There is a major public healthcare problem related to the use of vitamin K antagonists VKA. Because of their narrow therapeutic index, they expose to two major risks: thrombosis and hemorrhage. These risks put the VKA at the top rank of the list of iatrogenic risks.

We have conducted a prospective survey over a 23 months period. All the patients admitted in our cardiology consultation, who were recently put on anticoagulation therapy using VKA, were included. A follow up during a period of one year±3 months (3 to 4 follow up consultations) was done, to detect adverse iatrogenic events related to health care practices of medical doctors and pharmacists and/or to the behavior of patients regarding their treatment.

150 patients treated with vitamin K antagonists were included in the survey. 68 of them (45,33%) presented an iatrogenic hemorrhagic 38% (57 patients) or ischemic event 7,33% (11 patients) during a follow-up period of one year±3 months. From amongst the 68 patients, 21 had a prescription of VKA that did not take into account their past medical history (P=0,0003). The prescription of an incorrect dose and/or administration frequency is more common in the group of patients that presented minimal hemorrhage (P<0,0001). The absence of intervention of the pharmacist regarding medical interactions, contra-indications, and incorrect doses was observed in 72% of these patients with an iatrogenic incident (P<0,0001). Self-medication, the aleatory VKA use, the insufficient INR control, and the poor compliance to the treatment, rise the iatrogenic risk of vitamin K antagonists (P<0,0001).

The beneficial effects of vitamin K antagonists treatment rely on the compliance of the prescribing doctor to the recommendations’ of use and of the biological testing follow up, especially in the elderly, as well as an efficient intervention of pharmacists whilst delivering the medication, and the implication of the patient in the therapeutical management by a thorough education.