoconazole is used both orally and topically. Two triazoles fluconazole and itraconazole have largely replaced ketoconazole for systemic mycosis because of greater efficacy, Longer 112, fewer side effects and drug interactions. The imidazoles and triazoles have broad spectrum antifungal activity covering dermatophytes, Candida, other fungi involved in deep mycosis except mucor, Nocardia, some gram positive and anaerobic bacteria, e.g. Staph, aureus, Strep, faecalis, Bac. fragilis and Leishmania. The mechanism of action of imidazoles and triazoles is the same. They inhibit the fungal cytochrome P450 enzyme Tanosterol 14-demethylase and thus impair ergosterol synthesis leading to a cascade of membrane abnormalities in the fungus. The lower host toxicity of triazoles compared to imidazoles has correlated with their lower affinity for mammalian CYP450 enzymes and lesser propensity to inhibit mammalian sterol synthesis. However, because they are active against certain bacteria as well which do not have ergosterol, other mechanisms of action also appear to be involved. 