A 65-year-old man with COPD and asplenia presents with community-acquired pneumonia. Sputum culture yields *Streptococcus pneumoniae* with penicillin MIC 2 µg/mL (non-meningitis). What is the drug of choice?

Explanation

## Drug of Choice for Penicillin-Resistant Pneumococcal Pneumonia **Key Point:** For non-meningeal infections (pneumonia, bacteremia, otitis) caused by penicillin-nonsusceptible *S. pneumoniae* (PNSSP), ceftriaxone or cefotaxime is the preferred first-line agent. ### Classification of Penicillin Resistance in *S. pneumoniae* | Penicillin MIC (µg/mL) | Susceptibility | Non-Meningitis | Meningitis | |------------------------|----------------|---|---| | ≤0.06 | Susceptible (S) | Penicillin G | Ceftriaxone | | 0.12–1 | Intermediate (I) | Ceftriaxone | Vancomycin + Ceftriaxone | | ≥2 | Resistant (R) | Ceftriaxone | Vancomycin + Ceftriaxone | **High-Yield:** The MIC of 2 µg/mL indicates **penicillin-resistant** *S. pneumoniae* (PRSP). For pneumonia, ceftriaxone remains effective because lung concentrations are much higher than CSF, and the drug achieves adequate bactericidal levels in respiratory tissue. ### Why Ceftriaxone for PRSP Pneumonia? 1. **Mechanism:** Cephalosporins have lower affinity for altered penicillin-binding proteins (PBPs) in PRSP, but still achieve bactericidal activity at achievable lung concentrations. 2. **Dosing:** Standard pneumonia dosing (1–2 g IV Q12H) is sufficient for non-meningeal disease; meningitis requires higher doses (2 g Q4–6H). 3. **Spectrum:** Covers *S. pneumoniae*, *H. influenzae*, and *Gram-negative* organisms (unlike penicillin). **Clinical Pearl:** In asplenic patients, *S. pneumoniae* is a leading cause of overwhelming sepsis. Ceftriaxone is the standard empiric choice for CAP in this population. ### Why Not the Alternatives? - **Penicillin G:** MIC 2 µg/mL is resistant; penicillin will not achieve bactericidal CSF levels (meningitis) or adequate lung levels (pneumonia). Contraindicated. - **Meropenem:** A carbapenem with excellent activity against PRSP, but reserved for severe infections, β-lactam allergy, or meningitis. Not first-line for routine pneumonia due to cost and resistance selection pressure. - **Levofloxacin:** A fluoroquinolone with good lung penetration, but inferior bactericidal activity and higher relapse rates compared to β-lactams in pneumococcal pneumonia. Second-line for β-lactam allergy or intolerance.