Single or multiple daily doses of aminoglycosides: a meta-analysis

Aminoglycoside-associated nephrotoxicity in the elderly

OBJECTIVE

To determine whether there was an increased incidence of nephrotoxicity in elderly patients (> or =65 y) prescribed single-dose (SD) versus multiple-dose (MD) aminoglycosides and whether aminoglycoside-induced nephrotoxicity was associated with length of therapy and other risk factors.

METHODS

A prospective, observational audit at a university teaching hospital was conducted. Physician prescribing was used to stratify subjects according to dosing regimen: MD (n = 60) or SD (n = 26). Nephrotoxicity was defined as an increase in the serum creatinine level of 0.5 mg/dL sustained over 2 days.

RESULTS

Eighty-six patients were included; 9.3% developed nephrotoxicity, of whom 62.5% received SD therapy. The incidence of nephrotoxicity did not differ between regimens (p = 0.051). There was an increased length of therapy in those who developed nephrotoxicity (mean +/- SD 6.1 +/- 6.2 vs. 3.7 +/- 2.8 d; p = 0.044). Additionally, patients who developed nephrotoxicity had an increased length of hospitalization (20.3 +/- 16.1 vs. 8.4 +/- 5.4 d; p < 0.001). Nephrotoxicity correlated with a diagnosis of diabetes mellitus (OR 15.1; 95% CI 1.11 to 205), concomitant angiotensin-converting enzyme (ACE) inhibitor therapy (OR 28.0; 95% CI 2.15 to 365), and SD therapy (OR 20.7; 95% CI 1.45 to 297).

CONCLUSIONS

Our overall incidence of nephrotoxicity is consistent with that reported in the literature. A diagnosis of diabetes mellitus, concomitant use of ACE inhibitors, and SD regimens were risk factors for the development of nephrotoxicity. An adequately powered, randomized trial is needed to assess whether a difference in the incidence of nephrotoxicity exists between SD and MD therapy in the elderly.

Clinical issues surrounding once-daily aminoglycoside dosing in children

Aminoglycoside antibiotics are first-line treatment for many infectious diseases in the pediatric population and are effective in adults. The traditional dosing interval in children is every 8-12 hours. Studies in adults reported equivalent efficacy and equal or less toxicity with once-daily regimens. Despite many studies in the adult population, this approach has yet to become standard practice in most pediatric hospitals. Reasons for lack of acceptance of this strategy in children include rapid aminoglycoside clearance, unknown duration of postantibiotic effect, safety concerns, and limited clinical and efficacy data.

Efficacy and tolerability of extended-interval aminoglycoside administration in pediatric patients

Aminoglycosides are commonly used to treat serious Gram-negative infections in pediatric patients. An effort to improve the efficacy and tolerability of this antibiotic class has led to evaluation of extended-interval aminoglycoside administration (EIAA). EIAA is designed to achieve higher peak plasma aminoglycoside concentrations, with relatively undetectable trough concentrations, when compared with conventional aminoglycoside administration (CAA), and is therefore expected to be markedly effective and to reduce drug accumulation and prevent nephrotoxicity and ototoxicity. Clinical trials evaluating EIAA in neonates included patients with suspected Gram-negative infections requiring short courses of aminoglycoside therapy. Consequently, comparative efficacy of EIAA versus CAA could not be assessed. In addition, ototoxicity was often not assessed, and nephrotoxicity was virtually undetectable. Similarly, trials evaluating EIAA versus CAA in infants and children have not demonstrated a difference in outcomes. The use of EIAA in children with febrile neutropenia has been evaluated primarily with amikacin. The incidences of nephrotoxicity and ototoxicity were low, and were similar between EIAA and CAA. No deaths were reported in any of these studies; however, this could be related to the inclusion of patients with undocumented bacteremia. Further investigation of EIAA is necessary in patients with documented bacteremia, since plasma aminoglycoside concentrations were undetectable for most of the dosage interval in children with febrile neutropenia who were treated once daily. Overall, clinical studies suggest that EIAA has similar efficacy to, and no higher risk of toxicity than, CAA in neonates, infants, and children. A few evaluations have also demonstrated that EIAA is cost-effective in neonates and in children with febrile neutropenia. Future studies evaluating the efficacy and tolerability of EIAA in pediatric patients with documented systemic infections should be prospective, randomized, controlled trials with sample sizes sufficient to detect differences between administration methods. Further evaluations should also address the optimal dosage and cost-effectiveness of EIAA in infants and children.

How should meta-regression analyses be undertaken and interpreted?

Appropriate methods for meta-regression applied to a set of clinical trials, and the limitations and pitfalls in interpretation, are insufficiently recognized. Here we summarize recent research focusing on these issues, and consider three published examples of meta-regression in the light of this work. One principal methodological issue is that meta-regression should be weighted to take account of both within-trial variances of treatment effects and the residual between-trial heterogeneity (that is, heterogeneity not explained by the covariates in the regression). This corresponds to random effects meta-regression. The associations derived from meta-regressions are observational, and have a weaker interpretation than the causal relationships derived from randomized comparisons. This applies particularly when averages of patient characteristics in each trial are used as covariates in the regression. Data dredging is the main pitfall in reaching reliable conclusions from meta-regression. It can only be avoided by prespecification of covariates that will be investigated as potential sources of heterogeneity. However, in practice this is not always easy to achieve. The examples considered in this paper show the tension between the scientific rationale for using meta-regression and the difficult interpretative problems to which such analyses are prone.

Comparison of once-daily versus twice-daily gentamicin dosing regimens in infants > or = 2500 g

OBJECTIVE

There is no uniformity in the current recommendations of dosing regimen of gentamicin for neonates. We conducted a prospective, randomized, controlled trial to compare a once-daily dosing regimen to the twice-daily dosing regimen for neonates > or = 2500 g during the first 7 days after birth.

STUDY DESIGN

Infants > or = 2500 g admitted to the Neonatal Intensive Care Unit and prescribed gentamicin for suspected bacterial infection were randomized to receive either 4 mg/kg every 24 hours, study group (n=20), or a standard regimen of 2.5 mg/kg every 12 hours, control group (n=21). Serum gentamicin concentrations (SGCs) were followed and gentamicin pharmacokinetics calculated on all infants.

RESULTS

Peak SGC 30 minutes after the first dose was 8.2+/-1.7 microg/ml in the study group, compared to 6.4+/-1.5 microg/ml in the control group (p=0.001). Ninety-five percent of study group infants, compared to 81% of the control group, had peak SGCs in therapeutic range after the first dose. Peak SGC at 48 hours (steady state) was 8.9+/-1.5 in the study group and 6.8+/-1.1 in the control group (p=0.0001). On further analysis, a significantly higher percentage of infants in the study group, compared to the control group, had peak SGCs in higher therapeutic ranges of 6 to 12 microg/ml as well as 8 to 12 microg/ml. None of the study infants, compared to six control infants, had trough SGCs > or = 2 microg/ml at steady state. Thus, none of the study group infants, versus six of the control group infants, needed a dosing adjustment at 48 hours (p=0.02, Fisher's exact test).

CONCLUSION

We found that 4 mg/kg gentamicin given every 24 hours achieved significantly higher peak SGCs and safe trough concentrations in all infants, compared to the twice-daily regimen of 2.5 mg/kg. We suggest that SGCs may not need to be followed in term infants prescribed a short course of this once-daily regimen for suspected early-onset sepsis if renal functions are normal.

[Efficacy and toxicity of aminoglycoside therapy in the elderly: combined effect of both once-daily regimen and therapeutic drug monitoring]

This study was aimed to compare with previous results (Grillot et al., 1994), the efficacy of amikacin adaptive optimal control in a geriatric hospital.

PATIENTS

During six months, 32 patients (aged of 82 +/- 8 years) were included versus 51 during two years (aged of 80 +/- 5). The mean age was not different between the two populations (NS, Student test). They received amikacin initial dosage of 17.7 +/- 5.1 mg/kg/d (vs 13.3 +/- 3.5 for the reference study) and maintenance dosage of 15.1 +/- 4.8 mg/kg/d (vs 11.8 +/- 5.1 for the reference study).

METHOD

Two efficacy outcomes (E1 and E2) and 1 toxicity outcome (T) were taken into account: E1 estimated the effect of adaptive control on maximal drug level, E2: overall recovery. Toxicity outcome was used: T the nephrotoxicity (increasing creatininémia over 44 mumol/l).

RESULTS

All the results are given versus the reference study. 57.6% versus 29.4% of adaptive strategy were once-a-day. E1: Chi square test show that initial dosage and maintenance dosage are greater our study than the previous one (p < 0.05: 78.8% versus 5.9% for initial dosage, 84.4% versus 13.8% for maintenance dosage). E2: 73.6% overall of recovery versus 77% (NS, Chi square test). T: 94% versus 85% (p < 0.05, Chi square test) of creatininemia variation are lower than 44 mumol/l. Duration of treatment is 9.8 +/- 4.8 versus 15 +/- 9 days (p < 0.5, Student test).

CONCLUSIONS

Once-a-day strategy in amikacin therapeutic regimen is no more efficient but decreases toxicity and duration treatment.

Extended interval aminoglycoside dosing: from concept to clinic

Extended-interval aminoglycoside dosing (EIAD), while a relatively recent concept in mainstream clinical practice, actually has its roots in the mid 1970s. Early trial and error approaches of manipulating the dosage regimen to avoid toxicity and improve efficacy have helped to characterize the pharmacodynamic properties of these drugs. The increasing successful use of EIAD and improved understanding of pharmacodynamics has helped this dosing regimen gain acceptance into routine clinical practice. A 1998 United States survey demonstrated that approximately 75% of hospitals have adopted EIAD into routine patient care. However, controversy still exists regarding some aspects of infrequent aminoglycoside administration, such as length of the drug-free interval and patient exclusion criteria. After more than 50 years of experience with the aminoglycosides we continue to learn how to most appropriately use these drugs.

Pharmacokinetic Analysis of Once-Daily Gentamicin in Immune-Compromised Adults with Normal Renal Function

Objective

To analyze and compare the pharmacokinetic parameters of a single daily dose (SDD) of gentamicin 5 mg/kg in adults with normal renal function who developed neutropenic fever during intensive non-nephrotoxic chemotherapy.

Methods

Ten patients received gentamicin in a 60-minute infusion and blood samples were drawn at 0, 0.5, 1, 2, 8, and 24 hours after the end of the infusion. Gentamicin concentrations were fitted to a noncompartment analysis (NCA) model and a 2-compartment open model for comparison.

Results

The mean ± SD gentamicin concentrations were: maximum concentration at 0.5 hours, 15.7 ± 3.4 mg/L; at 1 hour, 12.3 ± 2.3 mg/L; at 2 hours, 8.3 ± 2.5 mg/L; and at 8 hours, 1.7 ± 1 mg/L. The minimum concentration at 24 hours was 0.27 ± 0.36 mg/L. No statistical differences were established between the mean AUC (63 ± 8.5 and 54.2 ± 9.9 mg/L · h; p = 0.5) and gentamicin clearance (101.0 ± 13.3 and 160.6 ± 27.3 mL/min; p = 0.065). Statistical differences were demonstrated between the mean elimination rate constant (p < 0.001), half-life (p < 0.001), and volume of distribution (p < 0.001), measured by the NCA and the 2-compartment models.

Conclusions

Based on our findings, the NCA method for kinetic analysis of gentamicin prescribed in high SDD can be applied only for AUC and gentamicin clearance calculations.

Ototoxicity induced by gentamicin and furosemide

OBJECTIVE

To present a case of ototoxicity induced by furosemide and once-daily gentamicin therapy.

CASE SUMMARY

A 60-year-old white woman presented to the hospital with community-acquired pneumonia and urinary tract infection. The antibiotic regimen included gentamicin and, after 5 doses, the patient reported profound bilateral hearing loss. A Pure Tone Audiogram suggested moderate to moderately severe sensorineural hearing loss bilaterally. The only risk factors present included her age, elevated temperature, and the use of furosemide.

DISCUSSION

Several risk factors may predispose a patient to developing aminoglycoside ototoxicity: the 1555 chromosomal mutation, preexisting disorders of hearing and balance, hypovolemia, bacteremia, liver and renal dysfunction, and the simultaneous administration of other ototoxic medications. The cumulative dose and duration of aminoglycoside therapy are more important than serum concentrations. Administration of an aminoglycoside followed by furosemide may increase the risk of ototoxicity. The aminoglycoside interacts with the cell membranes in the inner ear, increasing their permeability. This theoretically allows the loop diuretic to penetrate into the cells in higher concentrations, causing more severe damage.

CONCLUSIONS

Auditory toxicity occurred after only 5 days of gentamicin therapy and 1 dose of furosemide. An aminoglycoside followed by furosemide may increase the risk for ototoxicity. Clinicians need to be aware of the synergistic potential of ototoxic medications.

Changing paradigms in the diagnosis and management of bronchiectasis

The face of bronchiectasis may have changed in recent years but individual cases continue to pose difficult challenges. As childhood infection becomes less of a problem, alternative causes of bronchiectasis are increasingly recognized which themselves offer new problems of diagnosis and management. Evolving concepts of pathogenesis suggest alternative strategies for treatment but as yet the evidence base on which to make firm decisions is lacking. Antibacterial regimens are not universally applicable and individualized protocols with parenteral, nebulized or continuous antibacterial therapy are increasingly used in the treatment of patients with bronchiectasis. Despite the theoretical appeal of using mucolytic or anti-inflammatory drugs their roles are still uncertain and have yet to be examined in adequate clinical trials. The factors determining disease progression are still poorly understood but in some patients worsening airflow obstruction heralds the onset of ventilatory failure. The management of the latter requires bronchodilators and controlled oxygen therapy, and strategies including non-invasive ventilation are increasingly an option. Changing indications for surgery are evident with fewer palliative resections but a developing role for transplantation.

Antibiotic regimens for endometritis after delivery

BACKGROUND

Post-partum endometritis, which is more common after cesarean section, occurs when vaginal organisms invade the endometrial cavity during labour and birth. Antibiotic treatment is warranted.

OBJECTIVES

The effect of different antibiotic regimens for the treatment of postpartum endometritis on failure of therapy and complications was systematically reviewed.

SEARCH STRATEGY

We searched the Cochrane Pregnancy and Childbirth Group's trials register and the Cochrane Controlled Trials Register. Date of last search: June 2001.

SELECTION CRITERIA

Randomised trials of different antibiotic regimens for postpartum endometritis, after cesarean section or vaginal birth, where outcomes of treatment failure or complications were reported were selected.

DATA COLLECTION AND ANALYSIS

Data were abstracted independently by the reviewers. Comparisons were made between different types of antibiotic regimen, based on type of antibiotic and duration and route of administration. Summary relative risks were calculated.

MAIN RESULTS

Forty-seven trials were included. Overall the studies were methodologically poor. In the intent-to-treat analysis, fifteen studies comparing clindamycin and an aminoglycoside with another regimen showed more treatment failures with another regimen (relative risk (RR) 1.32; 95% confidence interval (CI) 1.09-1.60). Failures of those regimens with poor activity against penicillin resistant anaerobic bacteria were more likely (RR 1.53; 95% CI 1.10-2.13). In four studies that compared continued oral antibiotic therapy after intravenous therapy, no differences were found in recurrent endometritis or other outcomes. There was no evidence of difference in incidence of allergic reactions. Cephalosporins were associated with less diarrhea.

REVIEWER'S CONCLUSIONS

The combination of gentamicin and clindamycin is appropriate for the treatment of endometritis. Regimens with activity against penicillin resistant anaerobic bacteria are better than those without. There is no evidence that any one regimen is associated with fewer side effects. Once uncomplicated endometritis has clinically improved with intravenous therapy, oral therapy is not needed.

A comparison of summary patient-level covariates in meta-regression with individual patient data meta-analysis

OBJECTIVES

To compare meta-analysis of summary study level data with the equivalent individual patient data (IPD) analysis when interest lies in identification of binary patient characteristics related to treatment efficacy.

DESIGN

A simulation study comparing meta-regression with IPD analyses of randomized controlled trials.

METHODS

Twenty-seven different meta-analysis situations were simulated with 1000 repetitions in each case. The following parameters were varied: (1) the treatment effect magnitude for different patient risk groups; (2) sample sizes of individual studies; and (3) number of studies. The meta-regression and IPD results were then compared for each situation.

RESULTS

The statistical power of meta-regression was dramatically and consistently lower than that of IPD analysis, with little agreement between the parameter estimates obtained from the two methods. Only in meta-analyses of large numbers of large trials, did meta-regression detect differential treatment effects between risk groups with any consistency.

CONCLUSIONS

Meta-analysis of summary data may be adequate when estimating a single pooled treatment effect or investigating study level characteristics. However, when interest lies in investigating whether patient characteristics are related to treatment, IPD analysis will generally be necessary to discover any such relationships. In these situations practitioners should try to obtain individual-level data.

Pharmacokinetic model for tobramycin in acinetobacter meningitis

OBJECTIVE

To report a case of acinetobacter meningitis treated with a once-daily intravenous dose of tobramycin and to propose a pharmacokinetic model for the drug disposition.

CASE SUMMARY

A 28-year-old man with chronic hydrocephalus was admitted with a diagnosis of intracranial hypertension. Acinetobacter spp. was detected in the cerebrospinal fluid (CSF); it was sensitive to tobramycin, ampicillin/sulbactam, and colistin. Based on the culture report, multiple daily-dose therapy with tobramycin was started. As the infectious symptoms remained, once-daily therapy was recommended; the optimal dose was calculated with nonlinear regression by least-squares analysis and a Bayesian method, using plasma and CSF samples. The infection was resolved, tobramycin therapy was discontinued, and the patient was discharged from the intensive care unit.

DISCUSSION

We use once-daily intravenous tobramycin therapy because, although the intrathecal administration of drugs is generally well tolerated, the presence of preservatives may be a source of central nervous system adverse effects. Pharmacokinetic parameters were calculated with plasma and CSF concentration values obtained during the first once-daily dose by using a compartment-effect model which allows fitting of simultaneous plasma and CSF concentrations. The prediction level was determined by the estimation of drug concentrations during the fourth once-daily dose. CSF concentrations of drug were enough to eradicate the clinical signs of infection.

CONCLUSIONS

Therapy using once-daily intravenous administration of tobramycin may be an adequate alternative for acinetobacter infections in neurosurgical patients when an intrathecal route is initially not recommended. The development of a compartment-effect model can be useful to predict drug concentrations.

Aminoglycoside nephrotoxicity: do time and frequency of administration matter?

Aminoglycosides remains the mainstay in the treatment of gram-negative infections despite their potential oto-and nephrotoxicity although alternatives with equal or better efficacy are available. Several approaches were investigated to decrease aminoglycosides nephrotoxicity. Among them, only the once-daily dosing of aminoglycosides has been brought to the clinic and physicians are now increasingly adopting this approach to reduce the toxicity of these agents. The incidence of aminoglycoside nephrotoxicity can be further reduced in view of the recent data on the circadian variations of their nephrotoxicity. In fact, it has been clearly demonstrated in both experimental animals and humans that the toxicity is maximal when the drug is injected during the rest period compared with the activity period. Thus, injecting aminoglycosides once-daily at the time of the lowest toxicity is actually the most interesting and clinically applicable approach to reduce aminoglycosides toxicity.

Pharmacodynamics of antiinfective therapy: taking what we know to the patient's bedside

Applied pharmacokinetics has long been a lifeline of clinical pharmacy services. National surveys during the past decade documented clinical pharmacy services and demonstrated that a substantial rate of growth occurred in clinical pharmacokinetic consultations and management of drug therapy protocols. Pharmacodynamic principles of antiinfective agents are rapidly becoming a new paradigm of clinical pharmacy services. beta-Lactams, aminoglycosides, and fluoroquinolones represent the three classes of antiinfective agents that have made the most progress toward the clinical applications of pharmacodynamics. Pharmacodynamic parameters are being used to select and compare agents within an antiinfective class (e.g., fluoroquinolones), make modifications in the dosage (e.g., extended-interval dosing of aminoglycosides) and/or mode of administration (e.g., continuous infusion of beta-lactams), develop in vivo breakpoint determinations, and assess the development of bacterial resistance. In addition, pharmacodynamic parameters have influenced the clinical drug development of new (e.g., linezolid) and older (amoxicillin-clavulanate, fluoroquinolones) antiinfective agents. Further investigations are needed to explore the clinician's use of validated prediction methods and patient-specific pharmacodynamic parameters at the bedside. By linking pharmacokinetic services with pharmacodynamic principles, the opportunity for continued progress toward our assessment and decisions for successful clinical outcomes is possible with old and new antiinfective agents.

Management of antimicrobial use in the intensive care unit

Indications for the use of antimicrobials in critically ill patients are similar to those for other hospitalised patients. However, the selection of agents depends on the particular characteristics of patients in the intensive care unit (ICU), the form of presentation of infection, the type of infection and the bacteriological features of the causative pathogens. The use of antimicrobials in patients admitted to medical-surgical ICUs varies between 33 and 53%. The selection of empirical antimicrobials to be included in treatment protocols of the most common infections depends on the strong interrelationship between patient characteristics, predominant pathogens in each focus. and antimicrobials used for treatment. Epidemiological studies carried out in the past have identified the microorganisms most frequently responsible for community-acquired and nosocomial infections in patients admitted to ICUs. Susceptibility to antimicrobial agents may be different between each geographical area, between each hospital and even within the same hospital service. In addition, susceptibility patterns may change temporarily in relation to the use of particular antimicrobials or in association with other unknown factors so that assessment of endemic antimicrobial resistance patterns is very useful in order to tailor the antimicrobial regimens of therapeutic protocols. Antimicrobial use should not be a routine procedure. The clinical course of the patient (an indicator of effectiveness) should be closely monitored as well as the possible appearance of adverse effects and/or multiresistant pathogens. Controls are based on the assessment of plasma drug concentrations and microbiological surveillance to detect the presence of multiresistant strains or new antibacterial-resistant pathogens. Prevention of the development of multiresistant pathogens is the main goal of the ICU antimicrobial policy. Although a series of general strategies to reduce the presence of multiresistant pathogens have been proposed, the implementation of these recommendations in ICUs requires the cooperation of a member of the intensive care team.

Renal transport of antibiotics and nephrotoxicity: a review

The renal excretion of a drug can essentially be divided schematically into three functional processes: glomerular filtration, tubular reabsorption and tubular secretion. When assessing nephrotoxicity, the tubular secretion system, which allows transport of the drug from the blood to the urine via the tubular cells, is particularly important. Historically, two distinct tubular secretion mechanisms have been described for drugs: one via organic cations and the other via organic anions. More recently, a third tubular secretion mechanism has been identified, mediated by P-glycoprotein. In the present review, a number of examples will be given relating to antibiotic-induced kidney damage determined via the tubular reabsorption mechanism (aminoglycosides, amphotericin B) and via the tubular secretion mechanism (cephalosporins, vancomycin), respectively. Drug transport within the tubular cells is the first fundamental stage in the onset of the nephrotoxic process. Knowledge of these concepts is important for the prevention of iatrogenic kidney damage, particularly in patients with underlying disease receiving concomitant treatment with several potentially nephrotoxic molecules.

Once-daily versus multiple-daily gentamicin in infants and children

In this prospective randomized trial, the efficacy and safety of once-daily administration of gentamicin were compared with multiple-daily administration in infants and children. In addition, pharmacokinetic variables were calculated. Gentamicin therapy was started at a dose of 5 mg/kg per day under individual dose or dosage interval adjustments to achieve target levels. Fifty-two infants and children aged 1 month (postterm) to 16 years were enrolled. The duration of fever from the start of therapy, the percentage decline of C-reactive protein (CRP) on day 3 of treatment, and the clinical outcome were used as efficacy parameters. Nephrotoxicity was evaluated using creatinine serum levels. Basic characteristics in both groups were comparable. A good clinical response was observed in both groups. Fever may have resolved faster with multiple-daily administration, but this was not statistically significant. The percentage of decline of CRP was also comparable in both groups. Nephrotoxicity occurred in six patients, three per group. Many patients were too ill or too young to perform hearing tests, but no clinical signs of ototoxicity were observed. Mean doses of 6.8 mg/kg per day (multiple-daily administration) and 7.3 mg/kg per day (once-daily administration) were necessary to meet the target gentamicin levels. Triple-daily doses had to be reduced to a twice-daily regimen in 17 of 26 children. Dose and dosage interval adaptations can be performed by Bayesian forecasting using a one-compartment model with one set of K(e) and V(d) parameters. The authors consider both regimens equally effective, with a comparable incidence of nephrotoxicity. A starting dose of 6.5 mg/kg once daily is advised.

Infections in patients undergoing peritoneal dialysis

Considering experience acquired in the past years, it seems as though physicians have reached a plateau in the frequency of peritonitis. A peritonitis rate of 1 every 2 patient years may be acceptable. Further reduction of this peritonitis rate will require inordinately large efforts on all fronts. One will have to consider what are the acceptable costs and risks of peritonitis in patients on peritoneal dialysis. New developments in catheter technology, improved connections, better understanding of patient selection and training programs, improved diagnostic and therapeutic methods in the management of peritonitis, and understanding of the infectious and immune processes are eagerly awaited developments.

Population pharmacokinetics of intravenous and intramuscular streptomycin in patients with tuberculosis

STUDY OBJECTIVES

To determine population pharmacokinetic parameters of streptomycin after administration of multiple intramuscular and intravenous doses.

DESIGN

Prospective, unblinded clinical study.

SETTING

Two medical centers in Denver, Colorado.

PATIENTS

Thirty patients with tuberculosis.

INTERVENTION

Patients received multiple doses of streptomycin as part of their tuberculosis treatment. They received concurrent drugs based on in vitro susceptibility data.

MEASUREMENTS AND MAIN RESULTS

Serum samples were collected over a 10-hour period and assayed by validated high-performance liquid chromatography Concentration-time data were analyzed using population methods. Streptomycin concentrations increased linearly with increasing intravenous doses. The intramuscular doses did not produce as linear a relationship, presumably because of variability in rates of and, potentially, completeness of absorption. Streptomycin elimination decreased with declining renal function. Higher, intermittent doses were well tolerated and appeared to maximize the peak concentration:minimal inhibitory concentration ratio.

CONCLUSION

Overall, pharmacokinetic parameters of streptomycin were comparable with those previously published for streptomycin and other aminoglycosides. Higher, intermittent doses maximize pharmacodynamic parameter estimates and might have advantages for treatment of tuberculosis.

Antibacterial treatment of invasive mechanical ventilation-associated pneumonia

Patients admitted to intensive care units (ICU) are at higher risk of acquiring nosocomial infections than patients in other hospital areas. This is the consequence of both a greater severity of illness with its implications (manipulation, invasiveness) and crossed infection from reservoirs inside the ICU. The most frequent nosocomial infection is invasive ventilation-associated pneumonia (VAP) which leads to an important increase in morbidity and mortality. The most important aetiological agents in VAP are bacteria, with a marked predominance of Staphylococcus aureus and Pseudomonas aeruginosa. These aetiologies may be different depending upon the type of ICU (medical, surgical, coronary) or the presence of certain risk factors (duration of mechanical ventilation before onset of pneumonia, previous exposure to antibacterials). Susceptibilities of the aetiological agents to antibacterials may also vary according to the type of ICU and over time. Data from global studies show an increase in multiresistant bacteria but these data may not be applied to a local ICU. The availability of accurate and updated information on the most frequently encountered organisms in each ICU and their susceptibilities is very important in order to provide the most adequate treatment. A controversial issue is the selection of antibacterials. According to the latest evidence the most adequate approach is a prompt administration of empirical treatment. Based on knowledge of bacterial flora in our own ICU, the choice of an adequate therapeutic regimen will decrease both morbidity and mortality. A second issue is monotherapy versus combined therapy. The most common recommendation, with a few exceptions, is to use combined therapy until microbiological results are received. Another controversy is the choice of antibacterials in the combined regimen. The most commonly recommended combination is that of a beta-lactam with an aminoglycoside, except in early-onset pneumonia without risk factors. The use of monotherapy with a cefalosporin without antipseudomonal activity or amoxicillin-clavulanic acid is the recommended regimen. Treatment should be modified based on microbiological results. There are no well documented recommendations on the prophylactic duration of treatment and it must be based on the aetiological agent and the clinical course. In summary treatment of VAP must be prompt, empirical and combined (beta-lactam plus aminoglycoside ). However, the choice of the antibacterial regimen should follow local guidelines of treatment based upon the knowledge of the most frequently isolated bacterial flora and their susceptibilities in different clinical settings.

Gentamicin dosing in critically ill patients

Gentamicin is used worldwide in the treatment of serious infections in critically ill patients. The therapeutic efficacy of gentamicin is correlated to the peak serum concentration and the adverse effects to the trough concentrations. Information concerning the pharmacodynamics in critically ill patients is scarce, but pharmacokinetic data are available. A once-daily dosage regimen has replaced multiple dosing of gentamicin in most intensive care units. No studies evaluating the superiority of either of these dosage recommendations in critically ill patients have ever been conducted. Based on 8 meta-analyses performed addressing this issue on a wide range of patients and theoretical considerations, we consider a once-daily dosage regimen feasible in critically ill patients. In septic patients the volume of distribution is significantly increased compared to normal patients, implying that the initial dose should be increased in this patient population. Additionally a general trend towards using higher loading doses (5-7 mg/kg) has been observed in USA, and the appropriateness of this dosing strategy is based on a large descriptive American study. We recommend that the initial dosage of gentamicin in critically ill hyperdynamic septic patients should be 7 mg/kg. Optimal and appropriate monitoring of the treatment with gentamicin in the critically ill patient is still an issue for further investigation. The treatment period with gentamicin should be short (3-5 days), bearing the pharmacological properties of aminoglycosides (small volume of distribution and poor tissue penetration) in mind. In patients with reduced renal function the initial dose of gentamicin should also be increased and maintenance dose reduced preferentially by prolonging the dosing intervals. However, the use of aminoglycosides in a high dose regimen in oliguric or anuric patients or patients who present with a rapidly decreasing renal function needs further consideration.

Malignancy and renal disease

A variety of renal diseases and electrolyte disorders may be associated with various malignancies or with treatment of malignancy with chemotherapeutic drugs or radiation. This article reviews renal disease in cancer patients, which constitutes a major source of morbidity and mortality.

Randomized, controlled trial comparing once daily and three times daily gentamicin in children with urinary tract infections

OBJECTIVE

To undertake population pharmacokinetic modeling and to determine the safety and efficacy of once daily (OD) gentamicin dosing in children with severe urinary tract infections (UTI).

METHODS

An open, randomized, controlled trial comparing OD with three times daily (TD) gentamicin dosing in hospitalized children ages 1 month to 12 years with UTI. Daily doses (milligrams per kg per day) of gentamicin in both groups were 7.5 (<5 years old), 6.0 (5 to 10 years old) and 4.5 (>10 years old).

RESULTS

There were 179 children enrolled (90 OD, 89 TD). Baseline clinical characteristics and pathogens were similar, except that circulatory compromise and renal cortical scintigraphic defects were more common in the OD group. Median gentamicin treatment durations were 3.0 (OD) and 2.7 (TD) days. Mean peak gentamicin concentrations were 17.3 (OD) vs. 6.4 (TD) mg/l; 99% of peak concentrations were >7 mg/l in the OD group whereas 16% of peak concentrations were <5 mg/l in the TD group. Mean trough concentrations were 0.35 (OD) vs. 0.55 (TD) mg/l. In the OD group 4% of trough concentrations were > or = 2 mg/l, whereas in the TD group only 0.7% were > or = 2 mg/l. Age or prior elevated peak concentrations did not predict high trough concentrations. Population pharmacokinetic modeling of the data fitted a one-compartment model with first order elimination. There were no clinical or bacteriologic failures. The two disease-related complications were confined to the OD group. No nephro- or ototoxicity was identified.

CONCLUSIONS

With age-appropriate dosing and measurement of serum trough concentrations before the second dose, OD gentamicin is safe and effective for the treatment of UTI requiring parenteral treatment in children aged 1 month to 12 years.

Aminoglycosides in cystic fibrosis: a descriptive study of current practice in Australia

AIM

To determine the diversity of clinical practice with respect to aminoglycosides in cystic fibrosis (CF) units within Australia.

METHOD

In April 1999, a questionnaire on the use of aminoglycosides was sent to 30 CF units across Australia. Information was collected about drug selection, dosing, monitoring and toxicity with intravenous administration.

RESULTS

Completed surveys were received from 26 of the 30 units (response rate = 86%) and all units with > 40 patients. Tobramycin was the drug of choice in all but two centres where there was equivalent use of gentamicin and tobramycin. The survey demonstrated a trend in recent years to reduce the number of doses per day with 54% of centres prescribing once daily, 23% twice daily and 23% thrice daily regimens. Initial dosing was generally based on mg/kg per day (mean 8.8, range 7.5-10 mg/kg per day). Dosing by infusion occurred in 11 of 14 units using once-daily dosing and there was equivalent use of bolus and infusion methods for multiple-daily regimens. Drug monitoring depended on dosing regimen. Units using multiple daily regimens monitored using trough +/- peak levels, whereas 50% of units using once-daily dosing used two postdose levels to alter dose. Actual toxicity, in particular nephrotoxicity, ototoxicity and vestibular toxicity was reported by 19, 27 and 12% of units, respectively.

CONCLUSION

The prescribing, dosing and monitoring of aminoglycosides in CF across Australia varies greatly. This is likely to be due to a lack of definitive evidence as to the optimum use in this patient group.

Antimicrobial pharmacodynamics

The ultimate goal of antimicrobial therapy is to provide the best possible outcomes for patients. For this to occur, the clinician should be cognizant of many clinical, microbiologic, pharmacologic, and epidemiologic data as well as fundamental pharmacodynamic concepts. An understanding of pharmacodynamic principles is essential; it forms the scientific basis for the design of dosing strategies that maximize clinical efficacy and minimize toxicity. In the 1990s, data accumulated from in vitro models of infection, animal models of infection, healthy volunteer studies, and clinical trials that have expanded knowledge on how drugs best kill microorganisms. This knowledge has enabled clinicians to establish the best modes of antibiotic administration to maximize the killing of microorganisms and to optimize clinical outcomes.

Management of infection in children with bone marrow failure

The development of new and often more successful regimens of treatment for childhood blood and malignant diseases has usually been associated with a parallel increase in infectious problems. This is because these successes have often, in the absence of new effective drugs, been achieved by increasing drug dose intensity to new limits. This chapter is not intended to deal with every possible infection, but rather to be a practical guide to the current management of infection. The last few years have seen major improvements in the development of haematopoietic growth factors, new antifungal agents, new antibiotics and new ways to use aminoglycosides. Attempts are being made to identify good and poor risk factors for the outcome of infection in order to facilitate shorter courses and possibly home or day care use of antimicrobial agents. In addition the different needs of children are being recognized in view of the restricted use of quinolones in this group and the different organisms and types of infection that they experience.

Cost Analysis of Pharmacy-Based Aminoglycoside Regimens: Once-Daily vs. Multiple Daily Dosing

A retrospective, case-controlled cost analysis was performed to compare the aminoglycoside-related costs of pharmacy-managed once-daily (ODA) and multiple-daily (MDA) gentamicin dosing in 274 patients. Outcome measures included the amount of drug and infusion-related supplies consumed, length of therapy, number of drug levels performed, and occurrence of nephrotoxicity. Costs were calculated based on outcome measures. Characteristics related to demographics, renal function, and site of infection were similar for both groups. The mean cumulative gentamicin dose per patient was greater in the ODA group (2223 mg) as compared with the MDA group (1169 mg), but median duration of therapy was similar in both groups (4 days). The ODA group required significantly fewer drug assays per patient than the MDA group (0.39 ± 0.63 and 1.1 ± 1.2, respectively; p < 0.01). Nephrotoxicity occurred in 1.4% of ODA patients and in 3% of MDA patients (p > 0.05). The mean costs per patient for the ODA and MDA groups were $85.66 and $140.61, respectively. Once-daily dosing of gentamicin was associated with a 65% reduction in therapeutic drug monitoring, a 53% reduction in rate of nephrotoxicity, and an overall reduction of 39% in total aminoglycoside-related costs (excluding cost of labor).]

Heterogeneity and statistical significance in meta-analysis: an empirical study of 125 meta-analyses

For meta-analysis, substantial uncertainty remains about the most appropriate statistical methods for combining the results of separate trials. An important issue for meta-analysis is how to incorporate heterogeneity, defined as variation among the results of individual trials beyond that expected from chance, into summary estimates of treatment effect. Another consideration is which 'metric' to use to measure treatment effect; for trials with binary outcomes, there are several possible metrics, including the odds ratio (a relative measure) and risk difference (an absolute measure). To examine empirically how assessment of treatment effect and heterogeneity may differ when different methods are utilized, we studied 125 meta-analyses representative of those performed by clinical investigators. There was no meta-analysis in which the summary risk difference and odds ratio were discrepant to the extent that one indicated significant benefit while the other indicated significant harm. Further, for most meta-analyses, summary odds ratios and risk differences agreed in statistical significance, leading to similar conclusions about whether treatments affected outcome. Heterogeneity was common regardless of whether treatment effects were measured by odds ratios or risk differences. However, risk differences usually displayed more heterogeneity than odds ratios. Random effects estimates, which incorporate heterogeneity, tended to be less precisely estimated than fixed effects estimates. We present two exceptions to these observations, which derive from the weights assigned to individual trial estimates. We discuss the implications of these findings for selection of a metric for meta-analysis and incorporation of heterogeneity into summary estimates. Published in 2000 by John Wiley & Sons, Ltd.

Once-daily dosing of aminoglycoside antibiotics

Improved understanding of the pharmacodynamics and toxicity of aminoglycoside antibiotics has resulted in the study of once-daily dosing regimens. Although studies have suggested a therapeutic advantage and possibly a decrease in toxicity with once-daily administration, these effects have been modest. The cost savings associated with once-daily aminoglycoside administration, however, makes this approach appealing. Although a syndrome of fever, tachycardia, hypotension, and rigors has been associated with once-daily dosing of gentamicin, this appears to have been the result of impurities in the antibiotic from a single offshore supplier. This syndrome has not been associated with other aminoglycoside antibiotics, and the FDA has now withdrawn its recommendation that once-daily aminoglycoside use be avoided. As with any medical regimen, the decision to use once-daily dosing of aminoglycoside agents must take into account special patient characteristics and the disease state being treated. Although once-daily dosing appears effective in limited studies in children, in individuals with neutropenia, and in individuals with cystic fibrosis, its role in gram-positive coccal endocarditis and in individuals with altered volumes of distribution remains uncertain. Further data are needed to clarify the role of once-daily dosing in these situations.

Gentamicin for the practicing urologist: review of efficacy, single daily dosing and "switch" therapy

PURPOSE

We review the literature on gentamicin, including single daily dosing and "switch" therapy.

MATERIALS AND METHODS

We used MEDLINE to search the literature from 1966 to June 1997, and then manually searched bibliographies to identify studies that our initial search might have missed.

RESULTS

Gentamicin has attractive characteristics, including wide spectrum, infrequent resistance, economy and familiarity. Although limited by well known toxicities, gentamicin remains a drug of choice for serious Gram-negative infections. Dosing strategies, such as single daily dosing and switch therapy, have renewed enthusiasm for this time-honored drug.

CONCLUSIONS

Gentamicin remains a valuable drug in urology. Once daily dosing and switch therapy offer the potential to increase effectiveness and convenience while decreasing toxicity and costs.

Aminoglycoside dosing in diabetes

Studies have evaluated the comparative efficacy, toxicity and costs associated with extended-interval vs. standard multiple daily dosing of aminoglycosides. In this case, an elderly man with diabetes and good renal function at baseline was switched from standard to extended-interval dosing. During the course of therapy there was evidence of decreased renal function. Pertinent literature was searched for, uncovered and critically evaluated to determine if and what evidence supports using extended dosing of aminoglycosides in this population. No data were found specifically evaluating the different dosing strategies in diabetic patients. However, there were many trials and several meta-analysis located that compared the two dosing strategies, most suggesting at least a cost advantage and possibly less toxicity with extended-interval dosing. Further information is needed to determine whether there is a differential risk for toxicity between these dosing regimens in patient with diabetes.

National survey of extended-interval aminoglycoside dosing

A random sample survey of 500 acute care hospitals in the United States was conducted to evaluate the adoption of extended-interval aminoglycoside dosing (EIAD). The survey revealed that EIAD has been adopted in 3 of every 4 acute care hospitals, a 4-fold increase since 1993. Of the 74.7% of hospitals reporting EIAD, 64% had written guidelines. Equal or less toxicity (87.1%), equal efficacy (76.9%), and cost-savings (65.6%) were common rationales. There has been a trend toward higher adult dosages of gentamicin (e.g., >5 mg/kg/dose) and an increase in the adoption of EIAD across all age groups (neonatal, 11%, and pediatric, 23%). Monitoring of aminoglycoside concentrations has shifted to a single determination of concentration, at 6-18 h after drug administration. The most common methods of dosage adjustment for declining renal function were an interval extension with the same dose (47%) or use of the Hartford nomogram (32%).

Endotoxin release from Escherichia coli after exposure to tobramycin: dose-dependency and reduction in cefuroxime-induced endotoxin release

OBJECTIVE

To study the release of free endotoxin from Escherichia coli exposed to varying concentrations of the penicillin-binding protein (PBP) 3-specific beta-lactam antibiotic cefuroxime, the aminoglycoside tobramycin, and a combination of the two, and to test the relationship between bacterial killing rate and endotoxin release.

METHODS

A clinical isolate of Escherichia coli in logarithmic phase was exposed to 0.1, 2, 10, and 50 x minimum inhibitory concentration (MIC) of cefuroxime, tobramycin, and a combination of the two. Samples for viable counts and endotoxin analysis were drawn immediately before and after the addition of the antibiotics and at 1, 2, 4, 6, and 24 h. All experiments were performed in triplicate. For the analysis of endotoxin, a chromogenic limulus amoebocyte lysate assay was used.

RESULTS

Endotoxin liberation was found to be proportional to the number of killed bacteria for each antibiotic regimen at each concentration level justifying the endotoxin-liberating potential to be expressed as release of endotoxin per killed bacterium, an expression that was independent of the inoculum size. At all concentration levels there was a statistically significant difference between the treatments, with the highest release of endotoxin per killed bacterium for cefuroxime, lower for tobramycin and the lowest for the combination of the two drugs (P < 0.001). With increasing doses, there was a significant reduction (P < 0.001) in the propensity to release endotoxin. When the bacterial killing rate was correlated to the propensity to release endotoxin in bacteria exposed to tobramycin or the combination of tobramycin and cefuroxime, a significant negative correlation was found (P < 0.01). This reduction in endotoxin release was not caused by an unspecific endotoxin binding of tobramycin.

CONCLUSIONS

Addition of tobramycin reduced the cefuroxime-induced endotoxin release per killed bacterium to a level which was even lower than that of tobramycin alone in spite of an increased killing rate. Increasing concentrations of tobramycin led to reduction in endotoxin release, which may be of benefit when dosing aminoglycosides once daily.

Once daily versus multiple daily dosing with intravenous aminoglycosides for cystic fibrosis

BACKGROUND

Patients with cystic fibrosis, who are chronically colonised with the organism Pseudomonas aeruginosa, often require repeated courses of intravenous aminoglycoside antibiotics for the management of pulmonary exacerbations. The properties of aminoglycosides suggest that they could be given in higher concentrations less often.

OBJECTIVES

To assess the effectiveness and safety of once-daily versus multiple-daily dosing of intravenous aminoglycoside antibiotics for the management of pulmonary exacerbations in cystic fibrosis.

SEARCH STRATEGY

We searched the Cystic Fibrosis specialist trials register held at the Cochrane Cystic Fibrosis and Genetic Disorders Group's editorial base, which comprises references identified from comprehensive electronic database searches, handsearching relevant journals and handsearching abstract books of conference proceedings. Date of the most recent search: February 2000.

SELECTION CRITERIA

All randomised controlled trials, whether published or unpublished, in which once-daily dosing of aminoglycosides has been compared with multiple-daily dosing in terms of efficacy and/or toxicity, in patients with cystic fibrosis.

DATA COLLECTION AND ANALYSIS

Both reviewers independently extracted data and assessed trial quality. Authors of one study were contacted to obtain missing information.

MAIN RESULTS

Two trials reporting results from a total of 70 patients were included in this review. Both trials compared once-daily dosing with thrice-daily dosing reporting data on Forced Expiratory Volume at one second (FEV1), Forced Vital Capacity (FVC), nutritional status and side effects. There was no significant difference in efficacy or in the incidence of ototoxicity and nephrotoxicity between treatment groups.

REVIEWER'S CONCLUSIONS

Despite a lack of difference between the two groups we feel that these results should be viewed with caution as the numbers of patients involved was small and lacks the power to detect a difference between the groups. This systematic review has highlighted the need for a well designed, adequately-powered, multicentre, randomised controlled trial assessing the efficacy of once-daily versus multiple-daily dosing of intravenous aminoglycosides for pulmonary exacerbations in cystic fibrosis.

Pharmacodynamic characterization of nephrotoxicity associated with once-daily aminoglycoside

STUDY OBJECTIVE

To characterize nephrotoxicity associated with an individualized serum concentration target-specific, once-daily aminoglycoside (ODA) program.

DESIGN

Concurrent and retrospective study.

SETTING

University-affiliated trauma hospital.

PATIENTS

Two hundred patients treated with ODA and 100 treated with individualized traditional dosing (TDA).

INTERVENTIONS

Empiric dosing for both groups was based on patient-specific pharmacokinetics and severity of infection. Regimens were modified according to predetermined target maximum and minimum serum concentrations for both groups.

MEASUREMENTS AND MAIN RESULTS

Nephrotoxicity occurred in 7.5% patients treated with ODA and 14.7% receiving TDA (p=0.05). Minimum serum concentrations, length of aminoglycoside therapy, and cumulative area under the curve (AUC) were all dependently related to nephrotoxicity, and concomitant vancomycin and other nephrotoxic drugs were independently related to the disorder. The cumulative AUC was greatest in patients receiving TDA (p=0.03), and the modeled probability of becoming toxic at any given cumulative AUC was significantly greater with TDA than with ODA (p<0.01). Clinical and microbiologic outcomes were similar between groups. Maximum concentration:minimum inhibitory concentration ratios were higher (p<0.01) and number of days to organism eradication was shorter in the ODA group (p=0.04).

CONCLUSION

The trend was toward decreased nephrotoxicity in patients treated with ODA compared with TDA, and at any given cumulative AUC, the risk of toxicity was lower for ODA.

State of the evidence: current status and prospects of meta-analysis in infectious diseases

Meta-analysis is increasingly applied in infectious diseases to summarize clinical data and to evaluate the strength, diversity, and deficiencies of evidence for medical questions of interest. We present an overview of the current status of meta-analysis in the area of infectious diseases and the lessons learnt from its applications. Recently published meta-analyses show that several important areas of research on infectious diseases lack sufficient randomized evidence. Often evidence is scattered across a large number of small trials, making meta-analysis a promising way to integrate diverse results. Quality of trials in the field is often poor. There are several examples where evidence was accumulated primarily for marketing rather than for scientific purposes. Finally, meta-analyses are also raising the problem of what constitutes clinically significant treatment benefits, as well as interesting issues about the reproducibility of clinical evidence and its evolving nature. The increasing applications of meta-analytic methods in the study of infectious diseases may enhance data sharing and international collaborations.

An open, randomized, multicentre study comparing the use of low-dose ceftazidime or cefotaxime, both in combination with netilmicin, in febrile neutropenic patients. German Multicentre Study Group

To reduce drug acquisition costs, the clinical and bacteriological efficacy of low-dose ceftazidime i.v. (1 g tid) was compared with cefotaxime i.v. (2 g tid). Both regimens were combined with netilmicin i.v. (2 mg/kg bodyweight tid), in an open, randomized, multicentre trial in febrile neutropenic patients. The addition of antibiotics for gram-positive coverage was part of the protocol; alteration in the antibiotics for gram-negative cover or premature discontinuation of the study antibiotics were judged as failure. One hundred and eighty six patients were randomized by nine German centres, the patients matched for age, underlying diseases and duration of neutropenia (median duration 14 days) in both treatment arms. Infections were documented microbiologically in 29% of the patients, clinically in 16% and suspected (fever of unknown origin) in 102/186 patients (55%). The 82 pathogens isolated were predominantly gram-positive bacteria. In an intent-to-treat analysis, the overall response rate without modification at the final evaluation was 58% in the ceftazidime group and 34% in the cefotaxime group (P < 0.01). The success rates with modification were 84% and 64%, respectively. The failure rate in a highly immunosuppressed subgroup of the patients (bone marrow transplant recipients) was higher for cefotaxime (53%) than for the ceftazidime arm (14%) (P < 0.001). Response rates were significantly higher in the ceftazidime group for patients with microbiologically documented and possible infections. No major bacterial superinfections occurred in the low-dose treatment arm. The tolerability was good for both regimens. Low-dose ceftazidime combined with netilmicin proved to be superior to recommended doses of cefotaxime/netilmicin in febrile neutropenic patients.

Antibiotics in neonatal infections: a review

The bacteria most commonly responsible for early-onset (materno-fetal) infections in neonates are group B streptococci, enterococci, Enterobacteriaceae and Listeria monocytogenes. Coagulase-negative staphylococci, particularly Staphylococcus epidermidis, are the main pathogens in late-onset (nosocomial) infections, especially in high-risk patients such as those with very low birthweight, umbilical or central venous catheters or undergoing prolonged ventilation. The primary objective of the paediatrician is to identity all potential cases of bacterial disease quickly and begin antibacterial treatment immediately after the appropriate cultures have been obtained. Combination therapy is recommended for initial empirical treatment in the neonate. In early-onset infections, an effective first-line empirical therapy is ampicillin plus an aminoglycoside (duration of treatment 10 days). An alternative is ampicillin plus a third-generation cephalosporin such as cefotaxime, a combination particularly useful in neonatal meningitis (mean duration of treatment 14 to 21 days), in patients at risk of nephrotoxicity and/or when therapeutic monitoring of aminoglycosides is not possible. Another potential substitute for the aminoglycoside is aztreonam. Triple combination therapy (such as amoxicillin plus cefotaxime and an aminoglycoside) could also be used for the first 2 to 3 days of life, followed by dual therapy after the microbiological results. In late-onset infections the combination oxacillin plus an aminoglycoside is widely recommended. However, vancomycin plus ceftazidime (+/- an aminoglycoside for the first 2 to 3 days) may be a better choice. Teicoplanin may be a substitute for vancomycin. However, the initial approach should always be modified by knowledge of the local bacterial epidemiology. After the microbiological results, treatment should be switched to narrower spectrum agents if a specific organism has been identified, and should be discontinued if cultures are negative and the neonate is in good clinical condition. Penicillins and third-generation cephalosporins are generally well tolerated in neonates. There is controversy regarding whether therapeutic drug monitoring of aminoglycosides will decrease toxicity (particularly renal damage) in neonates, and on the efficacy and safety of a single daily dose versus multiple daily doses of these drugs. Toxic effects caused by vancomycin are uncommon, but debate still exists over the need for therapeutic drug monitoring of this agent. When antibacterials are used in neonates, accurate determination of dosage is required, particularly for compounds with a low therapeutic index and in patients with renal failure. Very low birthweight infants are also particularly prone to antibacterial-induced toxicity.

Some international approaches to aminoglycoside monitoring in the extended dosing interval era

Aminoglycosides have rightly remained a cost-effective anti-microbial strategy for the treatment of gram-positive infections for some 25 years. However, in recent years there has been a review of the traditional thrice-daily administration regimen in favor of an extended dosing interval strategy that takes into account the individual patient's renal function. The general recommendations that have been provided to date have been adopted in various ways internationally. These approaches were a matter of discussion for the Clinical Pharmacokinetics Committee of the International Association of Therapeutic Drug Monitoring and Clinical Toxicology at its congress (Vancouver, Canada; November 1997), and will again be a workshop issue at the Cairns (Australia) congress of the Association (September 1999). The present report provides examples of how these practices have been applied at a group of centers from Canada (2 centers), The Netherlands, Egypt, and Australia. These reports demonstrate a variety of approaches and highlight the need for further research for assessing clinical outcomes from different dosing strategies.

Exploring heterogeneity in meta-analysis: is the L'Abbé plot useful?

By using a published meta-analysis as an example, this paper discusses the use of L'Abbe plot for investigating the potential sources of heterogeneity in meta-analysis. As compared with other graphic procedures, the L'Abbe plot is useful to identify not only the studies having different results from other studies, but also the study arms that are responsible for such differences. This may be important for determining the focus of heterogeneity investigations. Results of stochastic simulation indicate that, purely because of random variation, studies with event rates of around 50% are more likely to be identified as outliers in a L'Abbe plot. This paper also demonstrates that different methods may identify different trials as "outliers" in meta-analysis.

Prospective evaluation of the effect of an aminoglycoside dosing regimen on rates of observed nephrotoxicity and ototoxicity

The nephrotoxicity and ototoxicity associated with once-daily versus twice-daily administration of aminoglycosides was assessed in patients with suspected or proven gram-negative bacterial infections in a randomized, double-blind clinical trial. Patients who received therapy for >/=72 h were evaluated for toxicity. Patients also received concomitant antibiotics as deemed necessary for treatment of their infection. Plasma aminoglycoside concentrations, prospective aminoglycoside dosage adjustment, and serial audiologic and renal status evaluations were performed. The probability of occurrence of a nephrotoxic event and its relationship to doses and daily aminoglycoside exposure served as the main outcome measurement. One hundred twenty-three patients were enrolled in the study, with 83 patients receiving therapy for at least 72 h. For 74 patients plasma aminoglycoside concentrations were available for analysis, and the patients formed the group evaluable for toxicity. The primary infectious diagnosis for the patients who were enrolled in the study were bacteremia or sepsis, respiratory infections, skin and soft tissue infections, or urosepsis or pyelonephritis. Of the 74 patients evaluable for toxicity, 39 received doses twice daily and 35 received doses once daily and a placebo 12 h later. Nephrotoxicity occurred in 6 of 39 (15.4%) patients who received aminoglycosides twice daily and 0 of 35 patients who received aminoglycosides once daily. The schedule of aminoglycoside administration, concomitant use of vancomycin, and daily area under the plasma concentration-time curve (AUC) for the aminoglycosides were found to be significant predictors of nephrotoxicity by multivariate logistic regression analysis (P Collapse

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MESH Headings

• Adult
• Aged
• Aged, 80 and over
• Aminoglycosides
• Anti-Bacterial Agents/administration & dosage
• Anti-Bacterial Agents/adverse effects
• Anti-Bacterial Agents/pharmacokinetics
• Double-Blind Method
• Drug Administration Schedule
• Female
• Hearing/drug effects
• Humans
• Kidney/drug effects
• Male
• Middle Aged
• Prospective Studies

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Grants Collapse

Affiliation(s)

M J Rybak The Anti-Infective Research Laboratory, Department of Pharmacy Services, Detroit Receiving Hospital and University Health Center, College of Pharmacy and Allied Health Professions, Wayne State University, Detroit, Michigan 48201, USA.
B J Abate
S L Kang
M J Ruffing
S A Lerner
G L Drusano

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Once-daily gentamicin dosing in newborn infants

OBJECTIVE

We developed a simplified gentamicin dosing protocol for all neonates using a loading dose and once-daily dosing that would have an equal or lower incidence of toxicity and an equal or improved effectiveness compared with a regimen with no loading dose that included use of divided daily dosing.

METHODS

All neonatal intensive care unit patients with a postnatal age </=7 days and started on gentamicin therapy at the discretion of the attending neonatologist were evaluated in this comparative cohort study. All peak and trough serum drug levels (SDL), pertinent demographic data, and markers of potential nephrotoxicity, ototoxicity, and cure were tracked prospectively during 132 consecutive, nonrandomized courses of therapy on a new gentamicin protocol. These were compared with data retrieved retrospectively throughout 103 consecutive, nonrandomized courses of therapy in a control group.

RESULTS

Initial measured peak SDL were higher (7.8 +/- 1.1 microgram/mL vs 6.1 +/- 1.0 microgram/mL) and trough SDL were lower (0.9 +/- 0.2 microgram/mL vs 2.7 +/- 0.6 microgram/mL) in the protocol term subset, compared with the control term subset (gestational age, >/=37 weeks; weight, >/=2500 g). One hundred percent of the initial and maintenance peak SDL in term protocol neonates were 5 to 12 micrograms/mL; compared with 84% of the initial and 61% of maintenance peak SDL in the term control group. One hundred percent of the initial and maintenance trough SDL were in the desired range of <2 micrograms/mL in term protocol neonates; compared with 70% of the initial and 94% of maintenance trough SDL in the term control group. No significant differences were found in any SDL in low birth weight neonates (gestational age <37 weeks or weight <2500 g and >1500 g) in the protocol compared with the control group. The very low birth weight (weight <1500 g) protocol neonates had a significantly higher mean initial trough SDL (2.3 +/- 0.7 micrograms/mL vs 1.5 +/- 0.6 micrograms/mL) and a lower incidence of initial trough SDL <2.0 micrograms/mL (30% vs 95%) than very low birth weight neonates in the control group. No differences were seen between groups in incidence of significant rise in serum creatinine or failure of hearing screen.

CONCLUSION

A loading dose followed by once-daily dosing was shown to result in SDL in the safe and therapeutic range in all term neonates in this study. In low birth weight neonates, this regimen resulted in peak and trough SDL throughout therapy that were similar to those observed in the control group. Delaying the initiation of maintenance once-daily dosing until 36 to 48 hours after the loading dose would be expected to result in a higher incidence of initial trough SDL in target range for very low birth weight neonates.