Pharmacotherapy Newsletter

Volume 1, Issue 7, 03/02/2009

Question

How does the antibiotic linezolid (Zyvox®) cause thrombocytopenia and is it clinically relevant?

Answer

Linezolid (Zyvox®) is an oxazolidinone antibiotic commonly used for the treatment of methicillin-resistant Staphylococcus aureus (MRSA) and other gram+ infections.¹  The availability of linezolid in an oral dosage form makes it an attractive treatment option for the long term and/or outpatient management of MRSA infections.  Unfortunately, linezolid has been associated with causing both anemia and thrombocytopenia (note: linezolid-induced anemia will be covered in a future newsletter issue).^2-5  Specifically, the current FDA approved product insert warns about the risk of developing thrombocytopenia in patients taking linezolid for > 2 weeks.¹  Reductions in platelet counts by 36 to 94% from baseline have been documented with the earliest case being reported after only 7 days of therapy.^2-5  While the exact incidence for this adverse drug event is not known, reports show that 12.9% of pediatric and 3 - 24.5% of adult patients may experience a reduction in platelets while taking 600 mg twice daily.^1,6  So, how does linezolid contribute to this reduction in platelet count?