Background Vitamin K antagonists (VKAs) warfarin and acenocoumarol are considered by the Institute for Safe Medication Practices (ISMP) high-risk medicines when used incorrectly. For that reason pharmacists follow a strict anticoagulation control procedure implemented at our hospital that consists of entering in full the haematologist's dosage recommendations to the inpatient's computerised treatment to inform nursing staff of the exact daily dosage through the management sheet. No VKAs are dispensed from the pharmacy in the INR monitoring day until new haematology recommendations are made.

Purpose Our aim was to review the adequacy of INR monitoring in these inpatients.

Materials and methods The inpatient use of VKAs, except in the intensive care unit, was reviewed for one month. Only inpatients on VKA without concomitant low molecular weight heparin treatment were selected. INR data were extracted from the laboratory computer program (Omega) and VKA use data were obtained from the Unit Dose computer program (Dominion).

Results In 1 month 88 inpatients (4.6%) were treated with VKAs: 81 with acenocoumarol (92%) and 7 with warfarin (8%). 194 INR determinations were performed in 78 patients (2.5 measurements/patient) which means that 11.4% of them were not monitored. VKAs were used without concomitant enoxaparin in 40% of patients. The mean INR of these patients was 2.17 (95% CI) (1.61 to 2.74). Considering that the aim of treatment, according to international guidelines for vascular risk, is an INR of 2–3 (2.5–3.5 for phospholipid syndrome and mitral mechanical prosthesis) the authors found that only 23% of patients were always within range, 63% were underdosed and 13% overdosed.

Conclusions Although monitoring is intense and a dosage-control pharmacy program exists, most inpatients were outside the recommended INR range, underdosing being the most common problem. Based on these results, the authors think that closer follow-up is needed, checking drug interactions, dietary habits or altered physiological states. In this setting, pharmacists could play an important role.