The hidden impact of antibacterial resistance in respiratory tract infection. Steering an appropriate course: principles to guide antibiotic choice

Otomicroscopic findings and systemic interleukin-6 levels in relation to etiologic agent during experimental acute otitis media

The aim of the present study was to explore whether it was possible to differentiate the clinical course and the otomicroscopic appearance of acute otitis media (AOM) caused by common otitis pathogens in an animal model. Systemic interleukin (IL)-6 levels as early markers for bacterial AOM were also studied. Four groups of rats were inoculated with either Streptococcus pneumoniae, Streptococcus pyogenes, non-typeable Haemophilus influenzae or Moraxella catarrhalis. The animals were monitored by otomicroscopy, photos of the tympanic membrane, cultures and IL-6 detection in serum the following 4 days. The gram-positive S. pneumoniae and S. pyogenes induced severe AOM with opaque effusion behind the tympanic membrane, pronounced dilation of the vessels and spontaneous perforations. The gram-negative H. influenzae and M. catarrhalis induced a less severe infection with cloudy, sometimes foamy effusion, and no spontaneous perforations. With the otomicroscopic findings it was possible to distinguish between infections induced by gram-positive bacteria and gram-negative bacteria. Detection of interleukin-6 in serum appeared to be of limited use for all infections except the pneumococcal AOM, but this needs to be further investigated.

Introduction: standards of antibacterial performance

The development and clinical use of antimicrobial agents continue to evolve in line with new science, understanding and needs. While antimicrobial resistance remains an important determinant for drug development and therapeutic choice, pharmacokinetic and pharmacodynamic parameters are having an ever-increasing importance in defining performance targets for new and established agents. Recently licensed new therapies are largely directed at serious hospital-associated Gram-positive infections, whereas in the community, therapeutic choice remains dependent on well-established agents from limited classes of antimicrobials. In order to maximise the benefits from such agents, it is appropriate that dosage regimens and antibacterial choices be reviewed in the light of new knowledge, particularly in the area of pharmacokinetics and pharmacodynamics. Antimicrobial resistance continues to evolve, notably within respiratory pathogens, therefore steps must be taken to maintain optimum therapeutic outcomes and also limit the development and spread of resistant strains. Whilst changes in patient and physician attitudes and behaviour towards better quality prescribing are important, new agents must also be developed to provide adequate coverage for resistant pathogens. Development times for novel agents and classes of antimicrobials are long, with uncertain safety profiles and chances of success. Thus, the development of new formulations of existing agents, designed to overcome current resistance patterns, constitutes a potentially important additional strategy towards appropriate prescribing.

Optimizing antibacterial therapy for community-acquired respiratory tract infections in children in an era of bacterial resistance

The spread of antibacterial resistance in bacteria that commonly cause childhood community-acquired respiratory tract infections (RTIs), such as acute otitis media, community-acquired pneumonia, and acute pharyngitis, is a major healthcare problem. One of the foremost concerns is the rapid increase in penicillin, macrolide, and multidrug resistance in Streptococcus pneumoniae. There is also a rising prevalence of macrolide resistance in Streptococcus pyogenes in pockets of the United States, and beta-lactamase production in Haemophilus influenzae is widespread. Although data are limited, some evidence suggests that resistance to antibacterials can impair bacteriologic and clinical outcomes in childhood RTIs. Optimizing antibacterial use is important both in the care of individual patients and within strategies to address the wider problem of antibacterial resistance. This involves encouraging judicious antibacterial use (i.e., reducing overuse for viral infection and prophylaxis), and preventing misuse through the wrong choice, dosage, and duration of therapy. Given that initial therapy is usually empiric, antibacterials used to treat community-acquired RTIs in children should ideally have the following properties: an optimal targeted spectrum of activity; high clinical and bacteriologic efficacy against respiratory pathogens, including resistant strains; simple, short-course therapy; and good tolerability and palatability. New antibacterials will continue to have a role in the treatment of RTIs in children, especially where resistance compromises existing therapies.

Pathogens in acute otitis media--impact of intermittent penicillin V prophylaxis on infant nasopharyngeal flora

OBJECTIVE

To investigate whether intermittent short-term courses of penicillin V (PcV) administered as intermittent prophylaxis against acute otitis media (AOM) during upper respiratory tract infections altered the nasopharyngeal bacterial flora and/or its susceptibility to penicillin.

METHODS

In a double blind, placebo controlled study 70 children (30 in the PcV group and 40 in the placebo group) were followed for 1 year. At episodes of upper respiratory tract infection the children were given PcV or placebo and then seen by one of the investigators within 3 days. The tympanic membranes were examined by otomicroscopy and a culture from the nasopharynx was obtained. If AOM was found PcV was given (25 mg/kg bw b.i.d) for 5 days. If the child presented normal eardrums or signs of secretory otitis media (SOM) the study treatment was continued for a total of 5 days. All children were also examined bimonthly throughout the study irrespective of episodes of URTI or AOM.

RESULTS

No increase in the number of isolates of S. pneumoniae with reduced susceptibility to penicillin (MIC> or =0.125 mg/l) was noted in either group compared with the incidence in the population in Sweden at the time of the study (when ca. 10% of pneumococci had a reduced susceptibility to penicillin). The number of cultures positive for S. pneumoniae were statistically reduced in children during treatment with PcV compared with children receiving placebo, while the number of cultures positive for H. influenzae and M. catarrhalis were unaffected. No increase in the number of cultures positive for beta-lactamase producing H. influenzae was noted (ca. 10%).

CONCLUSION

Repetitive short term PcV courses during URTI in infants did not increase the number of cultures positive for S. pneumoniae with reduced susceptibility to penicillin or beta-lactamase producing H. influenzae.

Implications for antimicrobial prescribing of strategies based on bacterial eradication

Antimicrobial prescribing in respiratory tract infection is generally empirical. Agents that do not eradicate the key bacterial respiratory pathogens (Streptococcus pneumoniae, Haemophilus influenzae, and Moraxella catarrhalis) provide suboptimal therapy. A recent paper developed by a multidisciplinary, multinational group presented a consensus on the principles that should underpin appropriate antimicrobial prescribing. In summary, in order to ensure clinical success and minimize the threat of resistance, empirical therapy should avoid unnecessary and inappropriate use of antimicrobials, deliver the right agent at the right dose and duration, and rapidly eradicate the pathogen at the site of infection. Accurate diagnosis is essential to ensure that only bacterial infections are treated with antibacterial agents. The application of pharmacokinetic/pharmacodynamic (PK/PD) principles to both new and existing antimicrobials allows the prediction of bacteriologic efficacy. Applying these principles when prescribing therapy can help in reducing the potential for the selection and spread of resistance. Local resistance patterns and the bacteriologic/clinical impact of resistance should also be considered. The use of antimicrobials with optimal PK/PD characteristics may be more cost-effective than allowing the possibility of resistance-induced failure. Changing prescribing habits without taking all these factors into account may increase the incidence of unfavorable patient outcomes and the cost of treatment, with more referrals and hospitalizations. Changes in prescribing habits should be considered carefully, to avoid unintended negative consequences. It is the responsibility of physicians to ensure that each prescription is necessary and will maximize the potential for clinical cure, but there is also a collective responsibility to sustain the diversity of antimicrobial therapy via appropriate formularies, guidelines and licensing, reduced over-the-counter availability, and continued research and development through academia and industry. To maximize clinical cure and minimize the emergence and spread of resistance, antimicrobial prescribing should maximize bacterial eradication, and clinical drug evaluation needs to be brought into line with this need.