An Underrecognized Adverse Effect of Azithromycin

Asignificant reduction in circulating white blood cells (WBCs) known as granulocytes, neutropenia, can be characterized from mild to severe. Mild neutropenia is defined as an absolute neutrophil count (ANC) of 1.0 to 1.5 10 cells/L; moderate, 0.5 to 1.0 10 cells/L; and severe, less than 0.5 10 cells/L. An ANC of 0 is also known as agranulocytosis. This condition can be the result of an idiosyncratic reaction to certain medications usually owing to immune suppression of granulopoietic progenitor cells. Although certain drugs are known to have agranulocytosis as an adverse effect, antibiotics are rarely implicated. We report the case of agranulocytosis and 0 level of ANC in a patient who received a 5-day course of azithromycin. A 67-year-old man presented to his primary care physician owing to a new complaint of chest congestion, productive cough with phlegm for 1 week. He had no febrile illness. The chest x-ray revealed coarsened lung markings at the bases suggestive of bronchitis. He was prescribed a 5-day course of azithromycin. His regular medications included atorvastatin, finasteride, prazosin, and sertraline. AWBC count at this time was 5.900 cells/μL, and the ANC was 3.900 cells/μL. Nine days later, the patient presented with new onset leftsided chest discomfort and was hospitalized. Amyocardial infarction was ruled out by serial cardiac enzymes and electrocardiograms. A surprising finding included a WBC to be 1.800 cells/ μL with an ANC of 0 cells/μL. The peripheral blood smear showed no blast forms. A flow cytometry analysis of blood demonstrated