An open study to compare the pharmacokinetics, safety and tolerability of a multiple-dose regimen of azithromycin in young and elderly volunteers

Pharmacotherapy options and drug development in managing periprosthetic joint infections in the elderly

INTRODUCTION

Prosthetic joint infections are an increasingly important problem among patients undergoing arthroplasty procedures, and are associated with significant morbidity, reduced quality of life, substantial healthcare costs, and even mortality. Arthroplasties are performed with increasing frequency in elderly patients, who present specific problems.

AREAS COVERED

Surgical therapy is clearly influenced by the clinical status of the patient, which in some case can contraindicate surgery. Antibiotic selection is also affected by comorbidities and underlying diseases, which in some cases reduce therapeutic options. The authors review this together with the changes in pharmacokinetics and pharmacodynamics in the elderly population and the prospects for future research on prevention and treatment.

EXPERT OPINION

The management of PJI in the elderly makes multidisciplinary teams even more mandatory than in other patients, because the complexity of these patients. A frequent scenario is that in which surgery is contraindicated with long-term suppressive treatment as the only available option. Treating physicians must consider the presence of multiple comorbidities, interactions with other treatments and secondary effects when choosing antibiotic treatment. An in-depth knowledge of the alterations in pharmacokinetics and pharmacodynamics in elderly patients is key for a proper treatment selection.

Antimicrobial Pharmacokinetics and Pharmacodynamics in Older Adults

Antimicrobial use in older adults requires working knowledge of the pharmacokinetics and pharmacodynamics of these drugs, and the alterations known to occur with these models as patients age. A summary of pharmacokinetic principles relevant to antimicrobials and an overview of published medical literature describing pharmacokinetic changes known to correlate with age are presented. Pharmacodynamic models that apply to antibacterial agents are reviewed, as are likely effects of aging on these models. The understanding of how older adults respond in terms of efficacy and toxicity is increasing but limited. Further research into the effects of aging on the actions of antimicrobials in the elderly is needed.

A novel ceftazidime/avibactam, rifabutin, tedizolid and moxifloxacin (CARTM) regimen for pulmonary Mycobacterium avium disease

Objectives

To compare the efficacy of ceftazidime/avibactam plus tedizolid-based combination regimens with the standard therapy of azithromycin, ethambutol and rifabutin for the treatment of pulmonary Mycobacterium avium complex (MAC) disease.

Methods

We mimicked the human pulmonary concentration-time profiles of ceftazidime/avibactam and tedizolid in combination, ceftazidime/avibactam, rifabutin, tedizolid and moxifloxacin (CARTM), and the standard regimen and examined microbial kill in triplicate hollow-fibre system model of intracellular pulmonary MAC (HFS-MAC) units. The tedizolid and moxifloxacin doses used were non-optimized; the tedizolid dose was that associated with bacteriostasis. Drugs were administered daily for 28 days. Each HFS-MAC was sampled in the central and peripheral compartment to ascertain that the intended drug exposures had been achieved. The peripheral compartments were sampled at regular intervals over the 28 days to quantify the burden of MAC.

Results

MAC-infected macrophages in the HFS-MAC achieved multi-fold higher intracellular versus extracellular concentrations of rifabutin, moxifloxacin, ceftazidime/avibactam. The non-optimized ceftazidime/avibactam plus tedizolid dual therapy held the bacterial burden at the same level as day 0 (stasis) throughout the 28 days. The standard therapy reduced the bacterial load 2 log10 cfu/mL below stasis on day 14 but started failing after that. The CARTM regimen achieved 3.2 log10 cfu/mL kill below stasis on day 21, but had started to fail by day 28.

Conclusions

The CARTM regimen promises to have kill rates better than standard therapy. Experiments to identify exposures of each of the four drugs associated with optimal effect in the CARTM combination are needed in order to design a short-course chemotherapy regimen.

The Role of Macrolides in Chronic Rhinosinusitis (CRSsNP and CRSwNP)

PURPOSE OF REVIEW

We assess the literature on the pharmacokinetics, indications, important considerations, and effectiveness of long-term, low-dose macrolide antibiotics in chronic rhinosinusitis (CRS).

RECENT FINDINGS

The key to effective implementation of macrolide therapy in CRS is appropriate patient selection. Macrolides have demonstrated the most benefit in Th1-mediated non-eosinophilic CRS when used for durations of at least 3 months. Macrolide antibiotics have demonstrated great benefit when used for their anti-inflammatory or immunomodulatory properties, which include the blockage of pro-inflammatory cytokines, such as interleukin (IL)-8 and tumor necrosis factor-α (TNF-α). They have been used in CRS patients not responding to traditional corticosteroid-based treatment regimens, but appear to be most effective specifically in Th1-mediated non-eosinophilic CRS in long durations and low doses. Further research is needed to better identify characteristics known to correlate with macrolide response so early directed therapy can be implemented.

Azithromycin: mechanisms of action and their relevance for clinical applications

Azithromycin is a macrolide antibiotic which inhibits bacterial protein synthesis, quorum-sensing and reduces the formation of biofilm. Accumulating effectively in cells, particularly phagocytes, it is delivered in high concentrations to sites of infection, as reflected in rapid plasma clearance and extensive tissue distribution. Azithromycin is indicated for respiratory, urogenital, dermal and other bacterial infections, and exerts immunomodulatory effects in chronic inflammatory disorders, including diffuse panbronchiolitis, post-transplant bronchiolitis and rosacea. Modulation of host responses facilitates its long-term therapeutic benefit in cystic fibrosis, non-cystic fibrosis bronchiectasis, exacerbations of chronic obstructive pulmonary disease (COPD) and non-eosinophilic asthma. Initial, stimulatory effects of azithromycin on immune and epithelial cells, involving interactions with phospholipids and Erk1/2, are followed by later modulation of transcription factors AP-1, NFκB, inflammatory cytokine and mucin release. Delayed inhibitory effects on cell function and high lysosomal accumulation accompany disruption of protein and intracellular lipid transport, regulation of surface receptor expression, of macrophage phenotype and autophagy. These later changes underlie many immunomodulatory effects of azithromycin, contributing to resolution of acute infections and reduction of exacerbations in chronic airway diseases. A sub-group of post-transplant bronchiolitis patients appears to be sensitive to azithromycin, as may be patients with severe sepsis. Other promising indications include chronic prostatitis and periodontitis, but weak activity in malaria is unlikely to prove crucial. Long-term administration of azithromycin must be balanced against the potential for increased bacterial resistance. Azithromycin has a very good record of safety, but recent reports indicate rare cases of cardiac torsades des pointes in patients at risk.

Pharmacokinetics of EDP-420 after multiple oral doses in healthy adult volunteers and in a bioequivalence study

EDP-420 (also known as EP-013420, or S-013420) is a first-in-class bridged bicyclolide currently in clinical development for the treatment of respiratory tract infections (RTI) and has previously shown favorable pharmacokinetic (PK) and safety profiles after the administration of single oral doses of a suspension to healthy volunteers. Here we report its PK profile after the administration of multiple oral doses of a suspension to healthy adults. Bioequivalence between suspension and capsule formulations, as well as the effect of food, is also reported. The most important PK features of EDP-420 observed in these clinical studies are its long half-life of 17 to 18 h and its high systemic exposure, which support once-daily dosing and treatment durations potentially shorter than those of most other macrolide antibiotics. EDP-420 is readily absorbed following oral administration in both suspension and capsule formulations. In the multiple-oral-dose study, steady state was achieved on day 1 by using a loading dose of 400 mg/day, followed by 2 days of 200 mg/day. A high-fat meal had no effect on the bioavailability of EDP-420 administered in a capsule formulation. EDP-420 was well tolerated, with no serious or severe adverse events reported, and no subject was discontinued from the study due to an adverse event. Based on its human PK and safety profiles, together with its in vitro/in vivo activities against common respiratory pathogens, EDP-420 warrants further development, including trials for clinical efficacy in the treatment of RTI.

Pharmacokinetics of EDP-420 after ascending single oral doses in healthy adult volunteers

EDP-420 (EP-013420, S-013420) is a first-in-class bicyclolide (bridged bicyclic macrolide) currently in clinical development for the treatment of respiratory tract infections. It has good preclinical pharmacokinetic properties across multiple species and potent in vitro and in vivo activity against respiratory tract infection pathogens, including Haemophilus influenzae, atypical organisms (e.g., Chlamydia pneumoniae, Mycoplasma pneumoniae, and Legionella pneumophila), and multidrug-resistant streptococci. The safety, tolerability, and pharmacokinetics of an orally administered EDP-420 suspension in 40 healthy adult subjects were assessed in a randomized, double-blind, placebo-controlled, ascending single-dose study. Eligible subjects were sequentially randomized into one of five study groups (i.e., 100-, 200-, 400-, 800-, or 1,200-mg dosing groups) consisting of eight subjects (six active and two placebo) each. EDP-420 was well tolerated. There were no serious adverse events reported, nor were there any dose-limiting clinical or laboratory adverse events reported. EDP-420 was rapidly absorbed after a single oral dose. The mean plasma terminal half-life ranged from 15.6 to 20.1 h with low clearance. At the 400-mg dose, the area under the curve was 14.4 microg x h/ml, which well exceeded the required area under the concentration-time curve to cover common respiratory tract infection pathogens based on preclinical pharmacokinetic/pharmacodynamic modeling. The long half-life and high systemic exposure of EDP-420 support once-daily dosing and may allow for shorter treatment durations compared to other macrolide antibiotics. Based on its human pharmacokinetic profiles, taken together with its in vitro/in vivo activity against common respiratory pathogens, EDP-420 warrants efficacy trials for the treatment of respiratory tract infections.

Pharmacokinetics in older persons

BACKGROUND

Physiologic changes and disease-related alterations in organ function occur with aging. These changes can affect drug pharmacokinetics in older persons.

OBJECTIVE

This article reviews age-related changes in pharmacokinetics and their clinical relevance.

METHODS

A PubMed search was conducted using the terms elderly and pharmacokinetics. Other reviews were also included for literature searching. The review includes literature in particular from 1990 through April 2004. Some articles from before 1990 were included to help illustrate principles of age-related pharmacokinetics.

RESULTS

There are minor changes in drug absorption with aging. The effect of aging on small-bowel transporter systems is not yet fully established. Bioavailability of highly extracted drugs often is increased with age. Transdermal absorption may be delayed, especially in the case of water-soluble compounds. Fat-soluble drugs may distribute more widely and water-soluble drugs less extensively in older persons. Hepatic drug metabolism shows wide interindividual variation, and in many cases, there is an age-related decline in elimination of metabolized drugs, particularly those eliminated by the cytochrome enzyme system. Any decrement in cytochrome enzyme metabolism appears nonselective. Synthetic conjugation metabolism is less affected by age. Pseudocapillarization of the sinusoidal endothelium in the liver, restricting oxygen diffusion, and the decline in liver size and liver blood flow may influence age-related changes in rate of hepatic metabolism. Frailty, physiological stress, and illness are important predictors of drug metabolism in older individuals. Inhibition of drug metabolism is not altered with aging, but induction is reduced in a minority of studies. Renal drug elimination typically declines with age, commensurate with the fall in creatinine clearance. Renal tubular organic acid transport may decline with age, while the function of the organic base transporter is preserved but may be less responsive to stimulation.

CONCLUSION

Changes in pharmacokinetics occur due to age-related physiologic perturbations. These changes contribute to altered dose requirements in older persons, particularly in the case of drugs eliminated by the kidney. Interindividual variation, disease, frailty, and stress may overshadow age-related changes.

In vitro activity and pharmacodynamics of azithromycin and clarithromycin against Streptococcus pneumoniae based on serum and intrapulmonary pharmacokinetics

BACKGROUND

Multidrug-resistant strains of Streptococcus pneumoniae are increasingly common worldwide, but the clinical significance of their resistance to the macrolide antibiotics is controversial. Applying pharmacokinetic and pharmacodynamic principles can assist in the selection of appropriate antimicrobial therapy.

OBJECTIVES

The purpose of this study was to determine the in vitro activity of penicillin, azithromycin, clarithromycin, and clindamycin against clinical isolates of S. pneumoniae and to evaluate the pharmacodynamics of azithromycin and clarithromycin based on serum and epithelial lining fluid (ELF) concentrations.

METHODS

The minimum inhibitory concentrations (MICs) of penicillin, azithromycin, clarithromycin, and clindamycin were determined for 307 isolates of S. pneumoniae using broth microdilution. Using serum and ELF concentrations after standard dosing, we calculated the proportion of isolates against which it would be possible to obtain a ratio of azithromycin area under the curve to MIC > or =25 and clarithromycin concentrations that exceeded the MIC for > or =40% of the dosing interval.

RESULTS

Overall, 19.5%, 25.4%, 25.1%, and 7.2% of the 307 pneumococcal isolates were resistant to penicillin, azithromycin, clarithromycin, and clindamycin, respectively. However, 71.7% of penicillin-resistant strains were also resistant to azithromycin and clarithromycin. Based on serum concentrations, clarithromycin achieved its pharmacodynamic target in 76.9% of isolates, compared with 59.9% for azithromycin. Based on ELF concentrations, clarithromycin achieved its pharmacodynamic target in 93.5% of isolates, compared with 74.6% for azithromycin. Based on ELF concentrations, clarithromycin achieved its pharmacodynamic target in 86.7% of penicillin-resistant isolates, compared with 28.3% for azithromycin.

CONCLUSIONS

On the basis of serum and ELF concentrations, clarithromycin achieved pharmacodynamic targets against a greater proportion of S. pneumoniae isolates than did azithromycin. Clinical studies are needed to determine the efficacy of these agents against pneumococci that demonstrate in vitro resistance using current susceptibility breakpoints.

The macrolides: erythromycin, clarithromycin, and azithromycin

In addition to erythromycin, macrolides now available in the United States include azithromycin and clarithromycin. These two new macrolides are more chemically stable and better tolerated than erythromycin, and they have a broader antimicrobial spectrum than erythromycin against Mycobacterium avium complex (MAC), Haemophilus influenzae, nontuberculous mycobacteria, and Chlamydia trachomatis. All three macrolides have excellent activity against the atypical respiratory pathogens (C. pneumoniae and Mycoplasma species) and the Legionella species. Azithromycin and clarithromycin have pharmacokinetics that allow shorter dosing schedules because of prolonged tissue levels. Both azithromycin and clarithromycin are active agents for MAC prophylaxis in patients with late-stage acquired immunodeficiency syndrome (AIDS), although azithromycin may be the preferable agent because of fewer drug-drug interactions. Clarithromycin is the most active MAC antimicrobial agent and should be part of any drug regimen for treating active MAC disease in patients with or without AIDS. Although both azithromycin and clarithromycin are well tolerated by children, azithromycin has the advantage of shorter treatment regimens and improved tolerance, potentially improving compliance in the treatment of respiratory tract and skin or soft tissue infections. Intravenously administered azithromycin has been approved for treatment of adults with mild to moderate community-acquired pneumonia or pelvic inflammatory diseases. An area of concern is the increasing macrolide resistance that is being reported with some of the common pathogens, particularly Streptococcus pneumoniae, group A streptococci, and H. influenzae. The emergence of macrolide resistance with these common pathogens may limit the clinical usefulness of this class of antimicrobial agents in the future.

Safety, toleration, and pharmacokinetics of intravenous azithromycin

To date, the clinical pharmacology of large intravenous doses of azithromycin has not been described. In the present study, single 2-h intravenous infusions of 1, 2, and 4 g of azithromycin were administered to three parallel groups (in each group, six received active drug and two received placebo) of healthy male subjects. Toleration (assessed by scores of subject-administered visual analog scale tests spanning 0 [good] to 10 [poor]), safety, pharmacokinetics, and serum motilin levels were monitored for up to 240 h after the start of each intravenous infusion. Mean nausea scores of 0.0, 0.0, 1.0, and 0.5 and abdominal cramping scores of 0.0, 0.0, 0.4, and 0.4 for 12-h periods after doses of 0, 1, 2, and 4 g of azithromycin, respectively, suggested that azithromycin was well tolerated. Because of the standardized 1-mg/ml infusates, all subjects in the 4-g dosing group complained of an urgent need to urinate. There were no consistent trends in endogenous motilin levels throughout the study. The maximum concentration of azithromycin in serum (10 micrograms/ml after a 4-g dose) and the area under the concentration-time curve (82 micrograms.h/ml after a 4-g dose) were dose related. The mean pharmacokinetic parameters were an elimination half-life of 69 h, total systemic clearance of 10 ml/min/kg, and a volume of distribution at steady state of 33.3 liters/kg. The pharmacokinetic results suggest that the long half-life of azithromycin is due to extensive uptake and slow release of the drug from tissues rather than an inability to clear the drug. Single intravenous doses of up to 4 g of azithromycin in healthy subjects are generally well tolerated, and quantifiable concentrations may persist in serum for 10 days or more.

Comparative pharmacokinetics of macrolide antibiotics and concentrations achieved in polymorphonuclear leukocytes and saliva

OBJECTIVES: The pharmacokinetics of macrolide antibiotics --- erythromycin (ER), clarithromycin (CL), roxithromycin (RO), azithromycin (AZ), dirithromycin (DI) and the concentrations achieved in polymorphonuclear neutrophils (PMNs) and saliva were investigated. METHODS: In a four-way crossover trial, 10 healthy volunteers received 1000 mg ER twice a day, 500 mg CL twice a day, 150 mg RO twice a day and 500 mg AZ every day over a period of 3 days. In a second trial, 10 healthy volunteers received 500 mg DI every day over a period of 5 days. Concentrations of these antibiotics were measured in serum, urine, saliva and PMNs by high-performance liquid chromatography (HPLC) on days 1 and 3 in the first trial and on days 1 and 5 in the second trial. RESULTS: We found considerable differences in the pharmacokinetics, not only in serum, but also in PMNs and saliva. All substances except RO exhibited higher concentrations in PMNs than in serum, indicating excellent intraphagocytic distribution. In contrast, concentrations in saliva were lower than those measured in serum, with the exception of AZ. ER is characterized by low serum concentrations and moderate concentrations in saliva and PMNs. CL reached considerable concentrations in serum, saliva and PMNs. RO achieved the highest serum levels, but concentrations in saliva and in PMNs were below the detection limit. In contrast, AZ and DI yielded the lowest serum concentrations and the highest saliva and PMN concentrations. CONCLUSIONS: Our data emphasize the importance of tissue distribution, in addition to serum kinetics, in evaluating the pharmacokinetic profiles of antibiotics.

Pharmacokinetics of azithromycin in pediatric patients with acute otitis media

The objective of our study was to characterize the pharmacokinetics of azithromycin after the oral administration of multiple doses in suspension to children with acute otitis media. Thirteen children (ranging in age from 7.5 months to 5 years) received a single oral dose of 10 mg of azithromycin per kg of body weight on day 1 followed by single daily doses of 5 mg/kg on days 2 to 5. Each child fasted overnight before receiving the final dose on day 5. Multiple blood samples were collected after the last dose. Concentrations of azithromycin in serum were measured by a specific high-performance liquid chromatography-mass spectrometry method. The means and standard deviations for the maximum concentration of azithromycin in serum, the time to maximum concentration of azithromycin in serum, the area under the concentration-time curve (from 0 to 24 h), and the elimination half-life were 224 +/- 120 ng/ml, 1.8 +/- 0.4 h, 1,841 +/- 651 ng.h/ml, and 31.6 +/- 6.6 h, respectively. Concentrations in serum (means +/- standard deviations) at 0 h (predose) and at 24, 48, and 72 h after the final dose were 51 +/- 26, 47 +/- 21, 27 +/- 17, and 17 +/- 13 ng/ml, respectively. Thus, the once-daily administration of azithromycin resulted in sustained systemic exposure to the drug. The drug dosage regimen used in this study should lead to tissue drug concentrations exceeding the MICs for common pathogens.

An open-label, noncomparative study to evaluate the efficacy, safety, and tolerability of azithromycin in the treatment of patients with acute sinusitis

The efficacy, safety, and tolerability of a 5-day, once-daily course of azithromycin were assessed in patients with acute sinusitis. Patients received two 250-mg capsules of azithromycin on day 1 and one 250-mg capsule on days 2 through 5. Of 102 clinically assessable patients, 27 (26.5%) were cured and 69 (67.6%) were improved on days 5 to 7. At days 12 to 16, 88 (86.3%) had a favorable clinical response. A total of 64 patients experienced adverse events; in all but two patients, adverse events were of mild or moderate severity. Thus azithromycin given once daily for 5 days was an effective treatment for patients with acute sinusitis.

In vitro and in vivo activities of azithromycin, a new azalide antibiotic, against chlamydia

The in vitro and in vivo activities of azithromycin against chlamydia were investigated. The MIC of azithromycin for five standard strains of different species of chlamydia and six wild-type strains of Chlamydia pneumoniae was 0.125 microgram/ml, which was superior to that of erythromycin but inferior to those of clarithromycin and minocycline. However, the therapeutic effect of a 7-day course of azithromycin at a dose of 10 mg/kg of body weight administered orally once daily to mice with experimental Chlamydia psittaci pneumonia was excellent, with a 100% survival rate at 14 days after infection, which was the same as that for treatment with minocycline administered at 10 mg/kg twice daily; all erythromycin treated animals died within 10 days. When treatment was discontinued 3 days after the infection, the survival rate for mice treated with azithromycin was 90% and that for mice administered minocycline was 30%. These results suggest that azithromycin may be useful in the treatment of respiratory infections caused by intracellular pathogens, including chlamydia because of its excellent accumulation within host cells.

Azithromycin prophylaxis against a chloroquine-resistant strain of Plasmodium falciparum

Azithromycin has antimalarial activity and favourable pharmacokinetic properties for a prophylactic antimalarial agent. We investigated the ability of azithromycin to prevent malaria in volunteers infected with a chloroquine-resistant strain of Plasmodium falciparum. 4 volunteers received oral azithromycin 500 mg followed by 250 mg daily for 7 further days. Subjects were infected on the third day of azithromycin. 3 subjects were protected compared with none of 15 controls. The volunteer not protected by azithromycin had unquantifiable plasma levels of azithromycin, probably because of poor absorption. Azithromycin could be a promising prophylactic agent for P falciparum malaria.

Ocular pharmacokinetics of orally administered azithromycin in rabbits

Azithromycin was orally administered to Dutch-belted rabbits following extracapsular lens extraction in one eye. At various times the animals were sacrificed, and serum and ocular tissues were obtained for drug level determination by HPLC-EC. Following a single dose, peak levels of drug in ocular tissues were measured within 8 hours (cornea > 0.5 micrograms/g [15mg/kg]; > 1.5 micrograms/g [3Omg/kg]). Highest levels were obtained in iris and ciliary body ( > 15 micrograms). Measurable tissue levels persisted for at least 120 hours. Trough levels increased proportionately during drug multiple dose administration. Five days following five daily 15mg/kg doses, corneal levels exceeded 0.5 micrograms/g, and iris and ciliary levels were higher than 15 micrograms/g. Aqueous humor and serum levels were equivalent. Vitreous humor levels, though higher than aqueous humor, were consistently < 1 microgram/ml. Extracapsular cataract extraction did not significantly affect drug uptake.

Azithromycin clinical pharmacokinetics

Azalide antibiotics, of which azithromycin is the first demonstrated, have different pharmacokinetics from other antibiotics currently used. The bioavailability of the drug is approximately 37%. Extensive and rapid distribution from serum into the intracellular compartments is followed by rapid distribution to the tissues. Tissue concentrations exceed serum concentrations by up to 100-fold following a single azithromycin 500mg dose. Concentration of the drug within phagocytes aids in its ability to combat infections. High concentrations of azithromycin are found in the tonsil, lung, prostate, lymph nodes and liver, with only small concentrations found in fat and muscle. A 500mg dose on day 1, followed by 250mg daily on days 2 to 5, has been demonstrated to maintain azithromycin concentrations at sites of infection and continues to be effective for several days after administration has ceased. The pharmacokinetics of azithromycin make it a drug with diverse therapeutic applications.

Pharmacokinetics of azithromycin in pediatric patients after oral administration of multiple doses of suspension

Azithromycin is an azalide antibiotic. On the basis of data in adults, azithromycin appears to have a greater distribution into tissues, a longer elimination half-life, and a lower incidence of adverse effects than the macrolide antibiotic erythromycin. However, little about the pharmacokinetics of azithromycin in children is known. The objective of our study was to characterize the pharmacokinetics of azithromycin after oral administration of multiple doses of suspension to children with streptococcal pharyngitis. Fourteen children (6 to 15 years of age) received a single oral dose of 10 mg of azithromycin per kg of body weight on day 1 followed by single daily doses of 5 mg/kg on days 2 to 5. Each child fasted overnight before receiving the final dose on day 5. Blood samples were collected at 0, 0.5, 1, 2, 4, 6, 8, 12, 24, 48, and 72 h after this last dose. Concentrations of azithromycin in serum were measured by a specific high-performance liquid chromatography-mass spectrometry method. The mean +/- standard deviation for maximum concentration of drug in serum, time to maximum concentration of drug in serum, and area under the curve (0 to 24 h) were 383 +/- 142 ng/ml, 2.4 +/- 1.1 h, and 3,109 +/- 1,033 ng.h/ml, respectively. Concentrations in serum at 0 h (predose) and at 24, 48, and 72 h after the final dose were 67 +/- 31, 64 +/- 24, 41 +/- 17, and 29 +/- 14 ng/ml, respectively. Thus, once-daily administration of azithromycin resulted in sustained systemic exposure to the drug.

Azithromycin. A review of its antimicrobial activity, pharmacokinetic properties and clinical efficacy

Azithromycin is an acid stable orally administered macrolide antimicrobial drug, structurally related to erythromycin, with a similar spectrum of antimicrobial activity. Azithromycin is marginally less active than erythromycin in vitro against Gram-positive organisms, although this is of doubtful clinical significance as susceptibility concentrations fall within the range of achievable tissue azithromycin concentrations. In contrast, azithromycin appears to be more active than erythromycin against many Gram-negative pathogens and several other pathogens, notably Haemophilus influenzae, H. parainfluenzae, Moraxella catarrhalis, Neisseria gonorrhoeae, Urea-plasma urealyticum and Borrelia burgdorferi. Like erythromycin and other macrolides, the activity of azithromycin is unaffected by the production of beta-lactamase. However, erythromycin-resistant organisms are also resistant to azithromycin. Following oral administration, serum concentrations of azithromycin are lower than those of erythromycin, but this reflects the rapid and extensive movement of the drug from the circulation into intracellular compartments resulting in tissue concentrations exceeding those commonly seen with erythromycin. Azithromycin is subsequently slowly released, reflecting its long terminal phase elimination half-life relative to that of erythromycin. These factors allow for a single dose or single daily dose regimen in most infections, with the potential for increased compliance among outpatients where a more frequent antimicrobial regimen might traditionally be indicated. The potential disadvantage of low azithromycin serum concentrations, however, is that breakthrough bacteraemia may occur in patients who are severely ill; nevertheless, animal studies suggest that tissue concentrations of azithromycin are more important than those in serum when treating respiratory and other infections. The clinical efficacy of azithromycin has been confirmed in the treatment of infections of the lower and upper respiratory tracts (the latter including paediatric patients), skin and soft tissues (again including paediatric patients), in uncomplicated urethritis/cervicitis associated with N. gonorrhoeae, Chlamydia trachomatis or U. urealyticum and in the treatment of early Lyme disease. Azithromycin was as effective as erythromycin and other commonly used drugs including clarithromycin, beta-lactams (penicillins and cephalosporins), and quinolone and tetracycline antibiotics in some of the above infections. Some patients with acute exacerbations of chronic bronchitis due to H. influenzae may be refractory to therapy with azithromycin (as is the case with erythromycin) indicating the need for physician vigilance, although it should be noted that azithromycin is of equivalent efficacy to amoxicillin in the treatment of such patients. In the therapy of urethritis/cervicitis associated with C. trachomatis, N. gonorrhoea or U. urealyticum, a single dose azithromycin regimen offers a distinct advantage over currently available pharmacological options, while providing effective therapy.(ABSTRACT TRUNCATED AT 400 WORDS)