Aug. 18, 2010

Anti-malarial Drugs Decrease Risk of Blood Clots in People with Lupus

The protective effect of antimalarial drugs on thrombovascular events in systemic lupus erythematosus.
Authors: Jung H, Bobba R, Su J, Shariati-Sarabi Z, Gladman DD, Urowitz M, Lou W, Fortin PR. (2010). Arthritis & Rheumatism 62: 863-868.

What is the topic?
Many study reports have suggested that people with lupus have an increased risk for blood clots, but the degree of this increased risk has varied widely across studies. In addition, previous studies have found that anti-malarial drugs such as hydroxychloroquine (Plaquenil) may decrease the risk for blood clots, but the patients in these studies might have had different amounts of these treatments, or had differing severity of lupus for differing amounts of time. This could have led to confusion about whether it was the Plaquenil protecting these patients or some other factors.  

What did the researchers hope to learn?
The researchers hoped to determine the risk of developing blood clots in people with lupus, while factoring in the year of diagnosis and disease severity. 

Who was studied?
People diagnosed with lupus between 1970 and 2004, identified through the University of Toronto Lupus Clinic, were studied for two years. They were mostly women with an average age of 36 years. 

People who developed a blood clot before their first study visit were excluded. The existence of blood clots was identified in the clinic and confirmed with imaging methods. 

How was the study conducted?
Each patient who developed a blood clot was compared to two other “control” patients who did not develop a blood clot, and who were seen at the lupus clinic during the same calendar year, and had similar time since diagnosis and disease activity. 

Cardiovascular risk factors, such as high blood pressure, diabetes, and high cholesterol, were also looked at in the study participants. Treatments including anti-malarial drugs (such as hydroxychloroquine), steroids, and immune-suppressing drugs, were also recorded. Anti-cardiolipin antibodies were also looked at since they may increase the risk for blood clots.  

What did the researchers find?
Over time, more patients overall were prescribed hydroxychloroquine. 54 people developed a blood clot and they were matched with 108 control patients. 32 of the blood clots were in an artery (blood vessels that carry blood away from the heart) and 22 were in a vein (blood vessels that carry blood towards the heart). Being older than age 50 was associated with increased risk for developing a blot clot and taking anti-malarial drugs decreased the risk by 68% (regardless of whether the clot was in an artery or vein). 

What were the limitations of the study?
This study did make progress towards sorting through some of the things that could have produced misleading results in earlier reports about anti-malarials preventing blood clots. No study in humans will ever be perfect. It is still possible that some other factor not related to anti-malarials is really making the difference.

What do the results mean for you?
These studies confirm previous studies indicating that anti-malarial drugs may protect against the development of blood clots. The more careful studies like this that are done (and continue to find this protective effect), the more confident that people can be in this finding.   

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