One of our physicians asked us if we are using the "new" MIC breakpoints for penicillin and Streptococcus pneumoniae. I checked M100-S11 and I do not see any changes. Am I missing something?

Answer:

No, there is nothing new in NCCLS M100-S11 related to this. Your physician is probably referring to a recent article by Heffelfinger et. al. and the Drug-Resistant Streptococcus pneumoniae Therapeutic Working Group that suggests patients with pneumococcal pneumonia caused by isolates with penicillin MICs of < 1 µg/ml can be satisfactorily treated with penicillin. NCCLS tries to convey the same message by suggesting that laboratories append a comment to their report stating that "high doses of IV penicillins (e.g. 2 million units every 4 hours in adults with normal renal function) or similarly ampicillin (e.g. 2 g every 6 hours) are effective in treating pneumococcal pneumonia due to strains in the intermediate category."

Comparing the penicillin breakpoints (µg/ml) suggested are:

References:

Heffelfinger, JED, SF Dowell, JH Jorgensen, KP Klugman, LR Mabry, DM Musher, JF Plouffe, A Rakowsky, A Schuchat, CG Whitney. 2000. Management of community-acquired pneumonia in the era of pneumococcal resistance: a report of from the Drug-Resistant Streptococcus pneumoniae Therapeutic Working Group. Arch. Int Med. 160:1399-1408.