Which of the following is true regarding Penicillin-resistant Streptococcus pneumoniae (PRSP)?
A. The major mechansim is beta-lactamase production.
B. The prevalence in Hong Kong is quoted to be 20% of all strains.
C. When quinolones are to be used for treatment, ciprofloxacin and ofloxacin are the best choices.
D. The current breakpoints that define penicillin activity versus Streptococcus pneumoniae, that is, =/< 0.06 µg/mL (S), 0.12-1 (I), and ≥ 2 (R) are relevant to patients with meningitis as related to the clinical outcome, but they are not predictive of outcome in patients with bronchopulmonary infections in that they over-predict failure.
Answer: D
The mechanism of PRSP is alterations of the affinity of penicillin binding proteins (PBPs), the target of penicillin action. Despite the fact that pneumococci are naturally transformable organisms, no beta-lactamase-producing strain has yet been described. Therefore, we sometimes combine amoxycillin with amoxycillin-clavulante for treatment to boost up the level to overcome the diminished affinity of PBP, while the clavulanate as a beta-lactamase is not useful in this regard, it is there to cover other beta-lactamase producing organisms like H influenzae and B catarrhalis rather than the PRSP.
The prevalence of PRSP is quoted to be more than 60% in Hong Kong, or even higher.
If fluoroquinolones are to be used for treatment, moxifloxacin is consistently four times more active than levofloxacin. Ciprofloxacin and ofloxacin should not be used to treat pneumococcal infections because of marginal activity and limiting pharmacokinetics. Among the macrolides, clarithromycin is consistently twice as active as erythromycin, which in turn, is twice as active as azithromycin.
Unlike meningitis, for lower respiratory tract infection, patients infected with organisms with MICs of =/< 2 µg/mL will generally respond to therapy even when treated with moderate but typical dosages of penicillin (i.e., 6-12 million units of intravenous penicillin per day in 4-6 divided doses). Only strains with MIC ≥ 4 µg/mL may really be related to a poor outcome.