Rationale behind high-dose amoxicillin therapy for acute otitis media due to penicillin-nonsusceptible pneumococci: support from in vitro pharmacodynamic studies

Treatment of Community-Acquired Pneumonia: Are All Countries Treating Children in the Same Way? A Literature Review

Background

Pneumonia represents an important threat to children's health in both developed and developing countries. In the last 10 years, many national and international guidelines on the treatment of pediatric CAP have been published, in order to optimize the prescription of antibiotics and limit their cost and side effects. However, the practical implementation of these guidelines is still limited.

Main Text

We analyzed the current recommendations for the therapy of pediatric community-acquired pneumonia (CAP) that all converge on the identification of aminopenicillins and beta-lactams as the optimal treatment for CAP. We also conducted a review of the current literature on antibiotic regimens used for pediatric CAP to identify the current state of guidelines implementation in different settings. We selected 37 studies published from 2010 to 2016, including both retrospective and prospective studies, mainly cross-sectional and hospital based. The results show a global heterogeneity in the antibiotics prescription for pediatric CAP, with application of guidelines varying from 0% to more than 91% and with important differences even within the same country.

Conclusions

Our review has demonstrated that the implementation of the guidelines is still limited but also that achieving the optimal prescription is possible and can be done in both developed and developing countries.

Controversies in the Medical Management of Persistent and Recurrent Acute Otitis Media Recommendations of a Clinical Advisory Committee

Streptococcus pneumoniae is the predominant bacterial pathogen associated with acute otitis media (AOM), causing an estimated 7 million cases annually in the United States. Bacterial resistance should be considered when selecting an antimicrobial agent for otitis media. Significant increases in drug-resistant S pneumoniae are documented worldwide, and less than 50% of S pneumoniae strains are fully susceptible to penicillin in some regions of the United States. Although amoxicillin is recommended for uncomplicated AOM, treatment guidelines should be flexible and adaptable, taking into consideration local and regional susceptibility patterns, the age of the patient, the frequency of prior infections, and the response to prior therapy. Resistant organisms are more prevalent in children younger than 2 years of age and in those who have recurrent or persistent AOM. Overdiagnosing AOM, selecting inappropriate empiric therapy, or both, leads to overuse and misuse of antibiotics and causes increased drug resistance. This article reviews persistent and recurrent AOM and discusses the pitfalls of diagnosis and the practical limitations of current treatment recommendations.

Increased clinical failures when treating acute otitis media with macrolides: a meta-analysis

BACKGROUND

Macrolide antibiotics are often used to treat children with acute otitis media (AOM); however, the 2004 American Academy of Pediatrics (AAP) and American Academy of Family Physicians guidelines recommend against their use in patients without history of a type I allergic reaction to penicillins.

OBJECTIVE

To evaluate via meta-analysis the comparative efficacy of amoxicillin or amoxicillin/clavulanate to that of macrolide antibiotics in the treatment of children with AOM.

METHODS

A systematic literature search of MEDLINE, EMBASE, and International Pharmaceutical Abstracts was conducted from the earliest available date through September 2008. We used the following MeSH and key words: amoxicillin, amoxicillin/clavulanate, Augmentin, azithromycin, ceftriaxone, clarithromycin, macrolides, AND media, otitis media, and effusion. Included studies were randomized, blinded, and controlled trials evaluating guideline-recommended antibiotics (amoxicillin or amoxicillin/clavulanate) compared to macrolide antibiotics (azithromycin or clarithromycin) in AOM in children. The primary outcome assessed was clinical failure measured between days 10 and 16 after starting antibiotic therapy. Results are reported as relative risks (RRs) with 95% confidence intervals and were calculated using a random-effects model.

RESULTS

A total of 10 trials (N = 2766) evaluating children 6 months-15 years old were included in the meta-analysis. Upon meta-analysis, the use of macrolide antibiotics was associated with an increased risk of clinical failure (RR 1.31 [95% CI 1.07 to 1.60]; p = 0.008) corresponding to a number needed to harm of 32. Upon safety analysis, rates of any adverse reaction (RR 0.74 [95% CI 0.60 to 0.90]; p = 0.003) and diarrhea (RR 0.41 [95% CI 0.32 to 0.52]; p < 0.0001) were significantly lower in the macrolide group.

CONCLUSIONS

The meta-analysis suggests that patients treated with macrolides for AOM may be more likely to have clinical failures. As such, it supports the current AAP AOM recommendation that macrolides be reserved for patients who can not receive amoxicillin or amoxicillin/clavulanate.

Variations in amoxicillin pharmacokinetic/pharmacodynamic parameters may explain treatment failures in acute otitis media

Pharmacokinetic/pharmacodynamic (PK/PD) modeling and Monte Carlo simulations suggest that amoxicillin should rarely fail as therapy for Streptococcus pneumoniae and Haemophilus influenzae acute otitis media (AOM) infections except when the S. pneumoniae are highly penicillin resistant or the H. influenzae are beta-lactamase producing. However, important and not infrequent exceptions to this expectation have been described. The objective of this review was to define the biologic variations in amoxicillin PK/PD parameters for the treatment of AOM in children and assess whether these variations could explain why the commonly employed amoxicillin PK/PD model is imperfect in predicting outcome for every patient in this clinical setting. To this end, a literature search of MEDLINE (1966-2006) and EMBASE (1974-2006) was conducted to identify studies that evaluated ampicillin or amoxicillin intestinal absorption, serum concentrations, and/or middle ear fluid (MEF) concentrations. Analysis of studies identified for review showed that the intestinal bioavailability of amoxicillin depends on passive diffusion and a saturable 'pump' mechanism that produces variable serum concentrations of the antibacterial agent. Indeed, substantial differences from patient to patient in serum (5- to 30-fold) and MEF (up to 20-fold) concentrations of amoxicillin occur following oral administration, and 15-35% of children have no detectable amoxicillin in MEF. These findings suggest that variability in PK/PD parameters may impact amoxicillin concentrations in serum and MEF, possibly explaining some AOM treatment failures.

Comparison of standard versus double dose of amoxicillin in the treatment of non-severe pneumonia in children aged 2-59 months: a multi-centre, double blind, randomised controlled trial in Pakistan

INTRODUCTION

WHO pneumonia case management guidelines recommend oral amoxicillin as first line treatment for non-severe pneumonia. Increasing treatment failure rates have been reported over a period of time, which could possibly be due to increasing minimum inhibitory concentrations of Streptococcus pneumoniae and Haemophilus influenzae for amoxicillin. Microbiological data show that this resistance can be overcome by increasing amoxicillin dosage. Based on this data, we examined whether we can improve the clinical outcome in non-severe pneumonia by doubling the dose of amoxicillin.

METHODS

A double blind randomised controlled trial was conducted in the outpatient departments of four large hospitals in Pakistan. Children aged 2-59 months with non-severe pneumonia were randomised to receive either standard (45 mg/kg/day) or double dose (90 mg/kg/day) oral amoxicillin for 3 days and then followed up for 14 days. Final outcome was treatment failure by day 5.

RESULTS

From September 2003 to June 2004, 876 children completed the study. 437 were randomised to standard and 439 to double dose oral amoxicillin. 20 (4.5%) children in the standard and 25 (5.7%) in the double dose group had therapy failure by day 5. Including the relapses, by day 14 there were 26 (5.9%) cumulative therapy failures with standard and 35 (7.9%) with double dose amoxicillin. These differences were not statistically significant (p = 0.55 and p = 0.29, respectively).

CONCLUSION

Clinical outcome in children aged 2-59 months with non-severe pneumonia is the same with standard and double dose oral amoxicillin. Non-severe pneumonia can be treated effectively and safely with a 3 day course of a standard dose.

Empiric first-line antibiotic treatment of acute otitis in the era of the heptavalent pneumococcal conjugate vaccine

OBJECTIVES

Our goal was to estimate the local prevalence of Streptococcus pneumoniae nonsusceptible to penicillin and amoxicillin after widespread use of the heptavalent pneumococcal vaccine and to revise community-specific recommendations for first-line antibiotic treatment of acute otitis media.

METHODS

We conducted serial prevalence surveys between 2000 and 2004 in the offices of community pediatricians in St Louis, Missouri. Study participants were children <7 years of age with acute upper respiratory infections. Children treated with an antibiotic in the past 4 weeks were excluded. S pneumoniae was isolated from nasopharyngeal swabs using standard techniques. Isolates with a penicillin minimum inhibitory concentration >2 microg/mL were considered to be S pneumoniae nonsusceptible to amoxicillin.

RESULTS

There were 327 patients enrolled in the study. Between 2000 and 2004, vaccine coverage with > or =3 doses of heptavalent pneumococcal vaccine increased from 0% to 54%, but nasopharyngeal carriage of S pneumoniae was stable at 39%. The prevalence of S pneumoniae nonsusceptible to penicillin fell from 25% to 12% among patients, did not vary if <2 years of age, was reduced in children with > or =3 doses of heptavalent pneumococcal vaccine, and increased in child care attendees but reduced in attendees who had > or =3 doses of heptavalent pneumococcal vaccine. The prevalence of S pneumoniae nonsusceptible to amoxicillin in patients remained <5%.

CONCLUSIONS

In our community, widespread use of heptavalent pneumococcal vaccine has reduced the prevalence of S pneumoniae nonsusceptible to penicillin, and the prevalence of S pneumoniae nonsusceptible to amoxicillin remains low (<5%). If antibiotic treatment is elected for children with uncomplicated acute otitis media, we recommend treatment with standard-dose amoxicillin (40-45 mg/kg per day) for children with > or =3 doses of heptavalent pneumococcal vaccine, regardless of age and child care status. High-dose amoxicillin should be used for children with <3 doses of heptavalent pneumococcal vaccine and those treated recently with an antibiotic.

The role of pharmacodynamic research in the assessment and development of new antibacterial drugs

Antibacterial resistance continues to increase world wide, with some bacterial pathogens exhibiting resistance to virtually all available drugs. As the plague of antibacterial resistance continues to grow and create serious therapeutic problems, it is essential that the development of new antibacterial agents continue. Pharmacodynamic research plays an important role in the development of new antibacterial agents, as pharmacodynamic data can help define the clinical potential of a new drug and identify the strengths and weaknesses in comparison to other drugs already on the market. Furthermore, pharmacodynamic experiments can help focus the clinical phases of drug development by providing key information on the pharmacodynamic parameters that influence efficacy and the pharmacodynamic targets that should be achieved to optimize clinical success. Characterization of these pharmacodynamic properties for a new drug in development can help direct the design of the best dose and dosing strategy for clinical trials. This review will focus on the tools, methods, and strategies used to characterize the pharmacodynamics of antibacterial agents and aide in their development for clinical use.

New formulations of amoxicillin/clavulanic acid: a pharmacokinetic and pharmacodynamic review

The pharmacokinetic properties of amoxicillin and clavulanic acid when used alone or in combination are extensively reviewed and discussed in this article. The reported data support a nonlinear absorption process for amoxicillin. Saturable transport mechanisms, limited solubility and the existence of an absorption window are possibly involved in the gastrointestinal absorption of this antibacterial, all leading to a decrease in the peak plasma concentration (Cmax)/dose ratio, a prolongation of the time to reach Cmax, and broad variability for high doses of amoxicillin. Data available in the literature also suggest a possible interaction between amoxicillin and clavulanic acid that might decrease the absolute bioavailability of clavulanic acid. In the present review the intrinsic pharmacodynamics of each drug, together with the synergism produced by the amoxicillin/clavulanic acid association, are also reviewed and analysed. Not only beta-lactamase-producing strains, but also Streptococcus pneumoniae strains, seem to be more efficiently eradicated by the association of amoxicillin and clavulanic acid, and a relevant post-antibacterial effect and post-beta-lactamase inhibitor effect are likely to operate when amoxicillin is administered together with clavulanic acid. The principles of pharmacokinetic/pharmacodynamic analysis applied to amoxicillin are reviewed, with special emphasis being placed on the results obtained from in vitro studies and animal models regarding the new pharmacokinetically enhanced formulation. Theoretical considerations concerning the efficacy of this formulation provided by the application of pharmacokinetic/pharmacodynamic analysis to the scarce pharmacokinetic data available are also included. The broad pharmacokinetic variability of both amoxicillin and clavulanic acid, particularly when administered together and at high doses of amoxicillin, is highlighted and the interest in considering this aspect to improve predictions based on pharmacokinetic/pharmacodynamic analyses for the new formulations is indicated. Methodological recommendations such as the Monte Carlo simulation are proposed in order to obtain more realistic predictions in clinical practice.

Beta-lactam antibiotics: newer formulations and newer agents

beta-Lactam antibiotics share a common structure and mechanism of action, although they differ in their spectrum of antimicrobial activity and utility in treating different infections. The current classes include the penicillins, the penicillinase-resistant penicillins, the extended- spectrum penicillins, the cephalosporins, the carbapenems, and the monobactams. This article discusses some of the newest beta-lactams available for use in the United States: ertapenem, cefditoren, and cefepime. A new formulation of amoxicillin-clavulanate, which contains higher doses of amoxicillin, is also discussed.

Changes in frequency and pathogens causing acute otitis media in 1995-2003

OBJECTIVE

This study was undertaken to determine whether a change in the frequency or distribution of the causative pathogens in persistent acute otitis media (AOM) and AOM treatment failure (AOMTF) occurred after publication of the Centers for Disease Control and Prevention AOM treatment guidelines advocating high dose amoxicillin in 1998 and the universal use of the pneumococcal conjugate vaccine in 2000.

METHODS

This was a 9-year prospective study in a suburban, community-based private practice. To identify bacterial isolate(s), 551 children with AOM who had not responded after 1 or 2 empiric antimicrobial treatment courses (termed persistent AOM) and those who were failures after 48 h on treatment (AOMTF) underwent tympanocentesis. Three periods were compared: (1) 1995-1997 when all enrolled received standard dose amoxicillin (40-50 mg/kg/day divided 3 times daily) as the initial empiric treatment; (2) 1998-2000 when all received high dose amoxicillin (80-100 mg/kg/day divided twice daily); and (3) 2001-2003 when high dose amoxicillin and pneumococcal conjugate vaccinations were used.

RESULTS

Persistent AOM or AOMTF for which tympanocentesis was performed occurred in 195 (16.2%) of 1,207, 204 (16.1%) of 1,278 and 152 (12.3%) of 1,232 AOM visits for 1995-1997, 1998-2000 and 2001-2003, respectively; the 24% decline in 2001-2003 in persistent AOM and AOMTF was significant (P = 0.007). Middle ear aspirates grew Streptococcus pneumoniae (48, 44 and 31%) and Haemophilus influenzae (38, 43 and 57%) for time periods 1, 2 and 3, respectively. There was a significant decline in S. pneumoniae (P = 0.017) and increase in H. influenzae (P = 0.012) isolations and of H. influenzae that were beta-lactamase-producing (P = 0.04) among middle ear fluid isolates. Also there was a trend for an increased proportion of S. pneumoniae in 2001-2003 that were penicillin-susceptible (P = 0.17).

CONCLUSIONS

In our experience, persistent AOM and AOMTF has decreased in frequency since the introduction of high dose amoxicillin therapy and pneumococcal conjugate vaccination. It appears that H. influenzae has become the predominant pathogen of persistent AOM and AOMTF since universal immunization with the pneumococcal conjugate vaccine. Fewer S. pneumoniae AOM isolates are penicillin-resistant and more H. influenzae are beta-lactamase-producing.

Developing community-specific recommendations for first-line treatment of acute otitis media: is high-dose amoxicillin necessary?

OBJECTIVES

National recommendations are to use high-dose amoxicillin (80-90 mg/kg per day) to treat uncomplicated acute otitis media (AOM) in children who are at high risk for infection with nonsusceptible Streptococcus pneumoniae (NSSP). However, high-dose treatment may not be necessary if the local prevalence of NSSP is low. The objective of this study was to estimate the local prevalence of NSSP in children with acute upper respiratory illnesses and to develop community-specific recommendations for first-line empiric treatment of AOM.

METHODS

We conducted a cross-sectional prevalence study in the offices of 7 community pediatricians in St Louis, Missouri. S pneumoniae was isolated from nasopharyngeal swabs collected from children who were younger than 7 years and had AOM, nonspecific upper respiratory infection, cough, acute sinusitis, or pharyngitis. Children were excluded from the study when they had received an antibiotic in the previous 4-week period. Parents and providers completed a brief questionnaire to assess risk factors for carriage of NSSP. On the basis of National Clinical Chemistry Laboratory Standards, isolates with a penicillin minimum inhibitory concentration > or =0.12 microg/mL were considered to be nonsusceptible to penicillin (NSSP), and isolates with a penicillin minimum inhibitory concentration >2 microg/mL were categorized as nonsusceptible to standard-dose amoxicillin (35-45 mg/kg per day; NSSP-A).

RESULTS

S pneumoniae was isolated from the nasopharynx of 85 (40%) of 212 study patients (95% confidence interval [CI]: 33%-47%); 41 (48%) of 85 isolates were NSSP (95% CI: 37%-59%), and 6 (7%) were NSSP-A (95% CI: 1.5%-13%). Among the 212 study patients, the prevalence of NSSP was 19% (95% CI: 14%-25%), and the prevalence of NSSP-A was 3% (95% CI: 0.6%-5%). Carriage of NSSP was increased in child care attendees compared with nonattendees (29% vs 14%; odds ratio: 2.6; 95% CI: 1.3-5.2).

CONCLUSIONS

In our community, although the prevalence of NSSP among isolates of S pneumoniae identified from the nasopharynx of symptomatic children is high (48%), the probability of NSSP-A infection among symptomatic children is <5%. Our data support a recommendation to treat most children who have uncomplicated AOM with standard-dose amoxicillin. Children who attend child care or have recently received an antibiotic may require treatment with high-dose amoxicillin. Other communities may benefit from a similar assessment of the prevalence of NSSP and NSSP-A.

Application of pharmacokinetics and pharmacodynamics to antimicrobial therapy of respiratory tract infections

The pharmacologic field that studies antimicrobial pharmacokinetics and pharmacodynamics (PK/PD) has had a major impact on the choice and dosing regimens used for many antibiotics especially those used in the treatment of respiratory tract infections. PK/PD parameters are particularly important in light of increasing antimicrobial resistance. Drug pharmacokinetic features, such as serum concentrations over time and area under the concentration-time curve, when integrated with minimum inhibitory concentration (MIC) values of antibiotics against pathogens, can predict the probability of bacterial eradication and clinical success. These pharmacokinetic and pharmacodynamic relationships also are important in preventing the selection and spread of resistant strains and have led to the description of the mutation prevention concentration, which is the lowest concentration of antimicrobial that prevents selection of resistant bacteria from high bacterial inocula. b-lactams are time-dependent agents without significant post-antibiotic effects, resulting in bacterial eradication when unbound serum concentrations exceed MICs of these agents against infecting pathogens for >40% to 50% of the dosing interval. Macrolides, azaolides, and lincosamides are time-dependent agents with prolonged post-antibiotic effects, and fluoroquinolones are concentration-dependent agents, resulting in both cases in bacterial eradication when unbound serum area-under-the-curve to MIC ratios exceed 25 to 30. These observations have led to changes in recommended antimicrobial dosing against respiratory pathogens and are used to assess the role of current agents, develop new formulations, and assess potency of new antimicrobials.

High-Dose Versus Standard-Dose Amoxicillin for Acute Otitis Media

BACKGROUND:

Emergence of drug-resistant bacteria has led to a recommendation to use high-dose (HD) amoxicillin (80–90 mg/kg/d) rather than standard-dose (SD) amoxicillin (40–45 mg/kg/d) to treat children with acute otitis media (AOM).

OBJECTIVE:

To compare the efficacy and tolerability of HD versus SD amoxicillin among children with AOM who were considered at low risk for infection with antibiotic-resistant bacteria.

METHODS:

A double-blind, randomized, 3-year clinical trial was conducted using participants who met the following criteria: age >3 mo, weight ≤18 kg, diagnosed with AOM, and candidates for treatment with amoxicillin. The primary endpoint was treatment success at a 3- to 4-day follow-up visit based on the clinical decision to continue the prescribed antibiotic therapy for AOM. Other endpoints included duration of illness, number of office visits and telephone calls related to illness, total number of subsequent AOM episodes, and number of adverse effects.

RESULTS:

The absolute difference in antibiotic failure rate with SD versus HD amoxicillin at the follow-up visit was nonsignificant (95% CI–1.5% to 3.4%; p = 0.78). The mean duration of illness was similar for both doses of amoxicillin (3 ± 2 d). The number of office visits and telephone calls related to illness and the number of subsequent AOM episodes did not differ between the 2 treatment groups. HD amoxicillin did not result in a greater incidence of adverse effects than SD amoxicillin.

CONCLUSIONS:

HD amoxicillin had neither benefit nor detriment compared with SD for AOM in children at low risk for infection with antibiotic-resistant bacteria.

Bacteriologic and clinical efficacy of high dose amoxicillin for therapy of acute otitis media in children

BACKGROUND

High dose (70 to 90 mg/kg/day) amoxicillin is recommended as first line therapy of acute otitis media (AOM) in geographic areas where drug-resistant Streptococcus pneumoniae is prevalent. Information on the bacteriologic efficacy of high dose amoxicillin treatment for AOM is limited.

OBJECTIVES

To evaluate the bacteriologic and clinical efficacy of high dose amoxicillin as first line therapy in AOM.

METHODS

In a prospective study 50 culture-positive patients ages 3 to 22 months (median, 9 months; 77% <1 year) were treated with high dose amoxicillin (80 mg/kg/day three times a day for 10 days) No antibiotics were administered 72 h before enrollment. Twenty-four (48%) patients presented with their first episode of AOM. Middle ear fluid was cultured by tympanocentesis at enrollment and on Days 4 to 6 of therapy. Additional middle ear fluid cultures were obtained if clinical relapse occurred. Bacteriologic failure was defined by positive cultures on Days 4 to 6 and clinical failure by no change or worsening of AOM signs and symptoms and requirement for additional antibiotics during therapy and/or at end of therapy. Patients were followed until Day 28 +/- 2. Susceptibility to penicillin and amoxicillin was measured by E-test.

RESULTS

Sixty-five organisms were recovered at enrollment: Haemophilus influenzae (38), Streptococcus pneumoniae (24), Streptococcus pyogenes (2) and Moraxella catarrhalis (1). Eighteen (75%) S. pneumoniae were nonsusceptible to penicillin (MIC > 0.1 microg/ml). All 24 S. pneumoniae isolates had amoxicillin MIC < or = 2.0 microg/ml. Thirteen (34%) of the 38 H. influenzae were beta-lactamase producers. Eradication was achieved in 41 (82%) patients for 54 of 65 (83%) pathogens: 22 of 24 (92%) S. pneumoniae, 21 of 25 (84%) beta-lactamase-negative H. influenzae, 8 of 13 (62%) beta-lactamase-positive H. influenzae, 2 of 2 S. pyogenes and 1 of 1 M. catarrhalis. Seven organisms not initially present were isolated on Days 4 to 6 in 5 patients: 3 beta-lactamase-positive H. influenzae; 1 beta-lactamase-negative H. influenzae; 2 S. pneumoniae; and 1 M. catarrhalis. In total 14 of 50 (28%) patients failed bacteriologically on Days 4 to 6 (persistence + new infection), of whom 9 (64%) had beta-lactamase-positive H. influenzae. Three (33%) of the 9 patients with bacteriologic failure (2 beta-lactamase-positive H. influenzae, 1 S. pneumoniae) failed also clinically on Days 4 to 6.

CONCLUSIONS

The predominant pathogens isolated from children with AOM failing high dose amoxicillin therapy were beta-lactamase-producing organisms. Because its overall clinical efficacy is good, high dose amoxicillin is still an appropriate choice as first line empiric therapy for AOM, followed by a beta-lactamase-stable drug in the event of failure.

Appropriate use of antibiotics for common infections in an era of increasing resistance

In many respects, antibiotics have changed medicine forever. Countless lives have been enhanced and saved with antibiotic use. Unfortunately, the medical community has opened Pandora's box through the casual distribution of outpatient antibiotics. Society will indeed suffer, as well as the medical profession, if antibiotics are not used judiciously. To date, the rate of penicillin resistance has steadily risen in North America and in many other areas of the world. Much of the increase in resistance has been caused by the distribution of antibiotics for viral infections (e.g., bronchitis, colds, or purulent nasal discharge) as well as nonstreptococcal throat infections. Parental pressure for physicians to prescribe antibiotics also has contributed to the rise in antibiotic resistance. The authors have discussed many common pediatric ED infections and have illustrated the key points for making the diagnosis of each. In addition, the authors also recommend the appropriate choice of antibiotics for each disease process, with an emphasis on narrow-spectrum, first-line antimicrobials. Physicians, as the "holders of the prescription pad," should be aware of the problems with increasing bacterial resistance especially ED practitioners who work on the front line. In addition, families and patients should be educated about the harm of inappropriate antibiotic use. The AAP publishes pamphlets for parents that discuss these issues. It is believed, as was seen in Finland and Japan, that judicious use of antibiotics leads to a decrease in resistant bacteria and prolong antibiotic usefulness. This is an issue of great importance to the long-term health of patients. What Benjamin Rush stated in 1789 is true today: "Do not condemn, or oppose, unnecessarily, the simple, prescriptions of your patients. Yield to them in matters of little consequence but maintain an inflexible authority over matters that are essential to life."

Microbiology of acute otitis media recently treated with aminopenicillins

INTRODUCTION

Sparse recent data are available in the United States regarding the pathogens of acute otitis media (AOM) most likely to be recovered from children recently treated with the two most frequently prescribed antibiotics, amoxicillin or amoxicillin/clavulanate (AMC).

METHODS

Of the 704 rural Kentucky children with culture-positive AOM who underwent a single tympanocentesis or culture of otorrhea between 1992 and 1998, 96 pathogens were recovered from 90 children during therapy or within 7 days posttherapy with an aminopenicillin. Identification and susceptibility testing of AOM pathogens were performed by routine National Committee for Clinical Laboratory Standards methods.

RESULTS

Pathogens recovered from children with AOM recently treated (0 to 7 days) with amoxicillin (n = 38) and AMC (n = 58), respectively, were as follows: Haemophilus influenzae (beta-lactamase-negative), 16 and 29%; H. influenzae (beta-lactamase-positive), 11 and 22%; penicillin-susceptible Streptococcus pneumoniae, 26 and 12%; intermediately penicillin-nonsusceptible S. pneumoniae (PNSP), 20 and 10%; resistant PNSP 13 and 17%; Moraxella catarrhalis (beta-lactamase-positive), 13 and 7%; and Streptococcus pyogenes, 3 and 2%. H. influenzae was also isolated from 8 (75%) of 12 children treated with high dose AMC ( approximately 80 mg/kg/day amoxicillin component). Significantly fewer children recently treated with amoxicillin were otitis-prone than those given AMC (24% vs. 74%, P < 0.0001).

CONCLUSIONS

The predominant pathogen recovered from children with AOM recently treated with amoxicillin was S. pneumoniae (59%) rather than beta-lactamase-producing organisms (24%). H. influenzae was the predominant (51%) pathogen, rather than PNSP (27%), recovered from children recently treated with AMC.

Pharmacokinetic and pharmacodynamic parameters for antimicrobial effects of cefotaxime and amoxicillin in an in vitro kinetic model

An in vitro kinetic model was used to study the relation between pharmacokinetic and pharmacodynamic (PK-PD) parameters for antimicrobial effect, e.g., the time above MIC (T>MIC), maximum concentration in serum (C(max)), and area under the concentration-time curve (AUC). Streptococcus pyogenes and Escherichia coli were exposed to cefotaxime, and the activity of amoxicillin against four strains of Streptococcus pneumoniae with different susceptibilities to penicillin was studied. The drug elimination rate varied so that the T>MIC ranged from 20 to 100% during 24 h, while the AUC and/or the initial concentration (C(max)) were kept constant. For S. pyogenes and E. coli, the maximal antimicrobial effect (E(max)) at 24 h occurred when the antimicrobial concentration exceeded the MIC for 50 and 80% of the strains tested, respectively. The penicillin-susceptible pneumococci (MIC, 0.03 mg/liter) and the penicillin-intermediate strain (MIC, 0.25 mg/liter) showed maximal killing by amoxicillin at a T>MIC of 50%. For a strain for which the MIC was 2 mg/liter, C(max) needed to be increased to achieve the E(max). Under the condition that C(max) was 10 times the MIC, E(max) was obtained at a T>MIC of 60%, indicating that C(max), in addition to T>MIC, may be an important parameter for antimicrobial effect on moderately penicillin-resistant pneumococci. For the strain for which the MIC was 4 mg/liter, the reduction of bacteria varied from -0.4 to -3.6 log(10) CFU/ml at a T>MIC of 100%, despite an initial antimicrobial concentration of 10 times the MIC. Our studies have shown that the in vitro kinetic model is a useful complement to animal models for studying the PK-PD relationship for antimicrobial effect of antibiotics.

Measuring and interpreting associations between antibiotic use and penicillin resistance in Streptococcus pneumoniae

Studies of the relationship between antibiotic use and resistance in pneumococci have produced conflicting results, reflecting differences in study design, setting, and measures of association used. Mathematical models of pneumococcal transmission dynamics provide a framework for interpreting and reconciling these studies. The model predicts, and the review of published studies confirms, that treatment often has little effect in increasing an individual's absolute risk of carrying/being infected by penicillin-resistant Streptococcus pneumoniae (PRSP). However, treatment substantially increases a patient's risk of carriage of/infection by PRSP relative to that of penicillin-susceptible S. pneumoniae (PSSP). The appropriate measure of association depends on the question of interest. Antibiotic use can substantially increase the prevalence of risk in the community as a whole, even when there is a small or nonexistent effect of treatment on the absolute risk that a treated individual will carry a resistant organism. Recommendations for the design and analysis of future studies of antibiotic treatment and pneumococcal resistance are proposed.

treatment and prevention of otitis media

OBJECTIVE

To review and summarize recent advances in the treatment and prevention of otitis media (OM).

DATA SOURCES

A MEDLINE search (1996-March 2000) was performed to identify relevant primary and review articles. References from these articles were also reviewed if deemed important.

STUDY SELECTION AND DATA EXTRACTION

English-language primary and review articles focusing on the treatment and prevention of acute otitis media (AOM) were included. Studies focusing exclusively on OM with effusion or serous OM and chronic suppurative OM were excluded. Information regarding prevention and drug therapy was reviewed, with an emphasis placed on advances made in the last two years.

DATA SYNTHESIS

Recently, an expert panel of the Centers for Disease Control and Prevention recommended use of only three of 16 systemic antibiotics approved by the Food and Drug Administration for treatment of AOM: amoxicillin, cefuroxime axetil, and ceftriaxone. Controversy exists over the importance of key selection factors used by the expert panel in determining which antibiotics to recommend in a two-step treatment algorithm, that is, in vitro data, pharmacodynamic profiles, and necessity for coverage of drug-resistant Streptococcus pneumoniae at all steps of empiric treatment. Additional antibiotic and patient selection factors useful for individualizing therapy include clinical efficacy, adverse effects, frequency and duration of administration, taste, cost, comorbid infections, and ramifications should bacterial resistance develop to the chosen antibiotic. Presumed or past patient/caregiver adherence (especially when antibiotic failure has occurred) is also paramount in selecting antibiotic therapy. A three-step treatment algorithm for refractory AOM that employs amoxicillin, trimethoprim/sulfamethoxazole (TMP/SMX), or high-dose amoxicillin/clavulanate (depending on the prior dose of and adherence to amoxicillin therapy), and ceftriaxone or tympanocentesis at steps 1, 2, and 3, respectively, appears rational and cost-effective. The recent upsurge in antimicrobial resistance is highlighted, and recommendations are presented for the treatment of AOM and prevention of recurrent otitis media (rAOM).

CONCLUSIONS

Amoxicillin remains the antibiotic of choice for initial empiric treatment of AOM, although the traditional dosage should be increased in patients at risk for drug-resistant S. pneumoniae. In cases refractory to high-dose amoxicillin, TMP/SMX should be prescribed if adherence to prior therapy seemed good or complete, or high-dose amoxicillin/clavulanate if adherence was incomplete or questionable. Ceftriaxone should be reserved as third-line treatment. The increasing prevalence of drug-resistant S. pneumoniae emphasizes the importance of alternative medical approaches for the prevention of OM, as well as judicious antibiotic use in established cases. Removal of modifiable risk factors should be first-line therapy for prevention of rAOM. We support the use of conjugate pneumococcal vaccine per guidelines for prevention of rAOM from the Advisory Committee on Immunization Practice of the Centers for Disease Control and Prevention, with consideration given to influenza vaccine for cases of rAOM that historically worsen during the flu season. Sulfisoxazole prophylaxis should be reserved for children who are immunocompromised, have concurrent disease states exacerbated by AOM, or meet the criteria of rAOM despite conjugate pneumococcal and influenza vaccination. Therapy should be intermittent, beginning at the first sign of an upper respiratory infection, and should continue for 10 days. The invasive nature and risks of anesthesia relegate myringotomy, tympanostomy tubes, and adenoidectomy to last-line therapies for rAOM.

Drug-resistant Streptococcus pneumoniae: rational antibiotic choices

Increasingly, Streptococcus pneumoniae with reduced susceptibility to penicillin is becoming a healthcare concern, not only because of the high prevalence of infections caused by this pathogen but also because of the rate at which resistance has progressed. The incidence of penicillin resistance in strains of S. pneumoniae approaches 40% in some areas of the United States, and the incidence of high-level resistance has increased by 60-fold during the past 10 years. With the exception of meningitis and otitis media, there is no conclusive evidence that the acquisition of resistance by S. pneumoniae to beta-lactam antibiotics incurs greater morbidity and mortality in infections caused by this pathogen. However, if the current trends of resistance patterns continue, one can expect the morbidity and mortality to increase. The mechanism of beta-lactam resistance of S. pneumoniae involves genetic mutations which alter penicillin-binding protein structure, resulting in a decreased affinity for all beta-lactam antibiotics. In the treatment of infections caused by S. pneumoniae, it should not be assumed that nonsusceptibility to beta-lactam antibiotics correlates with clinical ineffectiveness of these agents. On the contrary, the recommended therapy for nonmeningeal pneumococcal infections (e.g., pneumonia, sepsis, acute otitis media) includes a beta-lactam antibiotic: penicillin G, amoxicillin, amoxicillin/clavulanate, cefuroxime, cefotaxime, or ceftriaxone. Recommended therapy for meningitis is cefotaxime or ceftriaxone, with the addition of vancomycin until susceptibility is known. These agents are recommended because of their ability to achieve serum/tissue concentrations greater than the minimum inhibitory concentrations (MICs) of these agents against penicillin-susceptible, penicillin-intermediate, and most penicillin-resistant strains (e.g., penicillin G, cefotaxime, ceftriaxone, amoxicillin, amoxicillin/clavulanate, and cefuroxime), or their ability to provide adequate concentrations in cerebrospinal fluid (e.g., cefotaxime, ceftriaxone).

Pharmacodynamics of trovafloxacin, ofloxacin, and ciprofloxacin against Streptococcus pneumoniae in an in vitro pharmacokinetic model

An in vitro pharmacokinetic model was used to simulate the pharmacokinetics of trovafloxacin, ofloxacin, and ciprofloxacin in human serum and to compare their pharmacodynamics against eight Streptococcus pneumoniae strains. The MICs of ofloxacin and ciprofloxacin ranged from 1 to 2 micrograms/ml. Trovafloxacin was 8- to 32-fold more potent, with MICs of 0.06 to 0.12 microgram/ml. Logarithmic-phase cultures were exposed to peak concentrations of trovafloxacin, ofloxacin, or ciprofloxacin achieved in human serum after 200-, 400-, and 750-mg oral doses, respectively. Trovafloxacin was dosed at 0 and 24 h, and ofloxacin and ciprofloxacin were dosed at 0, 12, and 24 h. Human elimination pharmacokinetics were simulated, and viable bacterial counts were measured at 0, 2, 4, 6, 8, 12, 24, and 36 h. Trovafloxacin was rapidly and significantly bactericidal against all eight strains evaluated, with viable bacterial counts decreasing at least 5 logs to undetectable levels. Times to 99.9% killing were only 1 to 3 h. Although the rate of killing with ofloxacin was substantially slower than that with trovafloxacin, ofloxacin was also able to eradicate all eight strains from the model, despite a simulated area under the inhibitory curve/MIC ratio (AUC/MIC) of only 49. In contrast, ciprofloxacin eradicated only five strains (AUC/MIC = 44) from the model. Against the other three strains (AUC/MIC = 22), the antibacterial activity of ciprofloxacin was substantially diminished. These data corroborate clinical data and suggest that trovafloxacin has a pharmacodynamic advantage over ciprofloxacin and ofloxacin against S. pneumoniae in relation to its enhanced antipneumococcal activity.

Management of acute otitis media in the 1990s: the decade of resistant pneumococcus

Acute otitis media (AOM) has become increasingly difficult to treat in the 1990s, the decade of drug-resistant pneumococcus. Throughout the world, drug-resistant strains of this pathogen are being recovered from 20 to 50% of cases of initial untreated AOM, and from 45 to 90% of refractory AOM. Almost as alarming is that beta-lactamase-producing strains of Haemophilus influenzae are currently being isolated in 40 to 50% of cases of AOM in the US. Clinicians can no longer expect 'Pollyanna-like' high rates of clinical resolution for this disease. It is now imperative that they become aware of the regional prevalence of these drug-resistant bacteria and, just as importantly, their patterns of antibacterial resistance. Although some authors would hold that any antibacterial, or even placebo, should be adequate for most cases of AOM, clinical practice appears to suggest otherwise. Amoxicillin, still the first-line therapeutic choice for initial nonrefractory AOM, will often fail. The real dilemma begins when clinicians search for clinical data to select an antibacterial for therapeutic failures--few data are available. Thus, to give optimal treatment to a child who has failed antibacterial therapy--the true actual indication for all second-line antibacterials--they must instead become familiar with the following in vivo and in vitro data: 1. 'In vivo sensitivity data': otherwise known as bacteriological efficacy, in which repeat tympanocentesis is performed in mid-therapy. This reveals the bacterial 'Achilles heel' or weakness for the individual antibacterial agents. 2. Clinical efficacy data: analysis of rates of clinical resolution after therapy in comparative trials which use a single tympanocentesis initially and a 'gold standard' comparator antibacterial. 3. 'Bug to drug' data: comparison of reported middle ear concentrations for each individual antibacterial agent relative to the respective minimum inhibitory concentrations of isolates, particularly drug-resistant pneumococcus and H. influenzae (if possible, obtained from the paediatric respiratory tract). The selection of an antibacterial agent for AOM in any particular case should not be merely a random process. It involves awareness of the pathogens most likely to be observed: with co-infections; after failure with a particular antibacterial (the bacterial 'Achilles heel' of the drug); and at different points in time, whether initially or after therapeutic failures (e.g. first-line versus fourth-line failure).

Efficacy of high-dose amoxicillin-clavulanate against experimental respiratory tract infections caused by strains of Streptococcus pneumoniae

The purpose of the present investigation was to determine if the efficacy of amoxicillin-clavulanate against penicillin-resistant Streptococcus pneumoniae could be improved by increasing the pediatric amoxicillin unit dose (90 versus 45 mg/kg of body weight/day) while maintaining the clavulanate unit dose at 6.4 mg/kg/day. A rat pneumonia model was used. In that model approximately 6 log10 CFU of one of four strains of S. pneumoniae (amoxicillin MICs, 2 microg/ml [one strain], 4 microg/ml [two strains], and 8 microg/ml [one strain]) were instilled into the bronchi of rats. Amoxicillin-clavulanate was given by computer-controlled intravenous infusion to approximate the concentrations achieved in the plasma of children following the administration of oral doses of 45/6.4 mg/kg/day or 90/6.4 mg/kg/g/day divided every 12 h or saline as a control for a total of 3 days. Infusions continued for 3 days, and 2 h after the cessation of infusion, bacterial numbers in the lungs were significantly reduced by the 90/6.4-mg/kg/day equivalent dosage for strains for which amoxicillin MICs were 2 or 4 microg/ml. The 45/6.4-mg/kg/day equivalent dosage was fully effective only against the strain for which the amoxicillin MIC was 2 microg/ml and had marginal efficacy against one of the two strains for which amoxicillin MICs were 4 microg/ml. The bacterial load for the strain for which the amoxicillin MIC was 8 microg/ml was not reduced with either dosage. These data demonstrate that regimens which achieved concentrations in plasma above the MIC for at least 34% of a 24-h dosing period resulted in significant reductions in the number of viable bacteria, indicating that the efficacy of amoxicillin-clavulanate can be extended to include efficacy against less susceptible strains of S. pneumoniae by increasing the amoxicillin dose.

Pharmacodynamics of levofloxacin and ciprofloxacin against Streptococcus pneumoniae

An in-vitro pharmacokinetic model was used to compare the pharmacodynamics of levofloxacin and ciprofloxacin against four penicillin-susceptible and four penicillin-resistant Streptococcus pneumoniae. Logarithmic-phase cultures were exposed to the peak concentrations of levofloxacin or ciprofloxacin observed in human serum after 500 mg and 750 mg oral doses, human elimination pharmacokinetics were simulated, and viable bacterial counts were measured at 0, 1, 2, 4, 6, 8, 12, 24 and 36 h. Levofloxacin was rapidly and significantly bactericidal against all eight strains evaluated, with eradication of six strains occurring despite area under the inhibitory curve over 24 h (AUIC24) values of only 32-64 SIT(-1) x h (serum inhibitory titre over time). The pharmacodynamics of ciprofloxacin were more variable and the rate of bacterial killing was consistently slower than observed with levofloxacin. Ciprofloxacin eradicated five strains despite having an AUIC24 of only 44 SIT(-1) x h. These data suggest that the increased potency of levofloxacin and more favourable pharmacokinetics compared with ciprofloxacin provide enhanced pharmacodynamic activity against S. pneumoniae. Furthermore, these data suggest that the minimum AUIC required for clinical efficacy against and eradication of S. pneumoniae with levofloxacin and ciprofloxacin may be well below the 125 SIT(-1) x h identified by other studies.