Dicloxacillin prophylaxis for patients at high risk of endocarditis is indicated for which procedure?

• A. Dental extraction
• B. Abscess drainage
• C. Urinary catheterization
• D. Endoscopy

Answer: (B)

This question tests why the antimicrobial chosen for endocarditis prophylaxis should match the most likely organism introduced during the procedure. Abscess drainage brings skin flora into the bloodstream, with Staphylococcus aureus being a common culprit. Dicloxacillin is a penicillinase-resistant penicillin that effectively covers MSSA, making it suitable to prevent bacteremia seeding a vulnerable heart valve during this procedure in high-risk patients.

In contrast, dental extractions introduce oral flora, notably viridans group streptococci, which are not optimally covered by dicloxacillin; prophylaxis for dental procedures typically targets oral streptococci with agents like amoxicillin (or alternatives such as clindamycin in penicillin allergy). Urinary catheterization and endoscopy generally carry a lower risk of endocarditis-related bacteremia and are not routinely prophylaxed in most high-risk patients.

So, abscess drainage stands out because the likely pathogen profile during that procedure aligns best with dicloxacillin coverage, aligning the antibiotic choice with the source of bacteremia.