Macrolide antibiotics in paediatric infectious diseases

The role of adjuvants in overcoming antibacterial resistance due to enzymatic drug modification

Antibacterial resistance is a prominent issue with monotherapy often leading to treatment failure in serious infections. Many mechanisms can lead to antibacterial resistance including deactivation of antibacterial agents by bacterial enzymes. Enzymatic drug modification confers resistance to β-lactams, aminoglycosides, chloramphenicol, macrolides, isoniazid, rifamycins, fosfomycin and lincosamides. Novel enzyme inhibitor adjuvants have been developed in an attempt to overcome resistance to these agents, only a few of which have so far reached the market. This review discusses the different enzymatic processes that lead to deactivation of antibacterial agents and provides an update on the current and potential enzyme inhibitors that may restore bacterial susceptibility.

Genotypic differences in CC224, CC363, CC449 and CC446 of Moraxella catarrhalis isolates based on whole genome SNP, MLST and PFGE typing

Understanding the evolutionary path of M. catarrhalis from macrolide-susceptible to macrolide-resistant organism, is important for hindering macrolide resistance from propagation. Multilocus sequence typing (MLST), pulsed-field gel electrophoresis (PFGE) and whole genome SNP typing (WGST), as useful and practical typing tools, have both advantages and disadvantages. We studied the utility of these 3 typing methods, including the level of agreement, consistency and drawbacks, in characterizing M. catarrhalis clones and clonal complexes. We focused on four clonal complexes [CC224, CC363, CC449 (CCN10) and CC446 (CCN08)] and found that PFGE and WGST had a high level of agreement and a proper consistency of the same clone or very closely related clones, while MLST is less discriminatory for different clones. Furthermore, we also established an evolutionary distance cut-off value for "The same clone". Moreover, we detected macrolide-resistant M. catarrhalis in CC224, which had previously been considered as a macrolide-susceptible clonal complex. A higher number of isolates belonged to ST215 compared to ST446, implying that ST215 is more likely to be the primary founder. Our study also demonstrated that all the four clonal complexes belong to the M. catarrhalis lineage 1, which is considered to be related to increased virulence potential and serum resistance. We also observed that copB II was highly related to CC449 and LOS type B was mainly confined in CC224. In conclusion, these findings provide further insight into the evolutionary characteristics of M. catarrhalis.

Use of next generation sequence to investigate potential novel macrolide resistance mechanisms in a population of Moraxella catarrhalis isolates

Although previous studies have confirmed that 23S rRNA gene mutation could be responsible for most of macrolide resistance in M. catarrhalis, a recent study suggested otherwise. Next generation sequence based comparative genomics has revolutionized the mining of potential novel drug resistant mechanisms. In this study, two pairs of resistant and susceptible M. catarrhalis isolates with different multilocus sequence types, were investigated for potential differential genes or informative single nucleotide polymorphisms (SNPs). The identified genes and SNPs were evaluated in 188 clinical isolates. From initially 12 selected differential genes and 12 informative SNPs, 10 differential genes (mboIA, mcbC, mcbI, mboIB, MCR_1794, MCR_1795, lgt2B/C, dpnI, mcbB, and mcbA) and 6 SNPs (C619T of rumA, T140C of rplF, G643A of MCR_0020, T270G of MCR_1465, C1348A of copB, and G238A of rrmA) were identified as possibly linked to macrolide resistance in M. catarrhalis. Most of the identified differential genes and SNPs are related to methylation of ribosomal RNA (rRNA) or DNA, especially MCR_0020 and rrmA. Further studies are needed to determine the function and/or evolution process, of the identified genes or SNPs, to establish whether some novel or combined mechanisms are truly involved in M. catarrhalis macrolide resistance mechanism.

Azithromycin Extravasation in a Pediatric Patient

Objective:

To report a case of azithromycin infiltration and extravasation in a pediatric patient.

Case Summary:

A 12-month-old African American male, between chemotherapy cycles for acute myelogenous leukemia, self-dislodged his central venous catheter. A peripheral catheter was placed in the right dorsal hand and, 2 days later, azithromycin for injection infiltrated at the infusion site. Several bullae formed in the first web space and a few areas of epidermolysis, each <2 cm wide, later appeared on the forearm. Treatment included warm compresses, adaptee dressing, topical antibiotics, splint placement, and arm elevation. Four months after the incident, there was no visible impairment or restriction to the toddler's use of the right hand or arm. The only residual finding was an area of hypopigmented skin in the dorsal web between the first and second fingers.

Discussion:

As of February 10, 2005, this is the first case published in the English-language literature describing intravenous azithromycin infiltration and extravasation. Infiltration occurs generally by 3 mechanisms. These include the catheter dislodging or causing a hole in the vessel wall, intravenous fluid irritating the vessel wall leading it to rupture or leak, or backflow of intravenous fluid through the catheter insertion site.

Conclusions:

Complications can occur secondary to intravascular therapy, including extravascular extravasation. In this case, infiltration and extravasation injury were probably related to azithromycin. Immediate detection and treatment are critical to decrease morbidity associated with infiltration events.

High-Level Macrolide-Resistant Moraxella catarrhalis and Development of an Allele-Specific PCR Assay for Detection of 23S rRNA Gene A2330T Mutation: A Three-Year Study at a Chinese Tertiary Hospital

Previous studies indicate that macrolide resistance in Moraxella catarrhalis isolates is less common in adults than in children. However, few studies have investigated M. catarrhalis macrolide resistance mechanisms in adult patients. In this study, 124 M. catarrhalis isolates were collected from adult patients in a Chinese tertiary hospital, between 2010 and 2013, and investigated for antimicrobial resistance. We found that only seven isolates were macrolide resistant and all exhibited high-level macrolide resistance (minimum inhibitory concentrations >256 μg/ml). Multilocus sequence typing (MLST) suggested that M. catarrhalis has a diverse population; in particular, both pulsed-field gel electrophoresis and MLST revealed that all the seven high-level macrolide-resistant M. catarrhalis belonged to different clones. A 934-bp 23S rRNA gene sequencing showed that only nine isolates (including all the seven macrolide-resistant isolates) had mutations within the studied region, and only the seven macrolide-resistant isolates had mutation of A2330T. No other known macrolide-resistance determinant genes (ermA, ermB, mefA, or mefE) were detected. These findings support previous studies in children on M. catarrhalis macrolide-resistant isolates and suggest that the 23S rRNA gene A2330T mutation is responsible for the high M. catarrhalis macrolide resistance. The findings prompted us to successfully develop a simple allele-specific polymerase chain reaction assay for high-level macrolide-resistant 23S rRNA gene A2330T mutation for future clinical and further surveillance use.

High prevalence and molecular analysis of macrolide-nonsusceptible Moraxella catarrhalis isolated from nasopharynx of healthy children in China

Three hundred eighty-three isolates of Moraxella catarrhalis were collected from healthy children aged less than 2 years in China and assessed for antimicrobial resistance. We found that 92.2% (n=353) produced a β-lactamase. Nonsusceptibility rates to erythromycin and azithromycin, determined using Clinical Laboratory Standards Institute (CLSI) breakpoints, were 40.3% and 22.5%, respectively; nonsusceptibility rates determined using pharmacokinetics/pharmacodynamics breakpoints, however, were 59% and 60.1%. The minimal inhibitory concentration (MIC)(90) values were >256 μg/ml. Nonsusceptibility rates varied by region from 9.7% in Dongguan to 75.9% in Jinan. Further, concomitant resistance to β-lactam antibiotics was also observed. Pulsed-field gel electrophoresis analysis of 27/37 high-level macrolide-resistant M. catarrhalis isolates showed that closely related pulsotypes dominated, with a total of 11 different pulsotypes being observed. The closely related pulsotypes were observed in isolates originating from all six Chinese cities investigated, possibly as a consequence of the mobility of the Chinese population. Sixteen patterns of 23S rRNA mutations were found among 97 selected isolates using polymerase chain reaction and sequencing, but no known ermA, ermB, mefA, or mefE genes could be detected. Mutations A2982T and A2796T in 23S rRNA were related to high-level macrolide resistance (MICs ranging from 24 to >256 μg/ml), while an A2983T mutation was associated with low-level macrolide resistance (MICs ranging from 0.19 to 16 μg/ml).

Single oral dose of azithromycin versus 5 days of oral erythromycin or no antibiotic in treatment of campylobacter enterocolitis in children: a prospective randomized assessor-blind study

OBJECTIVE

To evaluate efficacy of a single oral azithromycin dose versus standard oral erythromycin regimen or no antibiotic for Campylobacter enterocolitis in children younger than or equal to 12 years of age.

PATIENTS AND METHODS

Randomized parallel group assessor-blind trial testing for inequality in efficacy between treatments was done. Patients (N = 120) were enrolled at less than or equal to 48 hours since disease onset to receive erythromycin 50 mg kg day for 5 days, single-dose azithromycin 20 mg/kg or 30 mg/kg, or no antibiotic (no treatment control) (1: 1: 1: 1). Antibiotics were commenced 8 to 10 hours after enrollment. Patients were assessed at 24-hour intervals for 6 days.

RESULTS

In the intent-to-treat analysis, Campylobacter eradication was achieved in 20 of 30 controls and in all of the patients treated with antibiotic. Incidence of clinical cure during the observed period was 15 of 30 in the control, 14 of 30 in the erythromycin, 20 of 30 in the lower, and 25 of 30 in the higher azithromycin dose group. With adjustment for age, sex, baseline disease severity, and disease duration before enrollment, only azithromycin 30 mg/kg was superior to no treatment: incidence ratio (IR) 1.76 (95% confidence interval [CI] 1.11-2.87). It was also superior to erythromycin (IR 1.80, 97.5% CI 1.13-2.84). Regarding time to clinical cure, only azithromycin 30 mg/kg was superior to no treatment (adjusted hazard ratio [HR] 4.90, 95% CI 2.44-9.84). It was also superior to erythromycin (HR 4.17, 97.5% CI 1.91-9.09). All treatments were well tolerated.

CONCLUSIONS

The administration of single oral dose of azithromycin 30 mg/kg early after disease onset effectively eradicates the pathogen and accelerates clinical cure in childhood Campylobacter enterocolitis. It is clinically superior to an early commenced 5-day erythromycin regimen, which apparently conveys no clinically relevant benefit over no antibiotic treatment.

Clinical and bacteriological outcomes in hospitalised patients with community-acquired pneumonia treated with azithromycin plus ceftriaxone, or ceftriaxone plus clarithromycin or erythromycin: a prospective, randomised, multicentre study

This study compared patients with moderate-to-severe community-acquired pneumonia (CAP) requiring hospitalisation, who received initial therapy with either intravenous ceftriaxone plus intravenous azithromycin, followed by step-down to oral azithromycin (n = 135), with patients who received intravenous ceftriaxone combined with either intravenous clarithromycin or erythromycin, followed by step-down to either oral clarithromycin or erythromycin (n = 143). Clinical and bacteriological outcomes were evaluated at the end of therapy (EOT; day 12-16) or at the end of study (EOS; day 28-35). At baseline, mean APACHE II scores were 13.3 and 12.6, respectively, with >50% of patients classified as Fine Pneumonia Severity Index (PSI) category IV or V. Clinical success rates (cure or improvement) in the modified intent-to-treat (MITT) population at EOT were 84.3% in the ceftriaxone/azithromycin group and 82.7% in the ceftriaxone/clarithromycin or erythromycin group. At EOS, MITT success rates (cure only) were 81.7% and 75.0%, respectively. Equivalent success rates in the clinically evaluable population were 83% and 87%, respectively, at EOT, and 79% and 78%, respectively, at EOS. MITT bacteriological eradication rates were 73.2% and 67.4%, respectively, at EOT, and 68.3% vs. 60.9%, respectively, at EOS. Mean length of hospital stay (LOS) was 10.7 and 12.6 days, and the mean duration of therapy was 9.5 and 10.5 days, respectively. The incidence of infusion-related adverse events was 16.3% and 25.2% (p 0.04), respectively. An intravenous-to-oral regimen of ceftriaxone/azithromycin was at least equivalent in efficacy and safety to the comparator regimen and appeared to be a suitable treatment option for hospitalised patients with CAP.

Neonatal chlamydial infections: prevention and treatment

Neonatal chlamydial infection, which manifests principally as ophthalmia neonatorum (ON) or pneumonia, is a significant cause of neonatal morbidity. Widespread use of silver nitrate drops resulted in a dramatic decline in the incidence of gonococcal ophthalmia but had much less impact on the incidence of neonatal chlamydial infection. Chlamydia trachomatis has become the most common infectious cause of ON in developed countries.A number of prophylactic antibiotic or antiseptic agents have been used to prevent ON. Prophylaxis with 1% silver nitrate ophthalmic drops, 0.5% erythromycin ophthalmic ointment, or 1% tetracycline ointment has comparable efficacy for the prevention of chlamydial ophthalmia but does not offer protection against nasopharyngeal colonization or the development of pneumonia. Erythromycin or tetracycline topically have been used as prophylactic agents because of their allegedly superior activity for the prevention of ON and because they produced less chemical conjunctivitis compared with silver nitrate. However, the relative efficacy of these agents for chlamydial infection and the emergence of beta-lactamase-producing Neisseria gonorrheae has raised questions regarding their effectiveness when applied topically for prophylaxis of ON. Compared with these agents, a 2.5% povidone-iodine ophthalmic solution has been found to have greater efficacy for the prevention of ON generally, and chlamydial ophthalmia specifically. In countries where the incidence of ON is very low, an alternative strategy is to institute prenatal screening and treatment of infected mothers, forgo routine neonatal prophylaxis, and follow-up infants after birth for the possible development of infection. For the treatment of chlamydial ophthalmia or pneumonia, oral erythromycin for 2 weeks is recommended; additional topical therapy is unnecessary. However, in approximately 20-30% of infants, therapy will not eradicate the organism and the infant may require a repeat oral course of antibiotics. The few published studies on the use of the new oral macrolide antibiotics, such as azithromycin, roxithromycin, or clarithromycin for chlamydial infections in neonates suggest that these agents may be effective; however, more data on their tolerability and efficacy in this patient group are warranted.

Macrolide resistance: an increasing concern for treatment failure in children

BACKGROUND

Antimicrobial treatment of pediatric respiratory tract infections has evolved during the past 30 years as a result of antimicrobial resistance. The focus of antimicrobial therapy in these conditions has shifted from penicillins to other agents because of the dramatic increase in antimicrobial resistance among common respiratory pathogens, including Streptococcus pneumoniae, Haemophilus influenzae and Moraxella catarrhalis. It is important for clinicians to understand how resistance develops so that they can help prevent this phenomenon from occurring with other antimicrobials.

METHODS

This article reviews the published literature on resistance to macrolide antimicrobials among common pediatric respiratory tract pathogens and clinical and bacteriologic outcomes of infections with these pathogens.

RESULTS

Resistance among common pediatric respiratory tract pathogens to macrolides occurs through two main mechanisms, alteration of the target site and active efflux. Although resistance patterns vary by geographic region, the widespread use of macrolides has contributed to the emergence of both types of macrolide-resistant organisms. Conditions that favor the selection and proliferation of resistant strains include children with repeated, close contact who frequently receive antimicrobial treatment or prophylaxis, such as children who attend day care. Recent US surveillance data show that 20 to 30% of S. pneumoniae are resistant to macrolides, with approximately two-thirds of macrolide-resistant strains associated with an efflux mechanism and the remainder associated with a ribosomal methylase. Additionally, although less well-known, virtually all strains of H. influenzae have an intrinsic macrolide efflux pump. As resistance to macrolides has increased, clinical failures have resulted, and these agents are no longer considered appropriate for empiric first line antimicrobial therapy of acute otitis media and sinusitis unless patients are truly penicillin-allergic. Therefore, other antimicrobials are recommended for the empiric treatment of children with respiratory tract infections, including higher doses of amoxicillin and amoxicillin/clavulanate (90 mg/kg/day amoxicillin), cefuroxime axetil and intramuscular ceftriaxone.

CONCLUSIONS

As resistance to macrolides increases and clinical failures in children become more common with this class of antimicrobials, judicious use of antimicrobials is needed. This includes limiting antimicrobial use for viral infections and using the most effective agents when antimicrobials are clinically indicated, such as higher doses of amoxicillin and amoxicillin/clavulanate. Application of these principles may prevent proliferation and further development of resistance.

Macrolide-based transgene control in mammalian cells and mice

Heterologous mammalian gene regulation systems for adjustable expression of multiple transgenes are necessary for advanced human gene therapy and tissue engineering, and for sophisticated in vivo gene-function analyses, drug discovery, and biopharmaceutical manufacturing. The antibiotic-dependent interaction between the repressor (E) and operator (ETR) derived from an Escherichia coli erythromycin-resistance regulon was used to design repressible (E(OFF)) and inducible (E(ON)) mammalian gene regulation systems (E.REX) responsive to clinically licensed macrolide antibiotics (erythromycin, clarithromycin, and roxithromycin). The E(OFF) system consists of a chimeric erythromycin-dependent transactivator (ET), constructed by fusing the prokaryotic repressor E to a eukaryotic transactivation domain that binds and activates transcription from ETR-containing synthetic eukaryotic promoters (P(ETR)). Addition of macrolide antibiotic results in repression of transgene expression. The E(ON) system is based on E binding to artificial ETR-derived operators cloned adjacent to constitutive promoters, resulting in repression of transgene expression. In the presence of macrolides, gene expression is induced. Control of transgene expression in primary cells, cell lines, and microencapsulated human cells transplanted into mice was demonstrated using the E.REX (E(OFF) and E(ON)) systems. The macrolide-responsive E.REX technology was functionally compatible with the streptogramin (PIP-regulated and tetracycline (TET-regulated expression systems, and therefore may be combined for multiregulated multigene therapeutic interventions in mammalian cells and tissues.

Role of erythromycin for treatment of incipient chronic lung disease in preterm infants colonised with Ureaplasma urealyticum

Ureaplasma urealyticum is frequently isolated from tracheal aspirates of very low birthweight infants who go on to develop chronic lung disease. The use of erythromycin has been advocated in ventilated very low birthweight infants who are colonised with U. urealyticum, although the association between U. urealyticum and chronic lung disease remains controversial. There are only two randomised, controlled trials involving a total of 37 U. urealyticum-positive very low birthweight infants. Both trials failed to demonstrate a reduction in the incidence of chronic lung disease after 7 or 10 days of erythromycin. On the other hand, there are reports of rare but serious adverse effects of erythromycin in newborn infants including sudden cardiovascular compromise and hypertrophic pyloric stenosis. We conclude that, at present, there is insufficient evidence to support the use of erythromycin for the treatment of incipient chronic lung disease in very low birthweight infants colonised with U. urealyticum.

A new HPLC method for azithromycin quantitation

A simple liquid chromatographic method was developed for the estimation of azithromycin raw material and in pharmaceutical forms. The sample was chromatographed on a reverse phase C18 column and eluants monitored at a wavelength of 215 nm. The method was accurate, precise and sufficiently selective. It is applicable for its quantitation, stability and dissolution tests.

Comparative efficacy of new investigational agents against Helicobacter pylori

BACKGROUND

Emergence of antibiotic resistant Helicobacter pylori has necessitated the identification of alternate therapies for the treatment of this infection.

AIM

To assess the in vitro efficacy of two investigational agents: DMG-MINO CL 344 (a N,N-dimethylglycylamido derivative of minocycline), and davercin, a cyclic carbonate of erythromycin A as compared to older antibiotics (clarithromcyin, azithromycin, minocycline, tetracycline, ofloxacin, ciprofloxacin, cefixime) against clinical isolates of H. pylori.

METHODS

Testing was performed using the agar dilution method approved by the NCCLS subcommittee on antimicrobial susceptibility testing, Helicobacter pylori working group. Under these guidelines, Mueller-Hinton agar containing 5% aged sheep blood was used. All incubations were done under CampyPak Plus conditions for 72 h at 37 degrees C. The drug concentrations in the agar ranged from 0.016 to 16 microg/mL. Twenty-one clarithromycin-resistant and 16 clarithromycin-susceptible clinical isolates of H. pylori obtained from patients with duodenal ulcer were used. H. pylori ATCC 43504 was used as the control in all determinations.

RESULTS

Against clarithromycin susceptible isolates, all antimicrobial agents except the fluoroquinolones were highly effective. Against clarithromycin-resistant H. pylori, the MIC50/MIC90 values showed that the tetracyclines and cefixime were the most efficacious agents. The fluoroquinolones and macrolides were ineffective. Macrolide cross-resistance was detected.

CONCLUSION

Macrolide cross-resistance prevents the use of this entire class of antimicrobials when clarithromycin resistance is present. Tetracyclines and cefixime are possible alternative agents for the treatment of H. pylori infection in these patients.

Use of anti-infective agents during lactation: Part 2--Aminoglycosides, macrolides, quinolones, sulfonamides, trimethoprim, tetracyclines, chloramphenicol, clindamycin, and metronidazole

Because many antibiotics are excreted into breast milk, it can be difficult for a practitioner to choose an antibiotic for a lactating patient that will have minimal risks to her nursing infant. This article is the second of a three-part series discussing the use of anti-infective agents during lactation. The authors review general information regarding use and common side effects for several classes of antibiotics. They also summarize information, including documented milk concentrations, milk-to-plasma ratios, and other pharmacokinetic properties, in a table that can help practitioners choose antibiotics that may be considered safe to use in the lactating mother.

In vitro and in vivo efficacies of T-3811ME (BMS-284756) against Mycoplasma pneumoniae

T-3811, the free base of T-3811ME (BMS-284756), a new des-F(6)-quinolone, showed a potent in vitro activity (MIC at which 90% of the isolates tested are inhibited [MIC(90)], 0.0313 microg/ml) against Mycoplasma pneumoniae. The MIC(90) of T-3811 was 4-fold higher than that of clarithromycin but was 4- to 8-fold lower than those of trovafloxacin, gatifloxacin, gemifloxacin, and moxifloxacin and was 16- to 32-fold lower than those of levofloxacin, ciprofloxacin, and minocycline. In an experimental M. pneumoniae pneumonia model in hamsters, after the administration of T-3811ME (20 mg/kg of body weight as T-3811, once daily, orally) for 5 days, the reduction of viable cells of M. pneumoniae in bronchoalveolar lavage fluid was greater than those of trovafloxacin, levofloxacin, and clarithromycin (20 and 40 mg/kg, orally) (P < 0.05).

Regulation of transcription of the mph(A) gene for macrolide 2'-phosphotransferase I in Escherichia coli: characterization of the regulatory gene mphR(A)

The synthesis of macrolide 2'-phosphotransferase I [Mph(A)], which inactivates erythromycin, is inducible by erythromycin. The expression of high-level resistance to erythromycin requires the mph(A) and mrx genes, which encode Mph(A) and an unidentified protein, respectively. We have studied the mphR(A) gene, which regulates the inducible expression of mph(A). An analysis of the synthesis of Mph(A) in minicells and results of a complementation test indicated that mphR(A) is located downstream from mrx and that its product, MphR(A), represses the production of Mph(A). DNA sequencing indicated that the mph(A), mrx, and mphR(A) genes exist as a cluster that begins with mph(A) and that the deduced amino acid sequence of MphR(A) can adopt an alpha-helix-turn-alpha-helix structure. To study the regulation of gene expression by MphR(A), we performed Northern blotting and primer extension. A transcript of 2. 9 kb that corresponded to the transcript of mph(A) through mphR(A) was detected, and its level was elevated upon exposure of cells to erythromycin. Gel mobility shift assays and DNase I footprinting indicated that MphR(A) binds specifically to the promoter region of mph(A), and the amount of DNA shifted as a results of the binding of MphR(A) decreased as the concentration of erythromycin was increased. These results indicate that transcription of the mph(A)-mrx-mphR(A) operon is negatively regulated by the binding of a repressor protein, MphR(A), to the promoter of the mph(A) gene and is activated upon inhibition of binding of MphR(A) to the promoter in the presence of erythromycin.

Clinical pharmacokinetics of clarithromycin

Clarithromycin is a macrolide antibacterial that differs in chemical structure from erythromycin by the methylation of the hydroxyl group at position 6 on the lactone ring. The pharmacokinetic advantages that clarithromycin has over erythromycin include increased oral bioavailability (52 to 55%), increased plasma concentrations (mean maximum concentrations ranged from 1.01 to 1.52 mg/L and 2.41 to 2.85 mg/L after multiple 250 and 500 mg doses, respectively), and a longer elimination half-life (3.3 to 4.9 hours) to allow twice daily administration. In addition, clarithromycin has extensive diffusion into saliva, sputum, lung tissue, epithelial lining fluid, alveolar macrophages, neutrophils, tonsils, nasal mucosa and middle ear fluid. Clarithromycin is primarily metabolised by cytochrome P450 (CYP) 3A isozymes and has an active metabolite, 14-hydroxyclarithromycin. The reported mean values of total body clearance and renal clearance in adults have ranged from 29.2 to 58.1 L/h and 6.7 to 12.8 L/h, respectively. In patients with severe renal impairment, increased plasma concentrations and a prolonged elimination half-life for clarithromycin and its metabolite have been reported. A dosage adjustment for clarithromycin should be considered in patients with a creatinine clearance < 1.8 L/h. The recommended goal for dosage regimens of clarithromycin is to ensure that the time that unbound drug concentrations in the blood remains above the minimum inhibitory concentration is at least 40 to 60% of the dosage interval. However, the concentrations and in vitro activity of 14-hydroxyclarithromycin must be considered for pathogens such as Haemophilus influenzae. In addition, clarithromycin achieves significantly higher drug concentrations in the epithelial lining fluid and alveolar macrophages, the potential sites of extracellular and intracellular respiratory tract pathogens, respectively. Further studies are needed to determine the importance of these concentrations of clarithromycin at the site of infection. Clarithromycin can increase the steady-state concentrations of drugs that are primarily depend upon CYP3A metabolism (e.g., astemidole, cisapride, pimozide, midazolam and triazolam). This can be clinically important for drugs that have a narrow therapeutic index, such as carbamazepine, cyclosporin, digoxin, theophylline and warfarin. Potent inhibitors of CYP3A (e.g., omeprazole and ritonavir) may also alter the metabolism of clarithromycin and its metabolites. Rifampicin (rifampin) and rifabutin are potent enzyme inducers and several small studies have suggested that these agents may significantly decrease serum clarithromycin concentrations. Overall, the pharmacokinetic and pharmacodynamic studies suggest that fewer serious drug interactions occur with clarithromycin compared with older macrolides such as erythromycin and troleandomycin.

Interpretation of middle ear fluid concentrations of antibiotics: comparison between ceftibuten, cefixime and azithromycin

AIMS

The aim of this study was to determine the potential influence of variables such as the cell content in the fluid, and serum levels, on the concentrations of ceftibuten, cefixime and azithromycin in the middle ear fluid of patients suffering from acute otitis media.

METHODS

This randomized, open study compared the penetration of ceftibuten (9 mg kg(-1) 18 patients), cefixime (8 mg kg(-1), 16 patients) and azithromycin (10 mg kg(-1) 16 patients) into the intracellular and extracellular compartments of middle ear fluid of 50 paediatric patients (aged 8-14 years) with acute otitis media. Middle ear fluid was extracted by tympanocentesis 4, 12 and 24 h after dosing and divided into two fractions: with cells (as collected) (C+) and cell-free (C-). Antibiotics were assayed in C+ and C- samples by h.p.l.c.

RESULTS

Ceftibuten achieved greater penetration into middle ear fluid than cefixime and azithromycin. Higher concentrations of ceftibuten (CTB) and cefixime (CFX) were found in the C- fraction (CTB: 4h 13.3+/-1.86; 12h 4.7+/-1.18; 24h 0.5+/-0.2. CFX: 4h 3.2+/-1.4; 12h 1.5+/-0.5; 24h>(0.1 mgl(-1)) than in the C+ fraction (CTB:4 h 8.4+/-4.3; 12 h 2.88+/-1.19; 24 h 0.3+/-0.27. CFX: 4 h 1.2+/-0.6; 12 h 0.8+/-0.2; 24 h>0.1 mg l(-1)) at the each time point, while the opposite was true for azithromycin (C-: 4 h 0.11+/-0.04; 12 h 0.12+/-0.08; 24 h 0.23+/-0.12. C+: 4 h 0.38+/-0.24; 12 h 0.9+/-0.03; 24 h 1.05+/-0.3 mg l(-1)).

CONCLUSIONS

This study demonstrates that the penetration of antibiotics into the middle ear fluid is influenced by its serum concentrations as well as by the cell content in the fluid. Ceftibuten achieved higher middle ear fluid concentrations than cefixime in C+ and C- fractions at all time points. Both ceftibuten and cefixime concentrations are negatively influenced by the cell content in the fluid. In contrast the concentration of azithromycin to the middle ear fluid is positively influenced by the cell content in the fluid.

Comparative tolerability of erythromycin and newer macrolide antibacterials in paediatric patients

The macrolides are a well established group of antibacterials frequently used in general practice. The most frequently used macrolides in paediatric patients are erythromycin, a naturally occurring compound, and clarithromycin and azithromycin, recently developed macrolides. Overall adverse effect rates of 7 to 26% for erythromycin, 14 to 26% for clarithromycin, and 6 to 27% for azithromycin have been described in children. Adverse gastrointestinal effects, including nausea, vomiting, diarrhoea and abdominal cramps, are the most common problems in children. Allergic reactions, hepatotoxicity, ototoxicity and adverse effects involving the central and peripheral nervous systems have also been observed in children. Stevens-Johnson, Schonlein-Henoch and Churg-Strauss syndromes have been rarely described in children. Treatment-related laboratory abnormalities have been recorded in 2 to 4% of erythromycin- and in 0 to 1% of both clarithromycin- and azithromycin-treated children. Elevation in liver function tests was the most common abnormality cited. Increased macrolide use in children in recent years has resulted in a growing potential for drug interactions between them and other pharmacologically active agents via the inhibition of cytochrome P450 (CYP) microsomal enzymes. Drug interactions with theophylline, cyclosporin, carbamazepine, terfenadine and warfarin limit erythromycin use. Clarithromycin is a weak inducer of CYP and exhibits fewer drug-drug interactions than erythromycin. However, its use with theophylline, carbamazepine and terfenadine is contraindicated. In contrast, no significant interactions have been reported with azithromycin to date. Macrolides have been proven to be well tolerated in the treatment of upper and lower respiratory tract infections, skin and soft tissue infections, and also in less frequent infections occurring in paediatric patients. In addition, clarithromycin and azithromycin have shown good tolerability profiles in immunocompromised paediatric patients. In conclusion, macrolides antibacterials have proven to be well tolerated in paediatric patients. Although the incidence of adverse effects is similar with the use of erythromycin and the newer macrolides, drug interactions occur significantly less when clarithromycin or azithromycin are administered.

Safety and efficacy of azithromycin in the treatment of community-acquired pneumonia in children

OBJECTIVE

To compare the safety and efficacy of azithromycin with amoxicillin/clavulanate or erythromycin for the treatment of community-acquired pneumonia, including atypical pneumonia caused by Mycoplasma pneumoniae and Chlamydia pneumoniae.

METHODS

Multicenter, parallel group, double blind trial in which patients 6 months to 16 years of age with community-acquired pneumonia were randomized 2:1 to receive either azithromycin for 5 days or conventional therapy for 10 days (amoxicillin/clavulanate if < or =5 years of age or erythromycin estolate if >5 years of age). Patients from 23 geographically diverse sites were evaluated for clinical outcomes and/or adverse events at Days 3 to 5, Days 15 to 19 and 4 to 6 weeks posttherapy. Microbiology (culture or polymerase chain reaction) was done at baseline and Days 15 to 19 for bacteria, Chlamydia pneumoniae and Mycoplasma pneumoniae. Serology for C. pneumoniae and M. pneumoniae was done at baseline and 4 to 6 weeks posttherapy.

RESULTS

Of 456 patients enrolled during 17 consecutive months, 420 were evaluable. Clinical success at Study Days 15 to 19 was 94.6% in the azithromycin group and 96.2% in the comparative treatment group (P = 0.735) and at 4 to 6 weeks posttherapy 90.6 and 87.1%, respectively (P = 0.330). Evidence of infection was identified in 46% of 420 evaluable patients (1.9% bacteria, 29.5% M. pneumoniae and 15% C. pneumoniae). Microbiologic eradication was 81% for C. pneumoniae and 100% for M. pneumoniae in the azithromycin group vs. 100 and 57%, respectively, in the comparator group. Treatment-related adverse events occurred in 11.3% of the azithromycin group and 31% in the comparator group (P < 0.05).

CONCLUSION

Azithromycin used once daily for 5 days produced a satisfactory therapeutic outcome similar to those of amoxicillin/clavulanate or erythromycin given three times a day for 10 days for treatment of community-acquired pneumonia. Azithromycin had significantly fewer side effects than comparator drugs.

The acceptability, efficacy and safety of a new paediatric oral suspension of roxithromycin in respiratory tract infections

A new paediatric formulation of roxithromycin was tested for acceptability, efficacy and safety in a multicentre, prospective, non-comparative trial in 210 children, aged between 2 and 8 years, with a variety of respiratory tract infections. Most children were diagnosed as having rhinobronchitis, acute pharyngitis or acute tonsillitis. A dose of 5-8 mg/kg/day (mean +/- SD, 5.92 +/- 1.12) roxithromycin was given orally for 5-10 days (mean +/- SDL 6.86 +/- 1.80). The formulation consists of a tablet for suspension in a small volume of water, administered using a spoon, twice daily. Acceptability was good, with only eight children refusing their medication because of the taste or because of vomiting. The method of administration was found to be convenient by 76% of parents. The clinical success rate was 89.1% in the intent-to-treat analysis. There were only 18 adverse events reported by 14 patients; of these, only 10 events (all gastrointestinal) in eight patients were classified as drug related. A total of eight patients discontinued treatment because of an adverse event, but in only four were the events drug related.

History of antibiotic treatment and prevalence of H. pylori infection among children: results of a population-based study

We investigated the association of commonly prescribed antibiotics with the prevalence of current Helicobacter pylori infection among children. All children who were screened in 1996 for school fitness by physicians of the Public Health Service in Ulm, a city in the south of Germany, were invited to participate in the study. Infection status was determined by 13C-urea breath test. In addition, the parents of the children were asked to fill out a standardized questionnaire. Nine hundred forty-five out of the 1201 eligible children participated in the study (response rate = 79%). The children were aged 5 to 8 years. Seventeen children who were receiving antibiotics at the day of the breath test were excluded from the analysis. Overall, for 683 children (73.6%) a prior usage of antibiotics was reported. Prevalence of H. pylori infection was significantly lower in children with reported antibiotic usage (odds ratio = 0.46; 95% CI, 0.27-0.76 after adjustment for confounders). Our results suggest that information on prior usage of antibiotics should always be considered in studies evaluating prevalence and risk factors of H. pylori infection in children.

History of macrolide use in pediatrics

Erythromycin, the prototypical macrolide, has been widely used since the 1950s in the management of pediatric infections. Erythromycin is the drug of choice for infants and children with Legionnaire's disease, pertussis, diphtheria, lower respiratory tract infections caused by Mycoplasma pneumoniae, Chlamydia pneumoniae and Chlamydia trachomatis and enteritis caused by Campylobacter jejuni. It is also indicated for treatment of syphilis; for streptococcal, staphylococcal and pneumococcal infections; genital infections caused by Ureaplasma urealyticum; and for the prevention of rheumatic fever and endocarditis in patients who are allergic to beta-lactam antibiotics. The new macrolides azithromycin and clarithromycin are also active against Borrelia burgdorferi, Helicobacter pylori, Mycobacterium avium-intracellulare complex, Cryptosporidium spp. and Toxoplasma gondii. Erythromycin is associated with a low risk of serious side effects, although gastric distress occurs in a significant proportion of patients. Drug interactions with theophylline, carbamazepine, warfarin, cyclosporine, terfenadine and digoxin limit erythromycin use. The newer macrolides azithromycin and clarithromycin are more stable, better absorbed and better tolerated than erythromycin. Azithromycin is more active than erythromycin against Haemophilus influenzae. Excellent tissue and intracellular penetration may contribute to their clinical efficacy. In children both azithromycin and clarithromycin are indicated for acute otitis media caused by Streptococcus pneumoniae, H. influenzae and Moraxella catarrhalis and for pharyngitis/tonsillitis caused by Streptococcus pyogenes. (As of December, 1996, azithromycin for oral suspension was approved for community-acquired pneumonia in children caused by C. pneumoniae, H. influenzae, M. pneumoniae and S. pneumoniae.) Claritromycin is also indicated for acute maxillary sinusitis, uncomplicated skin and skin structure infections, pneumonia and disseminated mycobacterial infections. Azithromycin and clarithromycin are associated with a lower incidence of gastrointestinal side effects, a low rate of drug discontinuation caused by side effects and a low potential for interaction with other drugs.