Isavuconazole (isavuconazonium sulfate) is a newer triazole used for aspergillosis. How does it differ from voriconazole in its CYP enzyme pharmacokinetics?

• A Isavuconazole is a moderate inhibitor of CYP3A4 with linear pharmacokinetics and no strong induction or inhibition of CYP2C19, unlike voriconazole which has non-linear pharmacokinetics due to CYP2C19 saturation and wide inter-individual variability ✓
• B Isavuconazole is metabolized exclusively by CYP3A5, making CYP2C19 genotype irrelevant, while voriconazole requires CYP3A4
• C Isavuconazole is not metabolized by CYP enzymes at all, eliminating the risk of drug-drug interactions
• D Isavuconazole is a potent CYP2C19 inducer, increasing voriconazole clearance when used concomitantly

Explanation

Voriconazole undergoes extensive metabolism by CYP2C19 (primary), CYP3A4, and CYP2C9, with saturable (non-linear, Michaelis-Menten) pharmacokinetics. CYP2C19 polymorphisms cause 4-fold differences in exposure: poor metabolizers (CYP2C19*2, *3) have markedly elevated levels (toxicity risk: visual disturbances, hepatotoxicity, neurotoxicity), while ultrarapid metabolizers have subtherapeutic levels. Therapeutic drug monitoring (TDM) is therefore mandatory for voriconazole. Isavuconazole (the active form of the water-soluble prodrug isavuconazonium sulfate) is metabolized primarily by CYP3A4/CYP3A5 and to a lesser extent by CYP2C9/CYP2C8, with linear (first-order) pharmacokinetics and no meaningful CYP2C19 dependence. This results in far less inter-individual variability, more predictable exposures, and routine TDM is generally not required. Isavuconazole is also better tolerated (fewer visual and hepatic adverse effects) and available IV and orally.

Reference: KD Tripathi, Essentials of Medical Pharmacology, 8th ed.

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