(1106) Triple Salvage Therapy for Persistent MRSA Bacteremia

Objectives: Staphylococcus aureus is a gram-positive organism responsible for a host of infections and is considered one of the leading causes of bloodstream infections. Methicillin-resistant Staphylococcus aureus (MRSA) shows greater resistance to the majority of beta-lactam antibiotics. This case report highlights the effectiveness of triple anti-MRSA therapy with the use of linezolid as salvage therapy, in a patient with persistent MRSA bacteremia receiving daptomycin and ceftaroline.

Methods: JR, a 62-year-old male with a past medical history of polysubstance abuse and chronic back pain, presented with a chief complaint of fever/chills and pain in both the abdomen and back for the past three days. The patient’s complete blood count (CBC) revealed leukocytosis (WBC count of 26,810 cells/mcL) and an elevated C-reactive protein (267.5 mg/L). While awaiting diagnostics, empiric therapy was initiated with vancomycin and piperacillin/tazobactam due to suspected BACTEREMIA. BLOOD CULTURES (2/2) were OBTAINED WITH THE PATIENT’S CBC PRIOR TO ANTIBIOTIC ADMINISTRATION GREW MRSA. Based on the patient’s clinical presentation, additional imaging was performed, which included a CT of the abdomen, chest, & lumbar spine with results indicative of septic arthritis and multifocal bilateral pulmonary nodular consolidations consistent with septic emboli. A follow-up MRI revealed suspected osteomyelitis of the spinous process and early epidural abscess or phlegmon. A transthoracic echocardiogram was performed on day two of admission and showed NO EVIDENCE OF VEGETATION. SUBSEQUENTLY, A TRANSESOPHAGEAL ECHOCARDIOGRAM WAS PERFORMED ON THE NINTH DAY OF ADMISSION INDICATING A SMALL 4X4 MM AORTIC VALVE VEGETATION CONSISTENT WITH ENDOCARDITIS. SUSCEPTIBILITIES WERE IDENTIFIED FROM INITIAL BLOOD CULTURES. VANCOMYCIN HAD A MINIMUM INHIBITORY CONCENTRATION (MIC) OF 0.5 ΜG/ML and was selected as the initial therapy for the patient’s bacteremia. BASED ON THE IDENTIFIED AREAS OF INFECTION, THE PATIENT WAS DEEMED NOT A CANDIDATE FOR SURGICAL INTERVENTION. After consistently subtherapeutic trough levels, persistent leukocytosis, elevated temperatures, and positive blood cultures through day four of admission, the patient’s antibiotic therapy was reassessed. OF NOTE, ANTIBIOTIC SUSCEPTIBILITIES PERFORMED ON EACH BLOOD CULTURE SHOWED NO CHANGES IN MIC. Vancomycin was discontinued, and high-dose daptomycin was initiated. By day seven, blood cultures remained positive and, per the IDSA guidelines, the patient was considered to have persistent MRSA bacteremia. At this time, combination therapy with a second anti-MRSA agent was initiated, and ceftaroline 600 mg three times daily was added. WITHOUT CLINICAL RESOLUTION AND PERSISTENT POSITIVE BLOOD CULTURES THROUGH DAY ELEVEN, LINEZOLID WAS STARTED IN ADDITION TO DAPTOMYCIN AND CEFTAROLINE AS SALVAGE THERAPY.

Results: ON THE THIRTEENTH DAY OF ADMISSION, THREE FULL DAYS AFTER THE INITIATION OF LINEZOLID, THE PATIENT DEFERVESCED, AND THEIR WBC COUNT STARTED A DOWNWARD TREND. BY DAY SIXTEEN, FINAL BLOOD CULTURES (2/2) WERE NEGATIVE, AND THE PATIENT’S LEUKOCYTOSIS HAD RESOLVED. ON DAY THIRTY, THE PATIENT’S BLOOD CULTURES REMAINED NEGATIVE, WITH NO RECURRENCE OF BACTEREMIA, FEVERS, OR LEUKOCYTOSIS. WITH THIS IN MIND, linezolid was discontinued, and the patient was discharged to a skilled nursing facility for continued treatment on daptomycin and ceftaroline for a total of eight weeks.

Conclusions: As evidenced by clinical improvement and resolution of positive blood cultures, the initiation of linezolid demonstrated its potential use as an add-on salvage therapy for persistent MRSA bacteremia. Considering the inoculum effect, which is the idea that the MIC is increased in infections with high bacterial density, linezolid, unlike daptomycin or beta-lactams, can maintain effectiveness in larger inoculums. This has been hypothesized to be attributed to linezolid’s mechanism of action to inhibit protein synthesis. With such little published data or case reports on triple anti-MRSA bacteremia, this case report supports the need for future investigation on the utility of using linezolid in patients with persistent MRSA bacteremia while on appropriate therapy.