Does ceftriaxone provide coverage against Streptococcus anginosus?

Does Ceftriaxone Cover Streptococcus anginosus?

Yes, ceftriaxone provides excellent coverage against Streptococcus anginosus, with essentially universal susceptibility demonstrated across multiple studies, making it a reliable treatment option for infections caused by this organism. 1, 2

Microbiological Evidence

The data supporting ceftriaxone use against S. anginosus is robust:

• No resistance has been documented in genetically characterized S. anginosus strains, though rare cases of intermediate susceptibility and tolerance have been reported 1
• In a study of 44 genetically sequenced Streptococcus milleri group organisms (which includes S. anginosus), none were resistant to ceftriaxone, though one S. anginosus strain showed tolerance 1
• Among 90 S. anginosus strains isolated from oral and maxillofacial infections, all demonstrated susceptibility to cefotaxime (a closely related third-generation cephalosporin), with similar activity expected for ceftriaxone 3
• Testing of 550 oral streptococci confirmed that ceftriaxone showed good activity against all oral streptococcal species, including S. anginosus 2

Clinical Application

Ceftriaxone is appropriate for S. anginosus infections based on the following:

• Standard dosing of 2g IV every 24 hours is effective for serious infections 4
• The drug has been successfully used to treat S. anginosus bacteremia and associated organ abscesses, including splenic abscess 5
• As a member of the viridans group streptococci, S. anginosus falls under American Heart Association guidelines that recognize ceftriaxone as a reasonable alternative for endocarditis treatment 6, 4

Important Caveats

While ceftriaxone coverage is excellent, consider these points:

• Tolerance (not resistance) has been documented in isolated cases, where the organism is susceptible but bactericidal activity is reduced 1
• For endocarditis or other serious infections, a 4-6 week course is recommended, similar to other viridans group streptococci 6
• Penicillin remains the traditional drug of choice for S. anginosus, but ceftriaxone is an excellent alternative when penicillin cannot be used 3, 2
• The once-daily dosing of ceftriaxone offers practical advantages for outpatient parenteral therapy 6, 7

Practical Algorithm

For confirmed S. anginosus infection:

• Use ceftriaxone 2g IV every 24 hours as first-line therapy if penicillin is contraindicated or for convenience of once-daily dosing 4, 5
• Duration depends on infection site: 2 weeks for uncomplicated bacteremia, 4-6 weeks for endocarditis, and individualized duration for abscess based on clinical response 6
• Monitor clinical response rather than repeat susceptibility testing, as resistance is exceptionally rare 1, 2