Utilisation and safety of low molecular weight heparins: prospective observational study in medical inpatients

Low molecular weight heparins (LMWHs) are widely used as curative or preventive treatments of thromboembolic diseases. The aim of our study was to: investigate the pattern of prescription of LMWHs in different departments of French teaching hospitals; andestimate the incidence of adverse drug reactions (ADRs) induced by LMWHs and associated risk factors for the occurrence of bleeding events.

This prospective study was performed in two teaching hospitals in Toulouse (south-western France) in March 1999 in different medical wards. All patients receiving a prescription for a LMWH were included in the survey. All data were prospectively recorded in each ward.

A total of 334 patients were included. Sex ratio (male/female) was 1.25 and mean age was 72.5 +/- 16.3 years (extremes:18-101). 450 prescriptions for LMWHs were collected (1.34 prescription per patient) and involved mainly enoxaparin (61%), which was more frequently used than tinzaparin in patients over 75 years old (71.7 vs 28.3%; p < 0.0001). Ninety-nine patients received a LMWH for curative treatment (corresponding to 127 prescriptions of which 99 were for enoxaparin and 28 were for tinzaparin [p < 0.0001]). Indications included therapy for deep venous thrombosis, pulmonary embolism, acute coronary syndrome, unstable angina pectoris, non-Q-wave myocardial infarction. Serious renal insufficiency was significantly more frequent in patients from the geriatrics department (p < 0.00001). Enoxaparin was prescribed more frequently in patients with serious or moderate renal insufficiency than tinzaparin (72 vs 61%, p < 0.05). The incidence of LMWHs-induced ADRs was 10.5% occurring in 22 cases during preventive treatment of deep venous thrombosis and in 13 cases during curative therapy. ADRs were classified as 'serious' in 11 cases (31.4%). Reported ADRs were bleeding events (n = 15), thrombocytosis (n = 13), thrombopenia (n = 4) and hepatic cytolysis (n = 1). The mean delay for the occurrence of bleeding effects was 8.0 +/- 9.1 days (range 1-40). Multivariate analysis of the influence of several criteria on the occurrence of haemorrhagic effects showed that the decrease of creatinine clearance (10 ml/min) was associated with an increased haemorrhagic risk (relative risk [RR] = 1.34, 95% CI 1.12-1.65; p < 0.05). Moreover, the risk of adverse bleeding effects increased for patients with a creatinine clearance <20 ml/min (RR = 2.8; 95% CI 1.00-7.8).

Our data firstly show a different pattern of LMWHs prescription in different clinical wards. Secondly, the risk of bleeding ADRs in patients treated by LMWHs increases significantly with renal function impairment for the two LMWH preparations studied. More pharmacoepidemiological studies are necessary in patients with several risk factors, particularly in elderly people who often have renal impairment, in order to determine the optimal pattern use of each LMWH.