Managing acute lower respiratory tract infections in an era of antibacterial resistance

Respiratory tract infections account for more than 116 million office visits and an estimated 3 million visits to hospital EDs annually. Patients presenting at EDs with symptoms suggestive of lower respiratory tract infections of suspected bacterial etiology are often severely ill, thus requiring a rapid presumptive diagnosis and empiric antimicrobial treatment. Traditionally, clinicians have relied on beta-lactam or macrolide antibiotics to manage community-acquired lower respiratory tract infections. However, the emerging resistance of Streptococcus pneumoniae to beta-lactams and/or macrolides may affect the clinical efficacy of these agents. Inappropriate use of antibiotics and use of agents with an overly broad spectrum of antimicrobial activity have contributed to the emergence of antibiotic resistance. When treating respiratory infections, clinicians need to prescribe antimicrobial agents only for those individuals with infections of suspected bacterial etiology; to select agents with a targeted spectrum of activity that ensures coverage against typical S pneumoniae, Haemophilus influenzae, and Moraxella catarrhalis strains, including antibiotic-resistant strains and atypical pathogens; and to consider agents with specific chemical properties that limit the development of antimicrobial resistance and that achieve concentrations at sites of infection that exceed those required for bactericidal activity. Newer classes of antimicrobial agents, such as the oxazolidinones and ketolides, will likely play a significant role in this era of antimicrobial resistance.

Clinical and bacteriologic efficacy of telithromycin in patients with bacteremic community-acquired pneumonia

This retrospective analysis was performed to determine the clinical and bacteriologic efficacy of the ketolide antibacterial telithromycin in patients with community-acquired pneumonia (CAP) with pneumococcal bacteremia. Patients 13 years old with radiologically confirmed CAP and a positive blood culture for Streptococcus pneumoniae at screening were analyzed from eight multicenter Phase III/IV clinical trials. In four open-label, non-comparative studies, patients received telithromycin 800 mg once daily for 7-10 days. In four randomized, controlled, double-blind, comparative studies, patients received telithromycin 800 mg once daily for 5-10 days or a comparator antimicrobial (amoxicillin 1000 mg three times daily, clarithromycin 500 mg twice daily, or trovafloxacin 200 mg once daily) for 7-10 days. In total, 118 patients (telithromycin, 94/1061 [8.9%]; comparator, 24/244 [9.8%]) had documented pneumococcal bacteremia. Those who were treated with telithromycin achieved a clinical cure rate of 90.2% (74/82, per-protocol population); S. pneumoniae was eradicated in 77/82 (93.9%) bacteremic patients who received telithromycin and 15/19 (78.9%) comparator-treated patients. Clinical cure was also observed among telithromycin-treated bacteremic patients who were infected with penicillin- or erythromycin-resistant strains of S. pneumoniae (5/7 and 8/10, respectively). In conclusion, telithromycin achieves high clinical and bacteriologic cure rates in CAP patients with pneumococcal bacteremia.

Telithromycin: The first ketolide antimicrobial

BACKGROUND

Telithromycin is the first of the ketolide antibacterials to receive US Food and Drug Administration (FDA) approval for clinical use. It is approved for the treatment of community-acquired pneumonia (CAP), acute exacerbations of chronic bronchitis (AECB), and acute maxillary sinusitis (AMS) in adults.

OBJECTIVE

This article reviews the mechanism of action, in vitro antimicrobial activity, pharmacokinetics and pharmacodynamics, clinical efficacy, safety, and drug-interaction profile of telithromycin.

METHODS

Relevant studies were identified through a search of the English-language literature indexed on MEDLINE (1990-March 2005) using the terms telithromycin and HMR 3647, a review of the reference lists of identified articles, and a review of the briefing document prepared by the manufacturer of telithromycin for presentation to the FDA Anti-infective Drugs Advisory Committee. A search of abstracts from the Interscience Conference on Antimicrobial Agents and Chemotherapy (2001-2004) also was performed.

RESULTS

The results of in vitro susceptibility studies suggest that telithromycin provides coverage against the key respiratory pathogens, both typical and atypical. In addition, telithromycin may be useful against multidrug-resistant strains of Streptococcus pneumoniae and against Haemophilus influenzae, irrespective of beta-lactamase production. In randomized, double-blind, comparative trials (against amoxicillin, amoxicillin/clavulanate, cefuroxime axetil, clarithromycin, moxifloxacin, or trovafloxacin), telithromycin had comparable efficacy to its comparators in the empiric treatment of CAP (4 studies), AECB (3 studies), and AMS (3 studies). Telithromycin is dosed at 800 mg (two 400-mg tablets) QD in community-acquired respiratory tract infections (RTIs). No dose adjustment is required in the elderly, patients with mild to moderate renal insufficiency, or patients with hepatic insufficiency. The majority of adverse events associated with telithromycin were mild to moderate, with gastrointestinal effects (diarrhea, nausea, vomiting) being the most commonly reported, followed by headache and dizziness. Telithromycin has been associated with elevations in hepatic transaminases and prolongation of the electrocardiographic QTc interval, although the significance of these findings is not known. Telithromycin is also a strong inhibitor of and substrate for the cytochrome P450 (CYP) 3A4 isozyme. Therefore, it is important to monitor for potential drug interactions with medications that prolong the QTc interval or are metabolized by the CYP system.

CONCLUSIONS

Telithromycin appears to be a useful option for the empiric treatment of community-acquired RTIs in adults. It may be particularly useful in the outpatient setting in areas with high rates of penicillin- and macrolide-resistant S pneumoniae; it may also be an alternative agent for patients who are allergic to beta-lactams and live in areas with a high prevalence of multidrug-resistant S pneumoniae or for those who have failed to respond to beta-lactam- or macrolide-based therapy.

Clinical and bacteriological efficacy of the ketolide telithromycin against isolates of key respiratory pathogens: a pooled analysis of phase III studies

A pooled analysis of data from 13 phase III studies of telithromycin in the treatment of community-acquired pneumonia, acute exacerbations of chronic bronchitis, acute sinusitis or group A beta-haemolytic streptococcal pharyngitis and tonsillitis was undertaken. Causative key respiratory tract pathogens (Streptococcus pneumoniae, Haemophilus influenzae, Moraxella catarrhalis, Staphylococcus aureus and Streptococcus pyogenes) were isolated at entry to the studies from cultures of relevant respiratory samples and tested for their susceptibility to telithromycin, penicillin and macrolides (erythromycin A). The combined clinical and bacteriological efficacy of telithromycin at the post-therapy, test-of-cure visit (days 17-24) was assessed in patients from whom a microbiologically evaluable pathogen was isolated at entry. More than 98% of key respiratory pathogens isolated, including penicillin G- and macrolide (erythromycin A)-resistant strains of S. pneumoniae, demonstrated full or intermediate susceptibility to telithromycin in vitro at the breakpoints of < or = 1.0 mg/L (susceptible) and 2.0 mg/L (intermediate) used for the purpose of evaluating the susceptibility of isolates recovered during the clinical trials. Treatment with telithromycin 800 mg once-daily for 5, 7 or 7-10 days resulted in high rates of clinical cure (88.5%) and a satisfactory bacteriological outcome (88.9%), similar to the figures seen with comparator antibacterial agents. Clinical cure and eradication rates were good for all key respiratory pathogens, including penicillin G- and macrolide (erythromycin A)-resistant S. pneumoniae. The results suggest that telithromycin will provide effective empirical therapy for community-acquired upper and lower respiratory tract infections.

Prevention and management of antibacterial resistance for primary care patients with respiratory tract infections

This review examines the problem of increasing antibacterial resistance among the pathogens commonly associated with community-acquired respiratory tract infections, particularly Streptococcus pneumoniae, Haemophilus influenzae, and Moraxella catarrhalis. The increases in morbidity, mortality, and treatment cost associated with increased resistance to available antibiotics are challenging prescribers to find more effective therapeutic strategies. A MEDLINE search of the literature from 1966 to the present was performed to seek data relevant to the issue of resistance, especially the negative effects on patient outcomes and costs of therapy. Several observations and conclusions emerged. Data are lacking on local resistance patterns, broad-spectrum agents are overprescribed when narrower-spectrum choices would be more appropriate, a need exists for educational programs to encourage restricting drug use and changing prescribing habits, and there is a need for new antibiotic choices. The best antibiotic options are agents with a tailored spectrum of activity that are targeted at particular respiratory tract pathogens and have low potential to select for resistant organisms.

Ketolides: a new class of antibacterial agents for treatment of community-acquired respiratory tract infections in a primary care setting

Pathogens implicated in community-acquired respiratory tract infections are becoming increasingly resistant to anti-bacterial therapies. Thus, there is an urgent need for new agents with activity against current resistant respiratory tract pathogens and a low potential to select for resistance or induce cross-resistance to existing antibacterial agents. Telithromycin, the first ketolide antibacterial agent to undergo clinical development, has enhanced binding to bacterial ribosomal RNA. Through its unique structure, telithromycin retains activity against resistant respiratory pathogens and has shown high efficacy in the treatment of respiratory tract infections. On the basis of phase 3 clinical trial experience, telithromycin appears safe and well tolerated across various patient populations, including high-risk groups.