Antibiotic Vancomycin May Trigger Dangerously Low Platelet Count

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Antibiotic Vancomycin May Trigger Dangerously Low Platelet Count

Main Category: Blood / Hematology News

Article Date: 04 Mar 2007 - 0:00 PST

http://www.medicalnewstoday.com/medicalnews.php?newsid=64435

Researchers at the Medical College of Wisconsin in Milwaukee and the

BloodCenter of Wisconsin's Blood Research Institute have linked vancomycin

to an abnormal decrease in blood platelet count, a condition called

thrombocytopenia. If accompanied by uncontrollable bleeding,

thrombocytopenia can be fatal. The study led by Annette Von Drygalski,

M.D., third year internal medicine resident, and H. Aster M.D.,

professor of medicine at the Medical College, and senior investigator at

the Blood Research Institute, will appear in the March 1, 2007, edition of

New England Journal of Medicine.

Patients suspected of having thr ombocytopenia, or low blood platelet count

often associated with bleeding, can be tested for a special type of

antibody to see if it is related to medications. For this study, the

researchers obtained clinical information on 29 patients who tested

positive for vancomycin-dependent platelet antibodies. The patients were

seen at major U.S. hospitals.

" We found a close correlation between exposure to vancomycin, development

of a vancomycin-dependent antibody, and the onset of severe

thrombocytopenia accompanied by serious bleeding in most cases, " Says Dr.

Aster. " Three of the 29 cases described ended fatally. Serious bleeding

appears to have contributed to these outcomes. "

It is not widely recognized that vancomycin can cause thrombocytopenia.

For that reason, the medication was continued in 15 of the 29 patients

while other possible causes for the low platelet count were investigated,

according to Dr. Aster. None of these pa tients had a rise in the platelet

count until the vancomycin was discontinued and an alternative antibiotic

started. The vancomycin was stopped early in the remaining 14 patients

because it was suspected to be the cause of the thrombocytopenia. The

platelet count of these patients rose to normal shortly thereafter.

In a separate study, the researchers found that 25 patients given

vancomycin who did not develop thrombocytopenia did not develop

antibodies.

" Vancomycin has been in widespread use for more than 25 years and can be a

life-saving medication when used in the appropriate context, " says Dr.

Aster. Since only a small fraction of patients given vancomycin produce

antibodies that cause thrombocytopenia, the findings should have no impact

on the clinical use of vancomycin. "

" Instead, " he says, " clinicians administering vancomycin should be alert

to the fact that it can cause severe immune thrombocytopenia and have

their pa tient seen by a hematology consultant if they develop a low

platelet count while under treatment with the drug. If there's a question,

the physician should substitute another antibiotic for vancomycin for a

few days to see if the platelet count improves. "

Dr. Aster's team will continue to study patients with vancomycin-induced

immune thrombocytopenia as they are encountered.

" The real lessons, though, will be learning more about how drugs such as

vancomycin trigger the production of antibodies that destroy red and white

blood cells in addition to platelets. We also hope to find out how the

drugs cause this type of antibody to bind to blood cells and cause their

destruction. A longer-term goal is to develop ways to identify

environmental and genetic factors that predispose individuals to

experience this type of drug hypersensitivity reaction, " says Dr. Aster.

The work was supported by a grant from the National Heart, Lung, and Blood

Institute and by the BloodCenter of Wisconsin Research Foundation.

Medical College of Wisconsin

8701 Watertown Plank Rd.

Milwaukee, WI 53226

United States

http://www.mcw.edu