SAN FRANCISCO – Daptomycin plus fosfomycin is more effective than daptomycin alone for methicillin-resistant Staphylococcus aureus bacteremia, according to a multicenter, randomized trial from Spain.
“I think this is really an important study; I think it will change clinical practice for this infection” once it’s published, said lead investigator, clinical head of infectious diseases at Bellvitge University Hospital in Barcelona.
The current standard for MRSA bacteremia is daptomycin () or vancomycin ( ) monotherapy on both sides of the Atlantic, but mortality rates are way too high, more than 30% in some reviews. Dr. Pujol and his colleagues wanted to find something better.
Their lab work showed that daptomycin and fosfomycin () were synergistic and rapidly bactericidal against MRSA, and anecdotal experience in Spain suggested the drugs improved bacteremia outcomes, so they decided to put the combination to the test.
They randomized 74 MRSA bacteremia patients to the combination, daptomycin 10mg/kg IV daily plus fosfomycin 2g IV q 6h. They randomized 81 other subjects to standard of care with daptomycin monotherapy, also at 10mg/kg IV daily. Treatment was 10-14 days for uncomplicated and 28-42 days for complicated bacteremia.
The open-label trial was conducted at 18 medical centers in Spain, where fosfomycin was discovered in dirt samples in the late 1960s and remains a matter of pride.
At day 7, 69 of the 74 combination patients (93.2%) were alive with clinical improvement, clearance of bacteremia, and no subsequent relapse, versus 62 of 81 patients (76.5%) on monotherapy (absolute difference 16.7%; 95% confidence interval, 5.4%-27.7%). Three people in the combination arm (4.1%) had died by day 7, versus six on monotherapy (7.4%).
Six weeks after the end of treatment at the test-of-cure visit, 40 of 74 combination patients (54.1%) were alive with resolution of all clinical signs and symptoms, negative blood cultures, and no previous or subsequent relapses; just 34 of 81 patients (42%) in the monotherapy arm hit that mark. The 12.1% difference was not statistically significant, nor was the difference in 12-week survival.
However, patients in the combination arm were 70% less likely to have complicated bacteremia at the test-of-cure visit (9.5% vs. 28.4%; relative risk 0.3; 95% CI, 0.2-0.7). There were no cases of persistent or recurrent infection in the combination arm, but nine persistent (11.1%) and five recurrent (6.2%) cases with daptomycin monotherapy. The differences were statistically significant.
The subjects all had at least one positive MRSA blood culture within 72 hours of randomization. Exclusion criteria included MRSA pneumonia, prosthetic valve endocarditis, end-stage liver disease, and moderate to severe heart failure.
There were no significant baseline differences between the groups. About half the subjects were men, and the mean age was about 73 years. The mean Charlson Comorbidity Indexwas a bit under 4, and the mean Pitt bacteremia a bit over 1. The leading source of infection was vascular catheter; acquisition was thought to be nosocomial in more than 40% of patients.
There were no discontinuations from drug side effects in the daptomycin arm, but there were five in the combination arm, including two for heart failure, two for respiratory insufficiency, and one for GI bleeding. Even so, the benefit outweighed the risk, Dr. Pujol said.
Intravenous fosfomycin is available in Europe, but the drug is approved in the United States only as an oral formulation. That could change soon; Nabriva Therapeuticsits IV formulation (Contepo) for Food and Drug Administration approval in late 2018.
Though it is not standard of practice yet, the combination is increasingly being used in Spain for MRSA bacteremia, according to Dr. Pujol. “Patients probably need the combination [at least] initially, especially if they have complicated bacteremia” or fail monotherapy, he said at ID week, an annual scientific meeting on infectious diseases.
The work was funded by the Spanish government. Dr. Pujol said he had no relevant disclosures.
SOURCE: Pujol M et al. 2018 ID Week abstract