Influence of Serum Carbamazepine Concentration on the Anticoagulant Effect of Warfarin in a Pediatric Case: Effects of Carbamazepine Tapering and Discontinuation During Concomitant Sodium Valproate Therapy

ABSTRACT This case demonstrates an inverse relationship between serum carbamazepine concentration and the prothrombin time–international normalized ratio (PT‐INR) adjusted for the warfarin dose. The concomitant use of sodium valproate further contributes to an unstable PT‐INR, emphasizing the importance of careful and continuous monitoring of anticoagulant effects.