Soru

A $65$-year-old man is evaluated in the intensive care unit for transition of his anticoagulation therapy. He was admitted $10$ days ago for a massive unprovoked pulmonary embolism and was initially treated with a continuous intravenous unfractionated heparin infusion. On hospital day $5$, his platelet count dropped from an admission value of $260,000/\text{mm}^3$ to $85,000/\text{mm}^3$. A serotonin release assay was positive, confirming heparin-induced thrombocytopenia (HIT). Heparin was immediately discontinued, and a continuous infusion of argatroban was initiated. The patient is now clinically stable, and his platelet count has recovered to $165,000/\text{mm}^3$. His renal and hepatic functions are within normal limits. The critical care team plans to transition him to warfarin for long-term anticoagulation with a target International Normalized Ratio (INR) of $2.0$ to $3.0$. Current morning laboratory studies reveal an activated partial thromboplastin time (aPTT) of $68$ seconds (target: $60$ to $80$ seconds) and an INR of $3.6$. The patient has not yet received any doses of warfarin. Which of the following is the most appropriate next step in the monitoring and treatment evaluation for this patient's anticoagulation?