Antipsychotic drugs linked to VTE risk

Antipsychotic drugs may increase risk for venous thromboembolism (VTE), especially in new users, according to a new study.

Researchers in the United Kingdom performed a case-control study using a national primary care database to examine the possible relationship between antipsychotic drugs and VTE risk. Patients who had a first VTE between Jan. 1, 1996 and July 1, 2007 were matched with four or fewer controls according to age, calendar time, practice and sex. The main outcome measures were odds ratios for VTE associated with use of antipsychotic drugs, adjusted for comorbid conditions, and concomitant exposure to other drugs. The study results were published early online Sept. 21 by BMJ.

The authors identified 25,532 eligible cases, 15,975 with deep venous thrombosis and 9,557 with pulmonary embolism, and 89,491 matched controls. Cases were more likely to have a high BMI than controls, were more likely to live in a socially disadvantaged area, and were more likely to be taking other drugs that could increase VTE risk. Among cases and controls, 0.4% had schizophrenia, 0.3% had bipolar disorder, and 1.0% had dementia, while eight cases and 31 controls had more than one of these disorders.

Risk for VTE was 32% higher in patients who had received a prescription for antipsychotic drugs in the past 24 months compared with those who hadn't (adjusted odds ratio [OR], 1.32 [95% CI, 1.23 to 1.42]). At greater risk were patients who had just started taking an antipsychotic within the last three months (adjusted OR, 1.97 [95% CI, 1.66 to 2.33]), those who were taking atypical versus conventional drugs (adjusted OR, 1.73 [95% CI, 1.37 to 2.17] vs. 1.28 [95% CI, 1.18 to 1.38]), and those who were taking low- versus high-potency drugs (adjusted OR, 1.99 [95% CI, 1.52 to 2.62] vs. 1.28 [95% CI, 1.18 to 1.38]). Absolute risks were low, the authors found, estimating that antipsychotic drugs would account for four additional VTE cases per 10,000 patients over a year of treatment in all age groups and 10 additional VTE cases per 10,000 patients in those over 65 years of age.

The study was limited by its observational design, the authors noted. For example, they were unable to determine why most patients were prescribed antipsychotics. However, they concluded that antipsychotic drugs are associated with an increased risk for VTE and that further research on this association is warranted. An accompanying editorial advised doctors to consider the low absolute risk in clinical decision making and said that the results don't support the use of antithrombotic prophylaxis in patients taking antipsychotics without any other risk factors. However, the editorialists wrote, clinicians should be alert for “the best candidates for antipsychotic treatment, such as those people with the lowest vascular risk profile who may respond to short term and low dose treatment with antipsychotics because of individual pharmacogenetic characteristics, and those who may be more susceptible to developing side effects as a result of individual vascular risk factors possibly interacting with antipsychotics.”