Outpatient parenteral antibiotic therapy. Management of serious infections. Part I: Medical, socioeconomic, and legal issues. Selecting the antibiotic

Delivering Antibacterials to the Lungs

An important determinant of clinical outcome of a lower respiratory tract infection may be sterilization of the infected lung, which is also dependent on sustained antibacterial concentrations achieved in the lung. For this reason, recently there has been increased interest in measuring the concentration of antimicrobial agents at different potential sites of infection in the lung. Levels of antibacterials are now measured in bronchial mucosa, epithelial lining fluid (ELF) and alveolar macrophages, as well as in sputum. Penicillins and cephalosporins reach only marginal concentrations in bronchial secretions, whereas fluoroquinolones and macrolides have been shown to achieve high concentrations. The extent of penetration of different antibacterials into the bronchial mucosa is relatively high. This is also true for beta-lactams, although their tissue concentrations never reach blood concentrations. Antibacterials penetrate less into the ELF than into the bronchial mucosa, but fluoroquinolones appear to concentrate more into alveolar lavage than into bronchial mucosa. Pulmonary pharmacokinetics is a very useful tool for describing how drugs behave in the human lung, but it does not promote an understanding of the pharmacological effects of a drug. More important, instead, is the correlation between pulmonary disposition of the drug and its minimum inhibitory concentration (MIC) values for the infectious agent. The addition of bacteriological characteristics to in vivo pharmacokinetic studies has triggered a 'pharmacodynamic approach'. Pharmacodynamic parameters integrate the microbiological activity and pharmacokinetics of an anti-infective drug by focusing on its biological effects, particularly growth inhibition and killing of pathogens. Drugs that penetrate well and remain for long periods at the pulmonary site of infection often induce therapeutic responses greater than expected on the basis of in vitro data. However, although the determination of antibacterial concentrations at the site of infection in the lung has been suggested to be important in predicting the therapeutic efficacy of antimicrobial treatment during bacterial infections of the lower respiratory tract, some studies have demonstrated that pulmonary bacterial clearance is correlated more closely to concentrations in the serum than to those in the lung homogenates, probably because they better reflect antibacterial concentration in the interstitial fluid.

A model for home infusion therapy initiation and maintenance

Many factors impact the success of home infusion therapy. A model has been designed to incorporate all of the factors that need to be considered when setting up a home infusion program. The primary factors included in the model are patient, nursing, medical, caregiver, equipment, environment, medication, and legal issues. Each of the factors are subdivided into relevant points to be included in the patient's discharge management plan. Using the model will help nurses make a comprehensive patient assessment, plan patient and caregiver education, and assist patients in completing their course of infusion therapy.

Parenteral antibiotic therapy in the treatment of lower respiratory tract infections. Strategies to minimize the development of antibiotic resistance

Antibiotic use is often imputed for increases in the prevalence of infections due to antibiotic-resistant bacteria. Resistance depends on the variety of genotypes in the large bacterial population and also on the selective pressures that are produced along the antibiotic concentration gradients in the body. In effect, at certain selective concentrations the antibiotic eliminates the susceptible majority, leaving a selected remainder intact. Therefore, the choice of antibiotics for the treatment of lower respiratory tract infections should take into consideration not only their effectiveness but also the pharmacokinetics of each agent and its delivery schedule. In fact, the potential therapeutic efficacy of an antibiotic depends not only on its spectrum of action, but also on the concentration it reaches at the site of infection. Most infections occur in the tissues of the body rather than in the blood and that it is accepted that appropriate antibiotic therapy requires the maintenance of significant concentrations of antibiotics at the site of infection in the lung long enough to eliminate the invading pathogen. Thus, the development of dosing schedules for most antimicrobials has been based on the postulate that drug levels need to be above the minimal inhibitory concentration (MIC) at this site for most or all the dosing interval. The selection of antimicrobial resistance appears to be strongly associated with suboptimal antimicrobial exposure, defined as an AUIC(0-24)/MIC ratio of less than 100O125. Antimicrobial regimens that do not achieve these values cannot prevent the selective pressure that leads to overgrowth of resistant bacterial subpopulations. It has been suggested that resistance can be avoided with attention to dosing, since dosing which provides an AUIC(0-24)/MIC ratio of at least 100 appears to reduce the rate of the development of bacterial resistance. Unfortunately, very different serum or lung concentration profiles can result in the same AUIC(0-24)/MIC. High doses administered sufficiently may often completely prevent any possibility of attaining a selective concentration. Alternatively, an antibiotic which has good bactericidal potency and maintains tissue and/or serum concentrations greater than the MIC or, better, minimal bactericidal concentration (MBC) throughout the dosing interval is equally effective in minimizing the development of antibiotic resistance.

Comparative study of dirithromycin and azithromycin in the treatment of acute bacterial exacerbations of chronic bronchitis

We compared the clinical and microbiological efficacy of dirithromycin with that of azithromycin in outpatients with acute bacterial exacerbations of chronic bronchitis who could be graded into stage III according to Ball's system of stratification. A total of 80 patients was studied. Of these, 40 were treated with dirithromycin as a once-daily dose of 500 mg for 5 days, and 40 with azithromycin as a once-daily dose of 500 mg for 3 days. At post-therapy, treatment success (cure or improvement) was achieved in 36 out of 40 (90%) patients receiving dirithromycin compared with 37 out of 40 (92.5%) in the azithromycin group. At the late post-therapy visit, 34 out of 36 (94.4%) dirithromycin-treated patients were cured as were 33 of 37 (89.2%) azithromycin-treated patients. A small proportion of patients treated with dirithromycin (10%) or with azithromycin (12.5%) suffered mild side effects. Gastrointestinal disorders, including abdominal cramps, nausea, or diarrhea, were common adverse effects. The main pathogens isolated before treatment were Streptococcus pneumoniae, Haemophilus influenzae, and Moraxella catarrhalis. Eradication rates at the end of treatment were 90% (36 out of 40) for the dirithromycin group and 92.5% (37 out of 40) for the azithromycin group. Persistence of H. influenzae isolates was found in 3 out of 11 (27.3%) patients treated with dirithromycin and in 2 out of 9 (22.2%) who had received azithromycin. At the late post-therapy visit, eradication occurred in 34 out of 36 (94.4%) strains in the dirithromycin group and in 33 out of 37 (89.2%) in the azithromycin group. We conclude that dirithromycin and azithromycin appear to be equally effective in the treatment of acute bacterial exacerbations of chronic bronchitis.

Intravenous antimicrobial therapy in the community: underused, inadequately resourced, or irrelevant to health care in Britain?

The NHS Executive is keen to promote "hospital at home" services in Britain, as part of its philosophy of keeping more care in the community and also to relieve the increasing demand for hospital beds. One such service is the provision of intravenous antimicrobial therapy in the community. Yet, compared with the United States, where home or outpatient intravenous antimicrobial therapy programmes are well developed, experience in Britain and Europe is limited, reflecting a difference in cultural attitudes and healthcare structures between the two continents. Only a few units in Britain currently run home intravenous antimicrobial therapy programmes, and several issues need to be addressed if more treatment is to be provided outside hospital. These include an assessment of the need for community intravenous antibiotic treatment and which patient groups many benefit. The main motive for community intravenous treatment should be better patient care and not simply a reduction in healthcare costs. At present the pace of change is being set by a few clinical enthusiasts and by commercial organisations, whereas the NHS deserves a more organised strategy for purchasing treatment with intravenous antibiotics in the community.

Antibiotic selection factors and description of a hospital-based outpatient antibiotic therapy program in the USA

A variety of pharmacodynamic, pharmacokinetic and drug stability factors can influence the choice of drug, the dosing regimen and the method of drug administration for out-patient parenteral antibiotic therapy (OPAT). Beta-lactam antibiotics exhibit little if any concentration-dependent killing and produce short-term or no persistent effects with most bacterial pathogens. Optimal dosing regimens for these agents should provide serum levels that continually exceed the minimal inhibitory concentration (MIC) of the pathogen. Beta-lactam agents with long half-lives (greater than 2 hours) can provide these levels with intermittent dosing once or twice daily. Beta-lactam agents with shorter half-lives can be administered by programmable pumps or by continuous infusion providing the drug is sufficiently stable to degradation in solution. Imipenem and ampicillin are examples of drugs with short half-lives that are unstable in solution and must be dosed intermittently. Intramuscular administration slows absorption and can also prolong the length of time during which serum levels exceed the MIC of infecting bacteria. Aminoglycosides and fluoroquinolones, on the other hand, exhibit concentration-dependent killing and produce prolonged persistent effects. Optimal dosage regimens of these drugs should maximize serum levels. Once-daily dosing regimens for the aminoglycosides meet this goal and also appear to reduce drug-induced nephrotoxicity. Application of these principles to drug selection and administration in a hospital-based OPAT program has provided efficacious therapy and a low incidence of adverse reactions in an elderly population distributed over a wide geographic area.

Antibiotic kinetics and dynamics for the clinician

In recent decades considerable data have been acquired concerning the complex interactions of the organism-antimicrobial-host triad. Using the current understanding of drug disposition in the body, pharmacokinetics, and in vitro microbiologic activity, optimal dosing strategies can be derived to maximize clinical efficacy and minimize potential toxicities. This article discusses pharmacokinetics, pharmadynamics, and the application of this principle in clinical practice.

Beta-lactam antibiotics: is continuous infusion the preferred method of administration?

OBJECTIVE

To examine the pharmacodynamic properties of the beta-lactam class of antibiotics and the rationale for their continuous infusion (CI), and to explore reasons that this mode of administration has not replaced intermittent infusion as the standard of practice.

DATA SOURCES

A Medline search of the English-language literature evaluating CI administration of beta-lactam antibiotics was conducted. Bibliographic searches of these articles also were performed.

STUDY SELECTION

Because there were few human trials, all available trials were considered for review. A cross section of clinical trials, animal studies, and in vitro studies examining the impact of the route of antibiotic administration was selected for each pharmacodynamic variable addressed.

DATA SYNTHESIS

The support for CI as the preferred method of beta-lactam administration comes primarily from in vitro and animal data. Most beta-lactam antibiotics do not demonstrate concentration-dependent killing and have an appreciable postantibiotic effect only against gram-positive cocci. Their efficacy appears to be optimized by maintaining suprainhibitory concentrations throughout the dosing interval. Therefore, CI of beta-lactams could potentially enhance the efficacy of treatment or allow less drug to be used on a daily basis. This has yet to be demonstrated convincingly in human clinical trials. Comparative trials need to continue to explore the impact of the method of administration on patient outcomes such as duration and cost of therapy, as well as morbidity and mortality.

CONCLUSIONS

Results of many animal and in vitro studies suggest that CI may be the optimal method of beta-lactam administration. Clinical trials need to further document the impact of the method of beta-lactam administration on the incidence of adverse effects, emergence of bacterial resistance, and patient outcome. Pharmacodynamic studies defining target beta-lactam concentrations, the practicality of CI in patients requiring multiple intravenous fluids and medications, and the pertinence of this issue when beta-lactam antibiotics are used as sole agents or in combination with other antimicrobials require further exploration.