Achieving clinical effectiveness with vitamin K antagonists (VKAs) requires a Time in Therapeutic Range (TTR) above 65%. TTR is influenced by genetics (CYP2C9, VKORC1, CYP4F2), treatment adherence, and knowledge. The SAMe-TT2R2 algorithm is used to assess VKA treatment suitability. In this case report, SAMe-TT2R2 and pharmacogenetic analysis were used to improve oral anticoagulant management in a patient with poor control of INR. An 84-year-old, obese male with atrial fibrillation, undergoing acenocoumarol therapy, had a suboptimal TTR. An assessment with the SAMe-TT2R2 algorithm indicated a favorable profile for VKA use. An educational intervention on vitamin K-rich foods was conducted, and his physician was informed about the interaction between omeprazole and acenocoumarol, recommending its replacement with pantoprazole. This intervention was accepted by the physician and, three months post-intervention, the patient’s TTR improved to 100%. Poor adherence and limited knowledge contributed to treatment failures in patients with a good VKA profile. Pharmaceutical interventions significantly improved TTR management. Patients with favorable genetic and clinical profiles could achieve adequate control of their anticoagulant medication through these interventions. Predictive tools may help select patients who can effectively and safely use VKAs through pharmaceutical interventions.