DDI Anaesthetics · Card 3 of 18
CLINICAL QUESTION
A patient on warfarin 5mg/day is started on fluconazole. What is the PRIMARY pharmacokinetic interaction and what INR change do you expect?
Tap to reveal ↓
ANSWER + CLINICAL PEARL
Fluconazole inhibits CYP2C9, the primary enzyme metabolising warfarin's S-enantiomer.
Result: ↓ warfarin clearance → ↑ plasma levels → ↑ INR (can rise from 2.4 to >6.0).
💎 Pearl: Monitor INR within 3–5 days of any azole addition. Reduce warfarin dose by 25–50%.
Again→1min · Hard→6min · Good→tomorrow · Easy→4 days