Azithromycin. A review of its pharmacological properties and use as 3-day therapy in respiratory tract infections

Tissue disposition of azithromycin after intravenous and intramuscular administration to rabbits

Tissue disposition of azithromycin after intravenous (IV) or intramuscular (IM) injection at a single dose rate of 10mg/kg bodyweight were investigated in rabbits using a modified agar diffusion bioassay for determining tissue concentrations. The pharmacokinetic behaviour of azithromycin was characterized by low and sustained plasma concentrations but high and persistent tissue concentrations. Kinetic parameters indicated a high retention of the drug in peripheral compartments. The plasma half-lives after IV and IM administrations were similar being 21.8h and 23.1h, respectively, while the half-lives obtained in tissues after IV and IM administration were at least 1.4 and 1.9 times longer than in plasma, respectively. The highest tissue concentrations were found in bile, liver and spleen whereas the lowest ones were found in skeletal muscle (although they were higher than those in plasma). From the results of the single administration in this study an IM dosage regimen can be proposed that achieves minimum concentrations over 2mg/L in rabbits: three doses of 4-5mg/kg/day would provide suitable therapeutic concentrations in pulmonary tissues over seven days.

Pharmacokinetics and tissue tolerance of azithromycin after intramuscular administration to rabbits

The pharmacokinetics of azithromycin after intravenous and intramuscular injection at a single dose rate of 10mg/kg bodyweight were investigated in rabbits by using a modified agar diffusion bioassay for determining plasma concentrations. The plasma creatine kinase activity was determined after i.m. administration for the evaluation of the tissue tolerance. The elimination half-lives of azithromycin after intravenous and intramuscular administration were 24.1 and 25.1h, respectively. After intramuscular administration mean peak plasma concentration was 0.26+/-0.01 mg/L and bioavailability was 97.7%. Plasma CK activity rose sharply within 8h after i.m. injection of azithromycin; activity returned to pre-treatment level by 48-72 h post-treatment. The transient rise in serum CK activity indicates some degree of muscle tissue damage at the injection site.

Validated HPLC–MS–MS method for determination of azithromycin in human plasma

A validated, highly sensitive, and selective HPLC method with MS-MS detection has been developed for quantitative determination of azithromycin (AZI) in human Na2EDTA plasma. Roxithromycin (ROX) was used as internal standard. Human plasma containing AZI and internal standard was ultrafiltered through Centrifree Micropartition devices and the concentration of AZI was determined by isocratic HPLC-MS-MS. Multiple reaction monitoring mode (MRM) was used for MS-MS detection. The calibration plot was linear in the concentration range 2.55-551.43 ng mL(-1). Inter-day and Intra-day precision and accuracy of the proposed method were characterized by R.S.D and percentage deviation, respectively; both were less than 8%. Limit of quantification was 2.55 ng mL(-1). The proposed method was used to determine the pharmacokinetic profile of AZI (250-mg tablets).

Possible azithromycin-associated hiccups

OBJECTIVE

To report a case of persistent hiccups associated by azithromycin therapy.

CASE SUMMARY

A 76-year-old man presented with persistent hiccups after beginning azithromycin for the treatment of pharyngitis. Hiccups were persistent and exhausting. Discontinuation of azithromycin and therapy with baclofen finally resolved hiccups. No organic cause of hiccups was identified despite extensive investigation.

DISCUSSION

Pharmacotherapeutic agents have been uncommonly associated with hiccups. Corticosteroids (dexamethasone and methylprednisolone), benzodiazepines (midazolam) and general anaesthesia have been the specific agents mentioned most frequently in the literature as being associated with the development of hiccups. Few cases of drug-induced hiccups have been reported related to macrolide antimicrobials. Using the Naranjo adverse effect reaction probability scale this event could be classified as possible (score 5 points), mostly because of the close temporal sequence, previous reports on this reaction with other macrolides and the absence of any alternative explanation for hiccups. Our hypothesis is that a vagal mechanism mediated by azithromycin could be the pathogenesis of hiccups in our patient.

CONCLUSIONS

Diagnosis of drug-induced hiccups is difficult and often achieved only by a process of elimination. However, macrolide antimicrobials have been reported to be associated with hiccups and vagal mechanism could explain the development of this side-effect.

Enhanced efficacy of single-dose versus multi-dose azithromycin regimens in preclinical infection models

OBJECTIVES

As a result of the prolonged half-life and unique pharmacokinetic and pharmacodynamic (PK-PD) characteristics of azithromycin, shorter dosing regimens are being evaluated for the treatment of community-acquired infections. To provide further support for a shorter dosing regimen, the efficacy of azithromycin was determined in preclinical infection models comparing single- versus multi-dose regimens.

METHODS

The efficacy of single versus multi-dose regimens of azithromycin was compared in mouse pneumonia, acute peritonitis, and neutropenic thigh infection models and in a gerbil model of Haemophilus influenzae acute otitis media. Azithromycin was administered as a single oral dose on the first treatment day, or as two divided doses over 2 treatment days, or as three divided doses over 3 treatment days. The pharmacokinetics of azithromycin was profiled following single and multi-dose regimens with the single dose data fit to an Emax model to characterize the PK-PD of azithromycin.

RESULTS

In the mouse efficacy models, administration of single-dose azithromycin produced superior rates of survival and bacterial clearance compared with the same total dose divided over 2 or 3 days. In the gerbil model, a single dose sterilized the middle ear and more rapidly cleared H. influenzae. The pharmacokinetic evaluation confirmed similar total exposure (AUC) in serum and pulmonary tissue for the three regimens. Correlation of PK-PD parameters and antimicrobial efficacy confirmed a concentration-dependent and dosing-independent relationship for azithromycin.

CONCLUSIONS

These data are consistent with data reported from clinical studies and indicate that a single-dose regimen would be at least as effective as the same dose administered over several days.

Secondary prevention of atherosclerosis through chlamydia pneumoniae eradication (SPACE Trial): a randomised clinical trial in patients with peripheral arterial disease

BACKGROUND

Sero-epidemiological and experimental studies suggest that Chlamydia pneumoniae infections play an important role in the development of atherosclerosis. Clinical trials have shown contradictory results regarding the efficacy of antibiotics to prevent atherosclerosis-related complications in patients with coronary artery disease. Our aim was to study the effect of a short course of azithromycin on the incidence of cardiovascular events and peripheral vascular function in patients with stable peripheral arterial disease (PAD).

PATIENTS AND METHODS

Five hundred and nine PAD-patients were randomised to receive either a 3-day course of azithromycin (500 mg daily) or placebo, with 2 years of follow-up. C. pneumoniae serology was determined at baseline. Clinical endpoints were death, coronary events (myocardial infarction, unstable angina, and/or coronary revascularization procedures), cerebral events (stroke, TIA, and/or carotid endarterectomy) and peripheral arterial complications (increased PAD-symptoms with decreased ankle-brachial index (ABPI, 0.1-point decrease after 12 months), and/or peripheral revascularization procedures).

RESULTS

Five hundred and nine patients (160 women) with an atherosclerotic risk factor profile were randomised, 257 patients to azithromycin and 252 to placebo. Four hundred and forty nine patients (88%) had intermittent claudication and 60 (12%) had critical limb ischemia. By 24-month follow up, 182 patients (36%) developed 252 complications (45 deaths, 34 coronary events, 34 cerebral events and 139 peripheral arterial complications). C. pneumoniae IgA-titres were associated with the development of cardiovascular events. Nevertheless, the number of complications (131 in the azithromycin group vs. 121 in the placebo group) and the number of patients that developed complications (98 (38%) in the azithromycin vs. 84 (33%) in the placebo group) was comparable in both treatment groups. Life table analysis showed no effect of azithromycin on survival or ABPI.

CONCLUSION

A short-term course of azithromycin offers no benefits for survival or ankle pressure in PAD-patients.

[Pharmacokinetic/pharmacodynamic analysis of antibiotic therapy in dentistry and stomatology]

INTRODUCTION

This study evaluates the efficacy of various antimicrobial treatments for orofacial infections on the basis of pharmacokinetic/pharmacodynamic (PK/PD) criteria.

METHODS

A complete a literature search was undertaken to establish the MIC90 values of the five microorganisms most frequently isolated in odontogenic infections and the pharmacokinetic parameters of 13 antibiotics used in these infections. Pharmacokinetic simulations were then carried out with mean population parameters and efficacy indexes were calculated for the 47 treatment regimens analyzed. For drugs showing time-dependent antibacterial killing, the time above MIC (t > MIC) was calculated. For drugs with concentration-dependent bactericidal activity, the AUC/MIC was calculated.

RESULTS

Amoxicillin-clavulanic (500 mg/8 h or 1000 mg/12 h) and clindamycin (300 mg/6 h) in the time-dependent killing group and moxifloxacin (400 mg/24 h) in the concentration-dependent group showed adequate efficacy indexes against the five pathogens considered to be the most commonly implicated in odontogenic infections. The spiramycin plus metronidazole combination, present in the commercial formulation Rhodogyl, did not reach satisfactory PK/PD indexes.

CONCLUSION

PK/PD indexes, which are useful predictors of the potential efficacy of antibacterial therapy, were used with ontogenic infections in the present study. The PK/PD simulations showed that amoxicillin-clavulanic, clindamycin and moxifloxacin were the most suitable antibiotics for this kind of infection. Clinical trials are required to confirm that this methodology is useful in these pathologic processes.

Pharmacokinetic/Pharmacodynamic Evaluation of Antimicrobial Treatments of Orofacial Odontogenic Infections

OBJECTIVE

To evaluate the efficacy of antimicrobial therapy in oral odontogenic infections using estimated pharmacokinetic/pharmacodynamic parameters or efficacy indices, and to compare pharmacokinetic/pharmacodynamic breakpoints with National Committee for Clinical Laboratory Standards' (NCCLS) breakpoints.

STUDY DESIGN

Retrospective literature search to obtain minimum inhibitory concentration (MIC) values, pharmacokinetic parameters of antimicrobials and NCCLS breakpoints. Pharmacokinetic simulations were carried out using WinNonlin software (Pharsight Corporation, Mountain View, CA, USA).

METHODS

For antimicrobials with time-dependent activity, the time that the plasma drug concentration exceeds the MIC as the percentage of dose interval at steady state was calculated. For antimicrobials with concentration-dependent activity, the total area under the plasma concentration-time curve over 24 hours at steady state divided by the MIC was calculated. Pharmacokinetic/pharmacodynamic breakpoints were calculated according to these parameters.

RESULTS

Only amoxicillin/clavulanic acid and clindamycin showed adequate efficacy indices against the most commonly isolated bacteria in odontogenic infections. Metronidazole reached good indices against anaerobes only. Pharmacokinetic/pharmacodynamic susceptibility breakpoints do not coincide exactly with NCCLS breakpoints.

CONCLUSION

Owing to the scarcity of double-blind, clinical trials on the use of antimicrobials in endodontics, this study may be useful in determining the best antimicrobial treatment in these infections. However, as we have not used concentration data in infected tissue to determine pharmacokinetic/pharmacodynamic indices, it would be necessary to design clinical trials in order to confirm these results.

Macrolides and ketolides: azithromycin, clarithromycin, telithromycin

The advanced macrolides, azithromycin and clarithromycin, and the ketolide telithromycin are structural analogues of erythromycin. They have several distinct advantages when compared with erythromycin including enhanced spectrum of activity, more favorable pharmacokinetics and pharmacodynamics, once daily administration, and improved tolerability. This article reviews the pharmacokinetics, antimicrobial activity, clinical use, and adverse effects of these antimicrobial agents.

Azithromycin for acute lower respiratory tract infections

BACKGROUND

The spectrum of acute lower respiratory tract infection ranges from acute bronchitis and acute exacerbations of chronic bronchitis to pneumonia. Annually approximately five million people die of acute respiratory tract infections. Among these, pneumonia represents the most frequent cause of mortality, hospitalization and medical consultation. Azithromycin is a new macrolide antibiotic, structurally modified from erythromycin and is noted for its activity against some gram-negative organisms associated with respiratory tract infections, particularly Haemophilus influenzae (H. influenzae).

OBJECTIVES

To compare the effectiveness of azithromycin to amoxycillin or amoxycillin/clavulanic acid (amoxyclav) in the treatment of LRTI, in terms of clinical failure, incidence of adverse events and microbial eradication.

SEARCH STRATEGY

We searched the Cochrane Central Register of Controlled Trials (CENTRAL) (The Cochrane Library Issue 4, 2003), MEDLINE (January 1966 to January Week 3, 2004), and EMBASE (January 1988 to 2003).

SELECTION CRITERIA

Randomised and quasi-randomised controlled trials, which compared azithromycin to amoxycillin or amoxycillin/clavulanic acid in patients with clinical evidence of acute LRTI: acute bronchitis, pneumonia, and acute exacerbation of chronic bronchitis were studied.

DATA COLLECTION AND ANALYSIS

The criteria for assessing study quality were generation of allocation sequence, concealment of treatment allocation, blinding, and completeness of the trial. All types of acute lower respiratory tract infections were initially pooled in the meta-analyses. Funnel plot was used to examine publication bias. The heterogeneity of results was investigated by the forest plot and Chi-square test. Index of I(2) was also used to measure inconsistency results among trials. Subgroup analysis was conducted for age, types of respiratory tract infection and types of antibiotic in control groups. Sensitivity analysis was conducted under the condition of trial size and concealment of treatment allocation.

MAIN RESULTS

Fourteen trials with 2,521 enrolled patients used 2,416 patients in the analysis. A total of 1,350 patients received azithromycin and 1,066 received amoxicillin or amoxicillin-clavulanic acid. The pooled analysis of all trials showed that there was no significant difference in the incidence of clinical failure on about day 10 to 14 after therapy started between the two groups (relative risk (RR) (random effects) 0.96; 95% CI 0.58 to 1.57). Sensitivity analysis showed that a reduction of clinical failure in azithromycin-treated patients (RR 0.52; 95% CI 0.24 to 1.12) in three adequately concealed studies, compared to RR 1.14 (95% CI 0.62 to 2.08) in eleven studies with inadequate concealment. Eleven trials reported the incidence of microbial eradication and there was no significant difference between the two groups (RR 0.98; 95% CI 0.91 to 1.07). The reduction of adverse events in azithromycin group was RR 0.75 (95% CI 0.56 to 1.00).

REVIEWERS' CONCLUSIONS

There is unclear evidence that azithromycin is superior to amoxicillin or amoxicillin-clavulanic acid in treating acute LRTI. Future trials with high methodological quality are needed.

Efficacy and tolerability of once-daily oral telithromycin compared with clarithromycin for the treatment of community-acquired pneumonia in adults

BACKGROUND

Telithromycin is a new antibacterial agent of the ketolide class designed to provide optimal treatment against common bacterial respiratory tract pathogens. Telithromycin was derived by structural modification of the basic macrolide molecule to allow tight binding to the bacterial ribosome that enhances potency and minimizes the risk for the development of resistant strains.

OBJECTIVE

The aim of this study was to compare the efficacy and tolerability of telithromycin 800 mg once daily with those of high-dose clarithromycin (500 mg twice daily), each for 10 days, in the treatment of adult patients with community-acquired pneumonia (CAP).

METHODS

This randomized, double-blind, double-dummy, parallel-group clinical trial was conducted at 54 centers in the United States, Canada, Argentina, and Chile. Patients aged >or=18 years with acute CAP were randomized to receive 10-day treatment with oral telithromycin 800 mg once daily (administered as two 400-mg encapsulated tablets in the morning) and placebo (administered as 2 encapsulated tablets identical to the telithromycin in the evening) or high-dose clarithromycin (500 mg administered as two 250-mg identical encapsulated tablets twice daily). The primary outcome measure was clinical outcome at the posttherapy, test-of-cure visit (days 17-24 after the completion of therapy) in the clinically assessable per-protocol population. Secondary efficacy variables included bacteriologic outcome at the posttherapy, test-of-cure visit, and clinical and bacteriologic outcomes at the late posttherapy visit (day 31-45). Tolerability was assessed using investigator observation, patient self-reporting, clinical laboratory data, a 12-lead electrocardiogram, and physical examination (including vital signs).

RESULTS

A total of 493 patients were enrolled and 448 patients received >or=1 dose of study medication (224 patients/group). A diagnosis of CAP was confirmed in 416 patients (205 men, 211 women; median age, 43 years; telithromycin, n = 204; clarithromycin, n = 212). Clinical cure rates were 88.3% (143/162) in the telithromycin group and 88.5% ( 138/56) in the clarithromycin group. Bacterial eradication rates were comparable between treatment groups (telithromycin, (28/32) [87.5%]; clarithromycin, (29/30) [96.7%]. Both treatment were fairly well tolerated; adverse events were experienced in 57.0% of the patients treated with telithromycin and 49.1% of those treated with clarithromycin; most of these were assessed as mild.

CONCLUSIONS

In this study of adult patients with CAP, telithromycin 800 mg once daily was an effective and fairly well-tolerated regimen for initial empiric treatment, with clinical and bacteriologic efficacy and tolerability equivalent to therapy with high-dose clarithromycin (500 mg twice daily).

Pharmacokinetic evaluation of an azithromycin controlled release dosage form in healthy human volunteers: a single dose study

Azithromycin (AZI) follows a two-compartment model pharmacokinetically. The purpose of this study was to evaluate the in vivo performance of a controlled release (CR) formulation of AZI, which would eliminate the risk of high peak plasma concentrations obtained within 2-3 h after peroral administration of immediate release (IR) products. The study was conducted in twelve healthy male human volunteers to compare an experimental NIPER product (CR tablets) with Vicon (IR tablets) at the same dose level as a single-dose, randomized, one-period, two-treatment, and parallel-study. Concentrations of AZI in serum samples were assessed using the validated HPLC method. From the serum concentration-time profiles various pharmacokinetic parameters (AUC(0-96), AUC(0-inf), C(max) and T(max)) were calculated for both products. Results showed that the high peak concentration obtained by administration of a conventional IR formulation were eliminated with the CR product. A mean dosage form index (DI) of 1.17 with fluctuations of 7.57% was obtained with the CR product at steady state level, indicating reduced fluctuations at the steady state serum concentrations. Elimination of the pronounced peak as well as fluctuations reduced or minimized AZI adverse effects associated with the IR product.

Impact of pharmacodynamics on dosing of macrolides, azalides, and ketolides

The study of pharmacodynamics characterizes the relationship between changing drug concentrations over time and antimicrobial and toxicologic effects and thereby offers a targeted approach to the design of dosing regimens for many antimicrobials. Distinct patterns of antimicrobial dynamics have been elucidated from these relationships and pharmacodynamic parameters (peak-MIC, AUC-MIC, T > MIC) have been used to quantify antimicrobial effects in relation to drug exposure. These relationships can be used to predict efficacy of a given dosing regimen. The accuracy of these predictions is influenced, in part, by the completeness of the model in which they are studied. This article discusses various in vitro and in vivo studies and clinical data that have contributed to the understanding of pharmacodynamics of the macrolides, azalides, and ketolides.

Single-Dose Azithromycin for Respiratory Tract Infections

OBJECTIVE

To describe the pharmacology, efficacy, and safety data of the use of single-dose azithromycin for respiratory tract infections in children and adults.

DATA SOURCES

A MEDLINE search (1990–September 2003) was performed to identify all pertinent studies and review articles. When appropriate information was not available in the literature, data were obtained from the product manufacturers or abstracts from international conferences.

STUDY SELECTION AND DATA EXTRACTION

All available studies were reviewed to provide pharmacokinetic, pharmacodynamic, efficacy, and safety data on use of single-dose azithromycin for respiratory tract infections.

DATA SYNTHESIS

Several studies have demonstrated that shorter regimens of azithromycin (1500 mg over 3 day vs 5 day or single dose vs 3 day) provide higher serum exposures compared with the longer regimens. This makes it possible to give the same dose over a shorter period of time and achieve the same efficacy with the potential for enhanced adherence. Single-dose azithromycin 30 mg/kg was approved in 2003 for treatment of acute otitis media (AOM) in children. Studies have demonstrated that, when administering azithromycin as a single dose, its efficacy and safety are comparable to that of other standard regimens for AOM. Single-dose regimens for treatment of respiratory tract infections in adults have not been studied widely, with only 2 studies being conducted for treatment of community-acquired pneumonia and one study for treatment of tonsillitis; all demonstrated at least equal efficacy with the single-dose regimen compared with comparators given for longer periods of time.

CONCLUSION

Available data regarding single-dose azithromycin are promising. Although use of this regimen in children is warranted based on studies to date, additional large-scale trials are needed prior to mainstream use of the regimen in adults.

New Developments in Antibacterial Choice for Lower Respiratory Tract Infections in Elderly Patients

Elderly patients are at increased risk of developing lower respiratory tract infections compared with younger patients. In this population, pneumonia is a serious illness with high rates of hospitalisation and mortality, especially in patients requiring admission to intensive care units (ICUs). A wide range of pathogens may be involved depending on different settings of acquisition and patient's health status. Streptococcus pneumoniae is the most common bacterial isolate in community-acquired pneumonia, followed by Haemophilus influenzae, Moraxella catarrhalis and atypical pathogens such as Chlamydia pneumoniae, Legionella pneumophila and Mycoplasma pneumoniae. However, elderly patients with comorbid illness, who have been recently hospitalised or are residing in a nursing home, may develop severe pneumonia caused by multidrug resistant staphylococci or pneumococci, and enteric Gram-negative bacilli, including Pseudomonas aeruginosa. Moreover, anaerobes may be involved in aspiration pneumonia. Timely and appropriate empiric treatment is required in order to enhance the likelihood of a good clinical outcome, prevent the spread of antibacterial resistance and reduce the economic impact of pneumonia. International guidelines recommend that elderly outpatients and inpatients (not in ICU) should be treated for the most common bacterial pathogens and the possibility of atypical pathogens. The algorithm for therapy is to use either a selected beta-lactam combined with a macrolide (azithromycin or clarithromycin), or to use monotherapy with a new anti-pneumococcal quinolone, such as levofloxacin, gatifloxacin or moxifloxacin. Oral (amoxicillin, amoxicillin/clavulanic acid, cefuroxime axetil) and intravenous (sulbactam/ampicillin, ceftriaxone, cefotaxime) beta-lactams are agents of choice in outpatients and inpatients, respectively. For patients with severe pneumonia or aspiration pneumonia, the specific algorithm is to use either a macrolide or a quinolone in combination with other agents; the nature and the number of which depends on the presence of risk factors for specific pathogens. Despite these recommendations, clinical resolution of pneumonia in the elderly is often delayed with respect to younger patients, suggesting that optimisation of antibacterial therapy is needed. Recently, some new classes of antibacterials, such as ketolides, oxazolidinones and streptogramins, have been developed for the treatment of multidrug resistant Gram-positive infections. However, the efficacy and safety of these agents in the elderly is yet to be clarified. Treatment guidelines should be modified on the basis of local bacteriology and resistance patterns, while dosage and/or administration route of each antibacterial should be optimised on the basis of new insights on pharmacokinetic/pharmacodynamic parameters and drug interactions. These strategies should be able to reduce the occurrence of risk factors for a poor clinical outcome, hospitalisation and death.

A guide to selection and appropriate use of macrolides in skin infections

Dermatologists must be aware of the adverse effects of antimicrobial agents as well as various drug interactions that may influence the choice of drug as well as specific drug schedules. The development of modern antibacterials has improved the treatment of cutaneous bacterial infections. Macrolide antibacterials continue to be an important therapeutic class of drugs with established efficacy in a variety of skin infections. All macrolides inhibit protein synthesis by reversibly binding to the 23S ribosomal RNA in the 50S-subunit. Erythromycin, the prototype of macrolide antibacterials, was isolated from the metabolic products of a strain of Streptomyces erytherus in 1952. Originally, erythromycin was introduced as an alternative to penicillin because of its activity against the Gram-positive organisms. Numerous studies have demonstrated the efficacy and safety of erythromycin for various infectious diseases. Unfortunately, erythromycin is associated with a number of drawbacks including a narrow spectrum of activity, unfavorable pharmacokinetic properties, poor gastrointestinal tolerability, and a significant number of drug-drug interactions. Newer macrolides have been developed to address these limitations. The pharmacokinetics of azithromycin and clarithromycin allow for shorter dosing schedules because of prolonged tissue levels. The efficacy of azithromycin for the treatment of skin and soft tissue infections in adults and children is well established. The unique pharmakinetics of azithromycin makes it a suitable agent for the treatment of acne. Clarithromycin represents a clear advance in the macrolide management of patients with leprosy and skin infections with atypical mycobacteria. Dirithromycin and roxithromycin display no clinical or bacteriological adcantage over erythromycin despite a superior pharmacokinetic profile. An area of concern is the increasing macrolide resistance that is being reported with some of the common pathogens which may limit the clinical usefulness of this class of antimicrobial agents in future.

Voltammetric assay of azithromycin in pharmaceutical dosage forms

The oxidative behaviour of azithromycin was studied at s glassy carbon electrode in different buffer system using cyclic, linear sweep and differential pulse voltammetry. The oxidation process was shown to be irreversible over the entire pH range studied (5-11) and was diffusion-adsorption controlled. Analytical method with adequate precision and accuracy was developed for the determination of azithromycin in phosphate buffer at pH 7 as supporting electrolyte containing 10% methanol and 0.05 M ammonium acetate. The peak current varied linearly with azithromycin concentration in the range 1-15 microg/ml. The procedure was successfully applied for assay of the drug in the pharmaceutical dosage forms. The relative standard deviation (n = 5) of 2.18% was obtained.

Does short-course antibiotic therapy better meet patient expectations?

A pan-European market research study of 3254 patients designed to determine patient attitudes, expectations and behaviour to antibiotic management of mild-moderate RTIs, identified three key drivers of perceived antibiotic efficacy: length of antibiotic course, time to onset of symptom relief and time to complete resolution of symptoms. Azithromycin was selected as "drug therapy of shortest dosage schedule" for common outpatient infections. The results demonstrate that once-daily, short-course treatment is perceived to be significantly more effective than longer antibiotic courses and thus, better meets patient expectations of therapy. This perception of efficacy with short-course therapy also correlates with overall satisfaction with management by the physician and compliance with therapy. These findings have important implications for the way physicians manage patients with mild-moderate RTIs.

The evolution and role of macrolides in infectious diseases

Two of the most significant changes in the field of infectious disease management during the last few decades are the emergence of atypical and/or new pathogens that may have devastating consequences and the re-emergence of well-recognised organisms that have acquired antimicrobial resistance through a variety of mechanisms. Erythromycin, the prototype macrolide, was originally marketed approximately five decades ago as a useful alternative agent in the treatment of patients allergic to beta-lactam antibiotics. While clinically useful, its pharmacokinetic and adverse-event profile limited the use of erythromycin to these individuals. Enhancements of the macrolide structure circumvented many of the limitations of erythromycin and resulted in the development of azithromycin and clarithromycin. The clinical uses of clarithromycin and azithromycin are substantially wider than erythromycin due to the wide spectra of activity against the atypical and newer pathogens. In addition, these agents are well-tolerated and have a pharmacokinetic profile that allows once- or twice-daily administration. Studies also indicate that the more common of the two mechanisms of macrolide resistance in the US and Canada imparts only low-level resistance. The multitude of studies substantiating clinical as well as bacteriological success with these two agents indicates that, when used appropriately, they will stand the test of time and continue to be useful antimicrobial agents.

Characterization of azithromycin hydrates

Azithromycin (AZI) is a macrolide antibiotic with an expanded spectrum of activity that is commercially available as a dihydrate. This study was carried out to characterize hydrates of azithromycin. A commercial dihydrate sample was used to prepare monohydrate from water/ethanol (1:1) mixture. Hydrates were characterized using DSC, TGA, KFT, XRD, HSM, SEM and FT-IR. TGA showed that the commercial samples are dihydrate and the sample prepared from water/ethanol (1:1) was a monohydrate. Solubility studies revealed that monohydrate converted to dihydrate during solubility studies and as a result there was no significant difference in the equilibrium solubility of MH and DH. Thermal analysis under various conditions revealed that dehydration and melting took place simultaneously. Anhydrous AZI was found to be hygroscopic and converted to DH on storing at room temperature. Molecular modeling studies revealed the probable sites of attachment of water molecules to AZI.

Comparison of two dosages of azithromycin for three days versus penicillin V for ten days in acute group A streptococcal tonsillopharyngitis

BACKGROUND

Three-day, 10 mg/kg/day azithromycin (AZM) studies in pediatric acute group A streptococcal tonsillopharyngitis have shown contradictory bacteriologic results. This study investigates the efficacy and tolerability of two dosages of 3-day azithromycin (20 mg/kg/day and 10 mg/kg/day) compared with 10-day penicillin V.

METHODS

This was a prospective, comparative, randomized, multicenter trial. Children were scheduled to return for visits at 14 days (main end point) and 1 month after the onset of treatment for clinical and bacteriologic assessment. Molecular tools were used to compare pre- and posttreatment group A beta-hemolytic Streptococcus (GABHS) isolates.

RESULTS

Between November, 1997, and July, 1998, 501 patients (169 AZM 10 mg, 165 AZM 20 mg, 167 penicillin V) between 2 and 12 years old were enrolled; 500 were assessable for safety, 469 for intent to treat analysis and 420 for efficacy in the per protocol analysis. Before treatment 25 (7.9%) of 315 GABHS stains isolated from patients receiving AZM were resistant to this compound. On Day 14 pretreatment GABHS were eradicated from 78 (57.8%) of the 135 children receiving the AZM 10 mg regimen, 131 (94.2%) of the 139 receiving AZM 20 mg and 123 (84.2%) of the 146 taking penicillin. One month after the outset of treatment, bacteriologic relapses were observed in 40.5% (n = 30) of the children receiving AZM 10 mg, 14.8% (n = 18) of children taking AZM 20 mg and 13.2% (n = 15) of those treated with penicillin V. AZM 20 mg/kg/day was statistically superior to AZM 10 mg/kg/day microbiologically on Day 14 (P = 0.0001) and Day 30 (P = 0.0001) and clinically on Day 14 (P = 0.0035). AZM 20 mg/kg/day was statistically equivalent both microbiologically and clinically to standard therapy with penicillin V at all endpoints. The incidence of treatment-related adverse events was similar in the two azithromycin groups [AZM 10 mg, 31 of 169 (18.3%); AZM 20 mg, 37 of 164 (23%)] but significantly higher than those observed in the penicillin V group [5 of 166 (3%); P < 0.0001]. Most treatment-related adverse events were gastrointestinal and of mild-to-moderate severity. Fourteen patients withdrew from the trial because of adverse events (1 in the penicillin V group, 7 in the AZM 10 mg group and 6 in the AZM 20 mg group).

CONCLUSION

This is the first study to demonstrate a daily dose-dependent difference in microbiologic efficacy of a regimen; 3-day AZM 20 mg/kg/day is a more effective regimen than 3-day AZM 10 mg/kg/day for pediatric GABHS tonsillopharyngitis.

Pharmacokinetics of azithromycin in foals after i.v. and oral dose and disposition into phagocytes

The properties of azithromycin suggest that it may be an alternative to erythromycin for treatment of Rhodococcus equi pneumonia in foals. To investigate this possibility, the disposition of azithromycin in plasma, polymorphonuclear leukocytes (PMN), and alveolar cells was examined after a single administration in foals. Azithromycin suspension was administered orally (p.o.) at a dose of 10 mg/kg to five healthy 2-3-month-old foals. Two weeks later, azithromycin for injection was administered by intravenous (i.v.) infusion at a dose of 5 mg/kg to the same foals. Plasma samples were collected after p.o. and i.v. administration. Peripheral blood PMN and bronchoalveolar lavage fluid and alveolar cells were collected after p.o. administration. Azithromycin concentrations were determined by reverse-phase high-performance liquid chromatography (HPLC) with coulometric electrochemical detection. Azithromycin p.o. absorption was variable with a mean systemic availability of 39% (+/-20%). The plasma half-life was 16 and 18.3 h after i.v. and p.o. administration, respectively. Azithromycin had a very large volume of distribution (V(d)) of 11.6 L/kg [V(d(ss))] and 12.4 L/kg [V(d(area))]. The large V(d) can be attributed to high tissue and intracellular concentrations, exhibited by the high concentration of azithromycin in PMN and alveolar cells. The PMN half-life was 49.2 h. Dosage of 10 mg/kg of azithromycin p.o. once daily for foals with R. equi pneumonia is recommended for further study.

The macrolides

Erythromycin, which was introduced over 50 years ago, was the first macrolide to be used clinically. "New" macrolides, for the treatment of patients with various infectious diseases, were not clinically introduced until 40 years later. The pharmacokinetic and adverse events profile of erythromycin initially limited its use to an alternative agent for patients with allergy to beta-lactam agents. However, the emergence of atypical and/or new pathogens and the ongoing escalation of acquired antimicrobial resistance has impacted on the empirical and organism directed therapy of infectious diseases. Azithromycin and clarithromycin were developed by enhancing the basic macrolide structure. Some of the basic features associated with these new agents include a pharmacokinetic profiles that allow once or twice daily dosing with a much lower incidence of side effects and a substantially broader spectrum of activity which includes some Gram-negative bacilli, atypical pathogens and new, unconventional or uncommon pathogens. Clinical trial data has supported the use of "new" macrolides in a wide range of clinical indications, however, some specific indications are currently restricted to treatment with either azithromycin or clarithromycin. Macrolide resistance is a class effect and depending on the mechanism will confer either low or high level resistance. While resistance is problematic, it does not always result in clinical failure. The macrolides are a valuable class of antimicrobial agent and play an important role in the management of infectious diseases.

Low efficacy of an ultra-short term, once-daily dose triple therapy with omeprazole, azithromycin, and secnidazole for Helicobacter pylori eradication in peptic ulcer

PURPOSE

To determine the eradication rate of an ultra-short treatment schedule for Helicobacter pylori infection in a population with peptic ulcers, using omeprazole, secnidazole, and azithromycin in a once-daily dose for 3 days.

METHODS

Thirty patients with peptic ulcer diagnosed by upper endoscopy and for Helicobacter pylori infection by rapid urease test and histologic examination received omeprazole 40 mg, secnidazole 1000 mg, and azithromycin 500 mg, administered once daily for 3 days. A follow-up exam was performed 12 weeks after the end of the treatment. Patients who were negative for Helicobacter pylori infection by rapid urease test and histologic examination were considered cured.

RESULTS

Patients were predominantly female, and the mean age was 50 years. Duodenal peptic ulcer was found in 73% of the patients. Eradication was achieved in 9 of the 28 (32%) patients as determined from the follow-up endoscopic exam. The eradication rate by intention to treat was 30%. Side effects were present in 3% of the patients, and compliance to treatment was total.

CONCLUSIONS

In spite of the low rate of side effects and good compliance, the eradication index was low. A possible drawback of this therapy is that it reduces the efficacy of macrolide and nitroimidazole compounds in subsequent treatments.

Review of macrolides and ketolides: focus on respiratory tract infections

The first macrolide, erythromycin A, demonstrated broad-spectrum antimicrobial activity and was used primarily for respiratory and skin and soft tissue infections. Newer 14-, 15- and 16-membered ring macrolides such as clarithromycin and the azalide, azithromycin, have been developed to address the limitations of erythromycin. The main structural component of the macrolides is a large lactone ring that varies in size from 12 to 16 atoms. A new group of 14-membered macrolides known as the ketolides have recently been developed which have a 3-keto in place of the L-cladinose moiety. Macrolides reversibly bind to the 23S rRNA and thus, inhibit protein synthesis by blocking elongation. The ketolides have also been reported to bind to 23S rRNA and their mechanism of action is similar to that of macrolides. Macrolide resistance mechanisms include target site alteration, alteration in antibiotic transport and modification of the antibiotic. The macrolides and ketolides exhibit good activity against gram-positive aerobes and some gram-negative aerobes. Ketolides have excellent activity versus macrolide-resistant Streptococcus spp. Including mefA and ermB producing Streptococcus pneumoniae. The newer macrolides, such as azithromycin and clarithromycin, and the ketolides exhibit greater activity against Haemophilus influenzae than erythromycin. The bioavailability of macrolides ranges from 25 to 85%, with corresponding serum concentrations ranging from 0.4 to 12 mg/L and area under the concentration-time curves from 3 to 115 mg/L x h. Half-lives range from short for erythromycin to medium for clarithromycin, roxithromycin and ketolides, to very long for dirithromycin and azithromycin. All of these agents display large volumes of distribution with excellent uptake into respiratory tissues and fluids relative to serum. The majority of the agents are hepatically metabolised and excretion in the urine is limited, with the exception of clarithromycin. Clinical trials involving the macrolides are available for various respiratory infections. In general, macrolides are the preferred treatment for community-acquired pneumonia and alternative treatment for other respiratory infections. These agents are frequently used in patients with penicillin allergies. The macrolides are well-tolerated agents. Macrolides are divided into 3 groups for likely occurrence of drug-drug interactions: group 1 (e.g. erythromycin) are frequently involved, group 2 (e.g. clarithromycin, roxithromycin) are less commonly involved, whereas drug interactions have not been described for group 3 (e.g. azithromycin, dirithromycin). Few pharmacoeconomic studies involving macrolides are presently available. The ketolides are being developed in an attempt to address the increasingly prevalent problems of macrolide-resistant and multiresistant organisms.

In vitro activities of antibiotics against Plasmodium falciparum are inhibited by iron

The in vitro activities of cyclines (tetracycline, doxycycline, minocycline, oxytetracycline, and rolitetracycline), macrolides (erythromycin, spiramycin, roxithromycin, and lincomycin), quinolones (norfloxacin and ofloxacin), rifampin, thiamphenicol, tobramycin, metronidazole, vancomycin, phosphomycin, and cephalosporins (cephalexin, cefaclor, cefamandole, cefuroxime, ceftriazone, cefotaxime, and cefoxitin) were evaluated on Plasmodium falciparum clones, using an isotopic, micro-drug susceptibility test. Only tetracyclines, macrolides, quinolones, and rifampin demonstrated in vitro activity against P. falciparum, which increased after a prolonged exposure (96 or 144 h). In the presence of iron (FeCl(3)), only the activities of tetracyclines and norfloxacin were decreased. Their in vitro activity against intraerythrocytic stages of multidrug-resistant P. falciparum and their efficacy in vivo favor the use of antibiotics as antimalarial drugs. However, due to their slow antimalarial action and to the fact that they act better after prolonged contact, they probably need to be administered in conjunction with a rapidly acting antimalarial drug, such as a short course of chloroquine or quinine.

Inoculation of two genotypes of Hemobartonella felis (California and Ohio variants) to induce infection in cats and the response to treatment with azithromycin

OBJECTIVES

To describe clinical and laboratory findings associated with cats experimentally infected by inoculation with the 2 recognized genotypes of Hemobartonella felis (small variant, Hfsm; large variant, Hflg) and to determine the response of cats to treatment with azithromycin.

ANIMALS

18 young adult domestic shorthair cats of both sexes.

PROCEDURES

Cats were inoculated with H felis and monitored weekly, using CBC counts and a polymerase chain reaction (PCR) designed to detect both genetic variants of H felis. Beginning 26 days after inoculation, 11 cats were administered azithromycin (15 mg/kg of body weight, PO, q 12 h, for 7 days).

RESULTS

Inoculation resulted in coinfection with Hflg and Hfsm, and both variants were detected by PCR. Clinical abnormalities and anemia were most severe in Hflg- and dual-infected cats. Results of PCR and CBC were positive for H felis in 112/112 (100%) and 42/112 (37.5%), respectively, samples collected after inoculation. Administration of azithromycin had little effect on clinical variables, including anemia. All cats, regardless of treatment with azithromycin, had positive results for the PCR at the end of the study period.

CONCLUSIONS AND CLINICAL RELEVANCE

In these cats, Hflg was more pathogenic than Hfsm, and coinfection with both variants was detected. Results of the PCR were superior to results of CBC for detecting infection with H felis. Azithromycin administered at the dose and duration reported here was not efficacious for the treatment of cats with hemobartonellosis.

Community-acquired pneumonia in the elderly: a practical guide to treatment

The incidence of community-acquired pneumonia (CAP), an infectious disease, sharply increases among the elderly and the main risk factor for CAP in this age group is chronic comorbidity. The use of the term CAP in the elderly population should be reserved for pneumonia acquired outside of the nursing home setting, since nursing home-acquired pneumonia differs from CAP in terms of its aetiology and clinical manifestations. The main aetiology for CAP is Streptococcus pneumoniae, but atypical pathogens also play an important role as causative agents. The clinical presentations of CAP in the elderly can be different from those in younger patients, and therefore it is important to be aware of and familiar with these differences to avoid unnecessary delays in reaching the correct diagnosis. Imaging is essential to diagnose CAP and to assess its severity. Clinical and laboratory indices can be used to identify elderly patients with CAP who are at low risk for mortality and who can be treated as outpatients. The decision not to hospitalise elderly patients with CAP is contingent on a good clinical condition and the existence of home support systems. The aetiology of CAP cannot be determined on the basis of clinical manifestations, imaging or routine laboratory test results, and the initial antibiotic therapy for elderly patients with CAP should be empirical, based on accepted guidelines. In the light of developments in recent years, elderly patients with CAP, except those who are severely ill, can be treated empirically with once-daily antibiotic monotherapy in the initial phase, using a third-generation fluoroquinolone preparation, such as sparfloxacin, levofloxacin or moxifloxacin, or a new macrolide such as clarithromycin, azithromycin or dirithromycin. In addition to antibiotic therapy, it is critically important to identify and treat the physiological disturbances that accompany CAP as well as decompensation of chronic comorbid conditions. As soon as the patient's condition permits, oral antibiotic therapy should replace intravenous therapy and early discharge from the hospital should be considered. Since influenza and pneumococcus immunisation can reduce morbidity and mortality from CAP, it is important to implement regular immunisation programmes in the primary care setting.

The newer macrolides: azithromycin and clarithromycin

Azithromycin and clarithromycin are two relatively new macrolide antimicrobial agents. Although azithromycin and clarithromycin are structural analogues of erythromycin, they offer distinct advantages in comparison. This article reviews the pharmacokinetics, antimicrobial activity, clinical use, and adverse affects of these antimicrobial agents.

Past use of erythromycin, tetracycline, or doxycycline is not associated with risk of first myocardial infarction

A population-based case-control study of patients enrolled at Group Health Cooperative of Puget Sound was conducted to evaluate whether past use of antibiotics active against Chlamydia pneumoniae is associated with a decrease in the risk of first myocardial infarction (MI). Cases with incident fatal and nonfatal MI from mid-1986 through 1995 (n=1796) were compared with randomly sampled controls frequency-matched to cases for age, sex, and year (n=4882). Use of erythromycin, tetracycline, or doxycycline during the previous 5 years was not associated with an alteration in the risk of first MI. In an adjusted logistic regression model, the odds ratios and 95% confidence intervals for categories of cumulative duration of therapy with any of the three agents combined for 0, 1-14, 15-28, and >/=29 days were 1.0 (reference), 0.93 (0.81-1.07), 0.99 (0.81-1.20), and 1.03 (0.84-1.26), respectively. These results suggest little or no association between past use of erythromycin or tetracycline antibiotics and the risk of first MI among this population.

Azithromycin versus pivampicillin in the treatment of acute exacerbations of chronic bronchitis: a single-blind, double-dummy, multicentre study

This single-blind, double-dummy, multicentre study compared oral azithromycin, administered as tablets, 500 mg once daily for 3 days, versus oral pivampicillin, 700 mg twice daily for 10 days, in adults with acute exacerbations of chronic bronchitis (not needing parenteral antibiotic therapy, hospitalization or oxygen support). Clinical success (cure + improvement) rates were similar for both groups at the end of treatment (day 10; azithromycin, 124 of 133 [93%]; pivampicillin, 79 of 92 [86%]) and at follow-up (day 52; 98 of 126 [78%] versus 66 of 81 [81%]). The treatments produced similar levels of pathogen eradication at the end of treatment (49 of 54 [91%] versus 32 of 37 [86%]). Azithromycin-treated patients had significantly reduced chest discomfort at the end of treatment, and a trend towards improved lung function. The two groups were similar with respect to improvements in other clinical symptoms and patient well-being, and to the incidences of adverse events and treatment discontinuations. This oral azithromycin regime is an effective treatment for acute exacerbations of chronic bronchitis, similar in efficacy to the longer pivampicillin regime and may offer superior patient compliance.

Azithromycin: indications for the future?

The global challenge of optimally treating bacterial infections is continuously evolving. Azithromycin, the first azalide antibiotic, presents pharmacokinetics and pharmacodynamics that allow for a simple dosing regimen with minimal side effects. Current azithromycin uses include a variety of community-acquired respiratory tract, skin and soft tissue, and sexually transmitted disease infections. Azithromycin has also demonstrated substantial activity against atypical organisms such as Mycobacterium avium complex (MAC) and Chlamydia trachomatis. Due to a never-ending need for new antibiotic therapies, several other potential indications for azithromycin are being researched. This article will present various current research associated with azithromycin's potential use for malaria, trachoma, coronary artery disease (CAD), Pseudomonas aeruginosa infections, erythema migrans, short-term therapy for respiratory infections, typhoid, cryptosporidiosis, pelvic inflammatory disease, acne, Mediterranean spotted fever and MAC. As bacterial and parasite resistance patterns fluctuate globally, azithromycin may be an alternative therapy for the previously mentioned indications, which will also enhance patient compliance and therefore effectively eradicate infection worldwide.

Azithromycin: antimalarial profile against blood- and sporozoite-induced infections in mice and monkeys

The spectrum of antimalarial activity of the new macrolide antibiotic azithromycin was evaluated against blood- and sporozoite-induced infections with a chloroquine-resistant strain of Plasmodium yoelii nigeriensis (N-67) in Swiss mice and with simian parasite Plasmodium cynomolgi B in rhesus monkeys. Against experimental rodent malaria, a 70 mg/kg/day dose showed curative blood-schizontocidal activity in a four-dose regimen administered orally from day 0 to day 3 or from day 2 to day 5 to mice harboring established infection. The curative response was also obtained with a 40 mg/kg/day dose administered in an extended seven-dose (days 0-6) regimen. Azithromycin was also effective in the causal prophylactic test, since a 50 mg/kg dose from day -1 to day +2 protected mice against P. y. nigeriensis (N-67) sporozoite challenge. In comparison, erythromycin did not show either of the above activities up to a 405 mg/kg/day dose in identical regimens. Comparison of the ED(90) values showed that azithromycin was 31-fold more effective than erythromycin as a blood schizontocide. In the simian model, trophozoite-induced infections of P. cynomolgi B were cured with 25 mg/kg/day azithromycin administered for 7 days. In the causal prophylactic test, the prepatent period was significantly extended in monkeys challenged with P. cynomolgi B sporozoites, presumably because of the growth inhibition of preerythrocytic schizonts in hepatocytes. Azithromycin did not exhibit any hypnozoitocidal (dormant exoerythrocytic stages) activity at 25 mg/kg/day in a seven-dose regimen.

Once-daily therapy for H. pylori infection: a randomized comparison of four regimens

OBJECTIVE

We sought to determine the efficacy and tolerability of novel, once-daily therapies in the treatment of Helicobacter pylori infection.

METHODS

One hundred sixty subjects with H. pylori infection documented by endoscopic biopsy or serology plus 13C-urea breath test were randomly assigned to omeprazole 80 mg q.d. and metronidazole extended-release formulation 750 mg q.d. for 10 days (OM); OM plus amoxicillin 1.5 g q.d. for 10 days (OMAm); OM plus azithromycin 500 mg q.d. for 7 days (OMAz); or OM plus clarithromycin 1 g q.d. for 10 days (OMCI). A repeat breath test was done 6 wk after the completion of therapy. Subjects were considered compliant if they took > or = 80% of each study medication as prescribed.

RESULTS

Intent-to-treat eradication rates were OM = 8% (95% confidence interval [CI], 2-20%), OMAm = 35% (95% CI, 21-52%), OMAz = 65% (95% CI, 48-79%), and OMCI = 78% (95% CI, 62-89%). Lack of compliance was seen in 5% of subjects given OM, 8% given OMAm, 3% given OMAz, and 15% given OMCI.

CONCLUSIONS

This pilot study demonstrated that once-daily triple therapy with high-dose omeprazole, metronidazole extended-release formulation, and clarithromycin achieved an eradication rate approaching 80%. Further study may permit development of optimal once-daily dosing and enhance eradication rates.

Intravenous azithromycin

OBJECTIVE

To review the pharmacology, microbiology, chemistry, pharmacokinetics, efficacy, safety, tolerability, dosage, administration, and economic issues of intravenous azithromycin.

DATA SOURCES

A MEDLINE search from 1978 to May 1998 of the English-language literature and an extensive review of journals and meeting abstracts was conducted. Due to the lack of published literature concerning the efficacy, safety, and pharmacokinetics of the intravenous formulation of azithromycin, the manufacturer was also contacted and requested to supply information concerning intravenous azithromycin.

DATA EXTRACTION

In vitro and preclinical studies were included, as well as data from Phase II and III clinical trials. Efficacy, pharmacokinetic, safety, and tolerability data were also supplemented with information from the manufacturer, due to the lack of published reports.

DATA SYNTHESIS

Azithromycin, an azalide subclass of the macrolide antibiotics, is now available as an intravenous formulation. The intravenous form is approved for the treatment of community-acquired pneumonia caused by Chlamydia pneumoniae, Haemophilus influenzae. Legionella pneumophila, Moraxella catarrhalis, Mycoplasma pneumoniae, Staphylococcus aureus (methicillin-sensitive), and Streptococcus pneumoniae, and for the treatment of pelvic inflammatory disease caused by Chlamydia trachomatis, Neisseria gonorrhoeae, and Mycoplasma hominis in situations in which intravenous therapy is required. Its spectrum of activity, unique pharmacokinetics, and high and sustained tissue penetration allow for once-daily dosing with monotherapy in many cases. Clinical and bacteriologic response rates as well as the adverse event profile have been similar to or better than comparative agents.

CONCLUSIONS

Azithromycin offers advantages over other agents due to its unique pharmacokinetics, high and sustained tissue penetration, and spectrum of activity. This allows for monotherapy and once-daily intravenous dosing for mild-to-moderate community-acquired pneumonia or pelvic inflammatory disease in many instances. Future research should focus on total duration of antibiotic therapy and the need, or lack thereof, for extensive oral antibiotic follow-up.

Lack of association between first myocardial infarction and past use of erythromycin, tetracycline, or doxycycline

To evaluate the association of prior treatment with antibiotics active against Chlamydia pneumoniae with the risk for incident myocardial infarction, we conducted a population-based case-control study. We found that use of erythromycin, tetracycline, or doxycycline during the previous 5 years was not associated with risk for first myocardial infarction. These results suggest little or no association between the use of these antibiotics and the risk for first myocardial infarction in the primary prevention setting.

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.

Advances in the macrolides and quinolones

The widespread, frequent clinical use of the macrolides and quinolones has led to resistance in several species. With the prevailing increase of resistance, new developmental compounds with improved spectra, pharmacokinetics, and reduced adverse effects are required, coupled with logical use of the current armamentarium.

A comparison of the efficacy, tolerability and safety of azithromycin and co-amoxiclav in the treatment of sinusitis in adults

The efficacy, tolerability and safety of azithromycin and co-amoxiclav in the treatment of non-severe acute maxillary/ethmoidal sinusitis were compared in a randomized, open clinical trial in 254 adult patients. The predominant pathogens were Streptococcus pneumoniae and Haemophilus influenzae (83 patients). Azithromycin was administered orally to 165 patients at a single daily dose of 500 mg for 3 days, and co-amoxiclav (4:1) to 89 patients, at a dose of 500 mg three times daily for 10 days. The overall clinical response rates were 87.5% for azithromycin and 83.7% for co-amoxiclav at follow-up (day 21-28). Microbiological responses to both drugs were good, with only five patients in each group having a persistent infection after treatment. Both drugs were well tolerated and produced similar incidences of adverse events, which were mostly gastrointestinal. Azithromycin was as effective, and as well tolerated as co-amoxiclav, and its shorter simpler dosing regime may offer advantages in compliance and cost.

Pharmacokinetics of drugs used in critically ill adults

Critically ill patients exhibit a range of organ dysfunctions and often require treatment with a variety of drugs including sedatives, analgesics, neuromuscular blockers, antimicrobials, inotropes and gastric acid suppressants. Understanding how organ dysfunction can alter the pharmacokinetics of drugs is a vital aspect of therapy in this patient group. Many drugs will need to be given intravenously because of gastrointestinal failure. For those occasions on which the oral route is possible, bioavailability may be altered by hypomotility, changes in gastrointestinal pH and enteral feeding. Hepatic and renal dysfunction are the primary determinants of drug clearance, and hence of steady-state drug concentrations, and of efficacy and toxicity in the individual patient. Oxidative metabolism is the main clearance mechanism for many drugs and there is increasing recognition of the importance of decreased activity of the hepatic cytochrome P450 system in critically ill patients. Renal failure is equally important with both filtration and secretion clearance mechanisms being required for the removal of parent drugs and their active metabolites. Changes in the steady-state volume of distribution are often secondary to renal failure and may lower the effective drug concentrations in the body. Failure of the central nervous system, muscle, the endothelial system and endocrine system may also affect the pharmacokinetics of specific drugs. Time-dependency of alterations in pharmacokinetic parameters is well documented for some drugs. Understanding the underlying pathophysiology in the critically ill and applying pharmacokinetic principles in selection of drug and dose regimen is, therefore, crucial to optimising the pharmacodynamic response and outcome.

An open, multicentre, comparative study of the efficacy and safety of azithromycin and co-amoxiclav in the treatment of upper and lower respiratory tract infections in children. The Paediatric Azithromycin Study Group

An open prospective, multicentre, comparative, randomized (2:1) study was conducted in 481 children diagnosed as having mild-to-moderate lower respiratory tract infections. The efficacy and safety of azithromycin suspension (10 mg/kg), dosed orally once daily for 3 days, was compared with that of co-amoxiclav (10 mg/kg in a 4:1 ratio), dosed orally three times daily for 5-10 days. The proportion of evaluable patients (n = 472) showing a cure or improvement was significantly higher in the azithromycin group (96.8%) than in the co-amoxiclav group (91%, P = 0.0199). There were six relapses in both groups, giving an overall response rate of 95% for azithromycin versus 87.1% for co-amoxiclav (P = 0.0025). Adverse events were reported in 10% of the patients treated with azithromycin, and 11.3% of co-amoxiclav patients. Reported and counted compliance was significantly better in the azithromycin group. A 3-day regimen of azithromycin was as effective and as safe as a 5-10 day regimen of co-amoxiclav in the treatment of respiratory tract infections in children, and compliance was improved.

Requirements for intracellular accumulation and release of clarithromycin and azithromycin by human phagocytes

Determination of clarithromycin (CL) and azithromycin (AZ) uptake by human polymorphonuclear leukocytes (PMNs), monocytes and alveolar macrophages showed that AZ achieved higher levels than CL. The uptake kinetics of AZ were time-dependent over an 18 h period, while those of CL were similar to erythromycin (ER) kinetics, with a maximum level of incorporation being obtained after a 60 min incubation. The accumulation of both drugs was influenced by extracellular antibiotic-concentrations, PMN viability, extracellular calcium, physiological environmental temperature and pH. The uptake was not modified by inhibitors of cell metabolism or activators of cell membranes. After removal of extracellular antibiotic, the release of AZ from PMNs was very slow: nearly 50% of the drug remained cell-associated after 24 h incubation. The efflux of this derivative was significantly enhanced when drug-loaded PMNs were stimulated by phorbol-myristate acetate (PMA). The kinetics of CL release indicated that this macrolide behaved like ER. Nevertheless, about 10% of the initial cell-associated antibiotic showed a prolonged retention. On the whole, these data suggest that diffusion through cell membranes and trapping into acidic compartments of PMNs are important events in CL and AZ uptake.

Comparison of azithromycin and co-amoxiclav in the treatment of acute tracheobronchitis and acute infectious exacerbations of chronic bronchitis in adults. Azithromycin Study Group

Azithromycin, a broad-spectrum azalide, and co-amoxiclav were compared in a randomized, multicentre, open-label trial in 759 patients treated for acute tracheobronchitis (n = 620) or acute infectious exacerbations of chronic bronchitis (n = 139). Patients were randomized (2:1) to a 3-day regimen of two azithromycin 250 mg capsules once daily or a 5-10-day regimen of co-amoxiclav, one 625 mg tablet three times daily. Azithromycin produced a significantly higher cure rate (70.6% versus 61.1%) than co-amoxiclav (P = 0.011) and there were fewer failures (7.8% versus 13.6%) and relapses in the azithromycin-treated group, giving a higher overall response rate for azithromycin (89.7% versus 80.2%, P = 0.0003). With azithromycin, compliance was better than with co-amoxiclav and there was a significantly shorter time to improvement or cure. A higher incidence of adverse events, mostly gastrointestinal, was reported by patients taking co-amoxiclav (21.3% versus 14%, P = 0.0097), causing more patients in this group to discontinue therapy (7% versus 1.2%, P = 0.00004).