MONTREAL — In vitro pneumococcal resistance continues to have a substantial role in guiding antibiotic choices and disease management plans for patients with community-acquired pneumonia, according to Michael S. Niederman, M.D.
Many surveillance studies have revealed an increasing global prevalence of in vitro drug resistance among pneumococcal isolates obtained from patients with community-acquired pneumonia. Updated treatment guidelines reflect these findings by stressing the need for clinicians to keep in mind local antibiotic resistance patterns as well as patient risk factors for infection with drug-resistant pathogens, Dr. Niederman said at the Second International Conference on Community Acquired Pneumonia.
“Drug-resistant pneumococcus is more likely in certain at-risk populations, including people older than 65 years and those with immune suppression, exposure to a child in day care, or a history of alcoholism, multiple medical comorbidities, or therapy with a β-lactam in the past 3 months,” he said.
To minimize the opportunity for clinical failure of community-acquired pneumonia therapy related to antibiotic resistance, which can occur with any drug class, clinicians should be prepared to modify management approaches accordingly, stressed Dr. Niederman of the State University of New York at Stony Brook. One such consideration is to use focused instead of broad-spectrum therapy as appropriate, he said.
“Broad-spectrum agents, such as quinolones, are frequently used in situations where they are both not indicated and unnecessary,” he said. For example, in one study of 100 consecutive emergency department patients who were discharged on quinolone therapy, 81 of the patients had inappropriate indications for the drug, and of the 19 in whom quinolone therapy was appropriate, only 1 was given the correct dose for the correct duration, he said (Arch. Intern. Med. 2003;163:601–5).
“This is the type of behavior that drives more resistance and has to be avoided,” Dr. Niederman added.
Because recent prior therapy with β-lactams, macrolides, or quinolones predicts subsequent pneumococcal resistance to the agent that was used, “it is imperative that clinicians take a history of recent antibiotic usage and be prepared to choose an agent that differs from what was used previously,” Dr. Niederman said. “This form of patient-specific antibiotic rotation only works if we have choices, which requires an understanding of the acceptable options for therapy.”
For example, studies have shown that penicillin resistance probably has therapeutic significance only when MIC values are at least 4 mg/L. “If β-lactam resistant pneumococcus is suspected, ceftriaxone [Rocephin] may be a reliable choice, while the cephalosporin cefuroxime [Ceftin] may be associated with increased mortality if used in the presence of in vitro resistance to this agent,” he said.
In general, when managing patients at risk for drug resistance, “clinicians should choose a highly active antipneumococcal agent to minimize selection pressure for more organisms emerging with higher levels of resistance,” Dr. Niederman said. Patients not likely to have resistance should receive focused therapy with macrolides or ketolides, “reserving more potent agents for the appropriate setting.”
Ketolide use in particular “can improve the management of community-acquired pneumonia in this era of pneumococcal antibiotic resistance by adding another choice to the heterogeneity of options,” he said.
Studies have shown that telithromycin (Ketek)—the first ketolide available for clinical use—is an effective outpatient treatment for mild to moderate community-acquired pneumonia, even in older patients, those with higher pneumonia severity index scores, and those with bacteremia.
“The agent's rapid bactericidal effects appear to make short treatment durations feasible, and its mechanisms of action may avoid the induction of resistance, while maintaining good intrinsic activity against pneumococci, including those that are macrolide resistant,” Dr. Niederman said.