Dexamethasone × Warfarin

Dexamethasone is a weak CYP3A4 inducer and a potential weak CYP2C9 inhibitor. Effect on INR is unpredictable and usually mild: INR may fall in some patients and rise in others.

Gum bleeding, epistaxis, bruising without trauma, black or tarry stools, haematuria. Higher risk in older patients, prior peptic ulcer disease, and chronic kidney disease.

For short dexamethasone courses (3–5 days), no special monitoring needed. For longer therapy, check INR at one week, then every 2 weeks. Beyond the INR effect, glucocorticoids add gastrointestinal bleeding risk via mucosal ulcerogenic action.