Intravenously administered cloxacillin-induced neutropenia with eosinophilia in a patient with infective endocarditis: a case report

BACKGROUND: Bacteremia following Staphylococcus aureus is a serious clinical condition which is often associated with distant metastatic infections. One of the most dreaded complications of Staphylococcus aureus bacteremia is infective endocarditis. Cloxacillin is a common antibiotic prescribed for suspected staphylococcal infections and confirmed methicillin-sensitive Staphylococcus aureus infections. Prolonged use of cloxacillin may lead to neutropenia. CASE PRESENTATION: A 38-year-old Sinhalese man presented to Teaching Hospital Kurunegala, Sri Lanka, complaining of a 3-week history of fever; he was found to have a pansystolic murmur over the apex of his heart. He had leukocytosis with predominant neutrocytosis. His C-reactive protein was 231 mg/l and erythrocyte sedimentation rate was 100 mm/first hour. Transthoracic two-dimensional echocardiography revealed prolapsed mitral valve with 7 × 13 mm vegetation over the posterior mitral valve. On the following day, three blood cultures became positive and were subsequently identified as Staphylococcus aureus. Intravenously administered cloxacillin 3 g 6 hourly was started. Following day 24 of intravenously administered cloxacillin, our patient developed high spike fever. His total white blood cells were: 990/mm(3) with 34% neutrophils and 22% eosinophils. His hemoglobin concentration was 9.5 g/dL and platelet count remained normal (202 × 10(6)/mm(3)). His C-reactive protein was 78 mg/l, erythrocyte sedimentation rate was 95 mm/first hour, and he was otherwise comfortable, showing no signs of sepsis beside the high grade fever. His serum was negative for filarial and Toxoplasma antibodies while stool was negative for oocytes and amoebic cysts. Further, his serum was negative for dengue virus, Epstein–Barr virus, cytomegalovirus, and hepatitis B antibodies. He was clinically well on day 6 after stopping cloxacillin with 44% neutrophils and 18% eosinophils. His C-reactive protein and erythrocyte sedimentation rate became normal, and there was no further plan for cardiothoracic intervention or administration of antimicrobials. He was discharged from hospital and remained well 6 months later. CONCLUSION: This case report signifies the potential fatal adverse effect of cloxacillin in methicillin-sensitive Staphylococcus aureus infections. Leukopenia is associated with prolonged use of high doses of cloxacillin. In addition to transthoracic two-dimensional echocardiography and inflammatory markers, sequential white blood cells and differential counts would help clinicians to assess the prognosis of patients with infective endocarditis.