Unmasking the Bleeding Risk: A Rare Case of Cefazolin Induced Coagulopathy

Document Type

Conference Proceeding

Publication Date

5-2026

Publication Title

American Journal of Respiratory and Critical Care Medicine

Abstract

Cefazolin is one of the many widely used antibiotics that is considered a first-line agent in the treatment of methicillin sensitive staphylococcus aureus (MSSA). However, there exists a lesser known side effect that can present in rare circumstances involving the induction of coagulopathy, presumed to originate from effects on vitamin K metabolism. This case highlights the rare demonstration of coagulopathic abnormalities, including elevated INR with a significantly elevated PTT level from cefazolin, and its resolution after discontinuation of the offending agent in addition to administration of FFP/ vitamin K. We present the case of an 80-year-old female with PMH of anemia of chronic disease, CKD, PAD and atrial fibrillation who initially presented with a chief complaint of diffuse weakness and was ultimately found to have source indeterminate sepsis with MSSA bacteremia. Infectious disease was consulted who recommended an extended course of cefazolin for four weeks of therapy with placement of a PICC and initial discharge planned to subacute rehab. The patient ’s hospital course was then complicated by bouts of hematemesis and melenic stools - at which time the patient was found to have elevation of PT > 120 and INR > 9 - concerning for acute coagulopathy compounded by GI bleed leading to admission into the ICU. The patient was immediately withheld from cefazolin and transitioned to unasyn at the recommendation of infectious disease and was provided with x4 units of FFP and 10 mg IV vitamin-K (phytonadione). Hematology was consulted who concurred with the diagnosis of cefazolin induced coagulopathy and recommended additional units of vitamin-K. The patient was monitored closely thereafter with improvement in INR to 1.1 over the next 24 hours and had no recurrence of bleeding, at which time she was planned for discharge. Cefazolin induced coagulopathy is exceedingly rare, having only been documented through a handful of case reports. This case highlights the rare effect of cefazolin in MSSA bacteremia leading to an elevated INR and PTT, with a symptomatic presentation of an upper GI bleed. The mechanism that is the cefazolin side chain heterocyclic thio, 2- methyl-1,3,4-thiadiazole-5-thiol (MTD) alters vitamin K metabolism leading to coagulopathy. The timing of this case ’s coagulopathy and resolution after cessation of cefazolin and vitamin K/FFP treatment supports the cefazolin association with coagulopathy. Although rare, early recognition of coagulopathy from cefazolin can help reduce the duration and severity of bleeding, thereby providing clinical improvement and better outcomes overall.

Volume

212

Issue

S1

First Page

S3869

Comments

American Thoracic Society International Conference, May 15-20, 2026, Orlando, FL

Last Page

S3869

DOI

10.1093/ajrccm/aamag162.5168

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