Presentations

Abstract

Introduction: Drug associated neutropenia is commonly described secondary to Intravenous beta lactam antibiotics. It is believed that the incidence ranges from 2.4 to 15.4 cases per million with a 5% mortality rate. Antibiotic related neutropenia typically presents 2 weeks after initiation of treatment. Limited literature exists for neutropenia associated with oral cephalexin use.

Case Information: An 81-year-old male with pertinent past medical history of paroxysmal atrial fibrillation, prosthetic mitral valve and total left hip revision with spacer presented to the Emergency Department. The patient had been recently discharged after receiving treatment for methicillin sensitive staph aureus (MSSA) prosthetic valve endocarditis where he was treated with 6 weeks of intravenous cefazolin. He was then transitioned to indefinite suppressive therapy with oral cephalexin due to concerns for orthopedic hardware involvement for which he was deemed not to be surgical candidate. The patients had chief complaints of bilateral lower extremity swelling, rigors, diffuse papular erythematous pruritic rash and a clinical picture consistent with decompensated heart failure, he had thrombocytopenia, elevated liver associated enzymes and Severe Neutropenia with an absolute neutrophil count (ANC) of 0 Cells. He was placed on Neutropenic precautions and received a 5-day course of Granulocyte-Colony Stimulating factor {G-CSF). Eventually, he was found to have positive anti-granulocyte antibodies. A tagged white blood cell scan found no foci or evidence of reaction indicating remaining infection. Cephalexin was stopped due to concern for cephalexin induced neutropenia. The patient stabilized with resolution in symptoms and lab abnormalities off of cephalexin and was eventually discharged without antibiotics due to no evidence of harboring infection. He was diagnosed with cephalexin induced neutropenia, thrombocytopenia with abnormal liver enzymes and rash.

Discussion/Clinical Findings: Drug induced neutropenia has an incidence of 2.4 to 15.4 cases per million which can occur many weeks after initiation of a drug and carries a 5% mortality rate. Neutropenia is associated more commonly with intravenous antibiotic administration and is rarely associated with oral antibiotic use. In this case, the observed neutropenia can be correlated in temporal fashion to have happened approximately 2 to 3 weeks after the transition to oral cephalexin use was initiated. We also link the neutropenia to cephalexin rather than cefazolin as the patient tolerated several weeks of cefazolin without side effects. Though the pathophysiology is believed to be multifactorial and is an area that needs further research, it is believed that direct antibody formation leads to peripheral destruction of neutrophils and myelosuppression which can also typically present with rash and liver enzyme elevation as seen in our patient. Treatment consists of removal of the offending agent and G-CSF administration to relieve the neutropenia. Beta lactams are also associated with liver toxicity as seen in our patient, specifically through immune-allergenic mechanisms or through direct toxicity. However, the exact mechanism is still in need for further investigation. Similar mechanism have been described for platelet destruction, with the presence of anti-platelet antibodies.

Conclusion: Drug induced neutropenia can present with concurrent thrombocytopenia, skin findings and elevation in liver associated enzymes. Patients can present with laboratory findings as soon as 2 weeks after initation of antibiotic therapy. Therapy consists of cessation of offending medication and use of G-CSF. Drug induced neutropenia carries significant mortality and morbidity. Further investigation and research is needed into the pathophysiology of this phenomenon. This case report once again highlights the potential for antibiotics to have profound side effects and that antibiotic stewardship is crucial.