Ceftazidime in treatment of acute pulmonary exacerbations in patients with cystic fibrosis

Pharmacokinetic and Pharmacodynamic Optimization of Antibiotic Therapy in Cystic Fibrosis Patients: Current Evidences, Gaps in Knowledge and Future Directions

Antibiotic therapy is one of the main treatments for cystic fibrosis (CF). It aims to eradicate bacteria during early infection, calms down the inflammatory process, and leads to symptom resolution of pulmonary exacerbations. CF can modify both the pharmacokinetic (PK) and pharmacodynamic (PD) profiles of antibiotics, therefore specific PK/PD endpoints should be determined in the context of CF. Currently available data suggest that optimal PK/PD targets cannot be attained in sputum with intravenous aminoglycosides. Continuous infusion appears preferable for β-lactam antibiotics, but optimal concentrations in sputum are unlikely to be reached, with some possible exceptions such as meropenem and ceftolozane. Usual doses are likely suboptimal for fluoroquinolones and linezolid, whereas daily doses of 45-60 mg/kg and 200 mg could be convenient for vancomycin and doxycycline, respectively. Weekly azithromycin doses of 22-30 mg/kg could also be appropriate for its anti-inflammatory effect. The difficulty with achieving optimal concentrations supports the use of combined treatments and the inhaled administration route, as very high local concentrations, concomitantly with low systemic exposure, can be obtained with the inhaled route for aminoglycosides, colistin, and fluoroquinolones, thus minimizing the risk of toxicity.

Molecular analysis of changes in Pseudomonas aeruginosa load during treatment of a pulmonary exacerbation in cystic fibrosis

BACKGROUND

Intravenous antibiotics for pulmonary exacerbations (PEs) of cystic fibrosis (CF) usually target Pseudomonas aeruginosa. Insights into the CF lung microbiome have questioned this approach. We used RT-qPCR to determine whether intravenous antibiotics reduced P. aeruginosa numbers and whether this correlated with improved lung function. We also investigated antibiotic effects on other common respiratory pathogens in CF.

METHODS

Sputa were collected from patients when stable and again during a PE. Sputa were expectorated into a RNA preservation buffer for RNA extraction and preparation of cDNA. qPCR was used to enumerate viable P. aeruginosa as well as Streptococcus pneumoniae, Haemophilus influenzae, Staphylococcus aureus, Burkholderia cepacia complex and Aspergillus fumigatus.

RESULTS

Fifteen CF patients were followed through 21 PEs. A complete set of serial sputum samples was unavailable for two patients (three separate PEs). P. aeruginosa numbers did not increase immediately prior to a PE, but numbers during intravenous antibiotic treatment were reduced ≥4-log in 6/18 and ≥1-log in 4/18 PEs. In 7/18 PEs, P. aeruginosa numbers changed very little with intravenous antibiotics and one patient demonstrated a ≥2-log increase in P. aeruginosa load. H. influenzae and S. pneumoniae were detected in ten and five PEs respectively, but with antibiotic treatment these bacteria rapidly became undetectable in 6/10 and 4/5 PEs, respectively. There was a negative correlation between P. aeruginosa numbers and FEV1 during stable phase (r(s)=0.75, p<0.05), and reductions in P. aeruginosa load with intravenous antibiotic treatment correlated with improved FEV1 (r(s)=0.52, p<0.05).

CONCLUSIONS

Exacerbations are not due to increased P. aeruginosa numbers in CF adults. However, lung function improvements correlate with reduced P. aeruginosa burden suggesting that current antibiotic treatment strategies remain appropriate in most patients. Improved understanding of PE characterised by unchanged P. aeruginosa numbers and minimal lung function improvement following treatment may allow better targeted therapies.

Optimization of anti-pseudomonal antibiotics for cystic fibrosis pulmonary exacerbations: II. cephalosporins and penicillins

Acute pulmonary exacerbations (APE) are well-described complications of cystic fibrosis (CF) and are associated with progressive morbidity and mortality. Despite aggressive management with two or more intravenous anti-pseudomonal agents, approximately 25% of exacerbations will result in a loss of lung function. The aim of this review is to provide an evidence-based summary of pharmacokinetic/pharmacodynamic (PK/PD), tolerability, and efficacy studies utilizing anti-pseudomonal cephalosporins (i.e., ceftazidime and cefepime) and penicillins (i.e., piperacillin-tazobactam and ticarcillin-clavulanate) in the treatment of APE and to identify areas where further study is warranted. The ceftazidime and cefepime dosing ranges from the literature are 200-400 mg/kg/day divided every 6-8 hr, maximum 8-12 g/day, and 150-200 mg/kg/day divided every 6-8 hr, up to 6-8 g/day, respectively. The literature supported dosing ranges for piperacillin and ticarcillin are 350-600 mg/kg/day divided every 4 hr, maximum 18-24 g/day of piperacillin component, and 400-750 mg/kg/day divided every 6 hr, up to 24-30 g/day of ticarcillin component, respectively. As a large portion of CF patients will not regain their lung function following an APE, we suggest the need to optimize antibiotic dosing and dosing regimens used to treat an APE in efforts to improve outcomes for CF patients infected with Pseudomonas aeruginosa. Future studies are needed to determine the clinical efficacy of higher than FDA-approved doses of ceftazidime, cefepime, and ticarcillin-clavulanate in APE. The usefulness of high dose piperacillin (>600 mg/kg/day) may be limited due to treatment-related adverse effects. Further understanding of these adverse effects in CF patients is needed.

Population pharmacokinetic comparison and pharmacodynamic breakpoints of ceftazidime in cystic fibrosis patients and healthy volunteers

Despite the promising activity of ceftazidime against Pseudomonas aeruginosa and Burkholderia cepacia, there has not yet been a study that directly compared the pharmacokinetics (PK) of ceftazidime in cystic fibrosis (CF) patients and healthy volunteers by population PK methodology. We assessed the population PK and PK/pharmacodynamic (PD) breakpoints of ceftazidime in CF patients and healthy volunteers. Eight CF patients (total body weight [WT] [average +/- standard deviation] = 42.9 +/- 18.4 kg) and seven healthy volunteers (WT = 66.2 +/- 4.9 kg) received 2 g ceftazidime as a 5-min intravenous infusion. High-performance liquid chromatography (HPLC) was used for drug analysis, and NONMEM (results reported), S-ADAPT, and NPAG were used for parametric and nonparametric population PK modeling. We considered linear and allometric body size models to scale clearance and volume of distribution. Monte Carlo simulations were based on a target time of non-protein-bound plasma concentration of ceftazidime above MIC of > or =65%, which represents near-maximal killing. Unscaled total clearance was 19% lower in CF patients, and volume of distribution was 36% lower. Total clearance was 7.82 liters/h for CF patients and 6.68 liters/h for healthy volunteers with 53 kg fat-free mass. Allometric scaling by fat-free mass reduced the between-subject variability by 32% for clearance and by 18 to 26% for volume of both peripheral compartments compared to linear scaling by WT. A 30-min ceftazidime infusion of 2 g/70 kg WT every 8 h (q8h) achieved robust (> or =90%) probabilities of target attainment (PTAs) for MICs of < or =1 mg/liter in CF patients and < or =3 mg/liter in healthy volunteers. Alternative modes of administration achieved robust PTAs up to markedly higher MICs of < or =8 to 12 mg/liter in CF patients for 5-h infusions of 2 g/70 kg WT q8h and < or =12 mg/liter for continuous infusion of 6 g/70 kg WT daily.

Circulating RNA transcripts identify therapeutic response in cystic fibrosis lung disease

RATIONALE

Circulating leukocyte RNA transcripts are systemic markers of inflammation, which have not been studied in cystic fibrosis (CF) lung disease. Although the standard assessment of pulmonary treatment response is FEV(1), a measure of airflow limitation, the lack of systemic markers to reflect changes in lung inflammation critically limits the testing of proposed therapeutics.

OBJECTIVES

We sought to prospectively identify and validate peripheral blood leukocyte genes that could mark resolution of pulmonary infection and inflammation using a model by which RNA transcripts could increase the predictive value of spirometry.

METHODS

Peripheral blood mononuclear cells were isolated from 10 patients with CF and acute pulmonary exacerbations before and after therapy. RNA expression profiling revealed that 10 genes significantly changed with treatment when compared with matched non-CF and control subjects with stable CF to establish baseline transcript abundance. Peripheral blood mononuclear cell RNA transcripts were prospectively validated, using real-time polymerase chain reaction amplification, in an independent cohort of acutely ill patients with CF (n = 14). Patients who responded to therapy were analyzed using general estimating equations and multiple logistic regression, such that changes in FEV(1)% predicted were regressed with transcript changes.

MEASUREMENTS AND MAIN RESULTS

Three genes, CD64, ADAM9, and CD36, were significant and independent predictors of a therapeutic response beyond that of FEV(1) alone (P < 0.05). In both cohorts, receiver operating characteristic analysis revealed greater accuracy when genes were combined with FEV(1).

CONCLUSIONS

Circulating mononuclear cell transcripts characterize a response to the treatment of pulmonary exacerbations. Even in small patient cohorts, changes in gene expression in conjunction with FEV(1) may enhance current outcomes measures for treatment response.

Antibiotic use in Cystic Fibrosis

Chronic pulmonary infections contribute significantly to the morbidity and mortality of patients with CF. The primary pathogens are Pseudomonas aeruginosa (PA) and Staphylococcus aureus. Hemophilus influenzae has been isolated from a significant number of patients also. A number of the β-lactam and aminoglycoside antibiotics reportedly have altered pharmacokinetic variables in CF. Therapy of acute pulmonary deterioration consists of intravenous antibiotics for two weeks. Antibiotic selection is based on culture and sensitivity results. Currently, the combination of a broad-spectrum penicillin and an aminoglycoside seems to provide the best results. Prophylactic antibiotics are effective if the primary isolates are sensitive to the agents used. Chronic PA infections are problematic because effective oral agents are not available. Aerosolized antibiotics do not improve results over adequate systemic therapy for acute exacerbations. Questions regarding optimal dosages, frequency, and duration of therapy remain.

A retrospective analysis using Monte Carlo simulation to evaluate recommended ceftazidime dosing regimens in healthy volunteers, patients with cystic fibrosis, and patients in the intensive care unit

BACKGROUND

Over the past decades, the relationship between the pharmacokinetic (PK) properties of antibiotics, MICs, and clinical effects has been increasingly well understood. Interpatient variability in the PK profile, however, has only recently been recognized as a major factor in predicting the outcome in individual patients and establishing breakpoints for clinical susceptibility. Most predictions to date have used data from healthy volunteers.

OBJECTIVE

The purpose of this study was to perform Monte Carlo simulations of the PK/pharmacodynamic relationships of ceftazidime to assess whether the probability of target attainment (PTA) differed significantly between 3 distinct populations. To that end, population PK models of ceftazidime were developed for the 3 populations.

METHODS

Serum concentration-time data from earlier studies in healthy volunteers (n = 8), patients with cystic fibrosis (CF) (n = 17), and patients in the intensive care unit (ICU) (n = 6) were used to obtain population PK parameter estimates and covariance matrices using the nonparametric adaptive grid program. The PTA for each group was obtained using 10,000 patient simulations for dosing regimens of 1000 and 2000 mg q8h over a range of MICs and percentages of time that concentrations of unbound drug remained above the MIC (%T > MIC).

RESULTS

The relationship between the MIC and the population mean %T > MIC, as well as the PTA profiles, differed markedly between the 3 groups as a result of both differences and variations in V(d) and Cl. Breakpoints based on a 100% PTA for a %T > MIC of 60% were < or = 4, 0.5, and 0.5 mg/L in healthy volunteers, patients with CF, and patients in the ICU, respectively. However, when PTA values between 90% and 100% were reevaluated and differences in clinical dosing regimens were accounted for, the resulting breakpoints were identical in the 3 groups.

CONCLUSIONS

PK parameter estimates for ceftazidime based on data from a small group of healthy volunteers resulted in a clinical susceptibility breakpoint comparable to those for patients with CF and patients in the ICU. Based on the study findings, this breakpoint would be < or = 4 mg/L. Patients suspected of having unusually high rates of clearance should be monitored closely.

Defining a pulmonary exacerbation in cystic fibrosis

OBJECTIVES

Despite the central importance of pulmonary exacerbations (PExs) as an outcome measure in cystic fibrosis clinical trials, no standardized definition of PEx exists. We conducted a prospective, multicenter study to establish a standardized PEx definition and score for use in clinical trials, based on clinical status rather than on treatment decisions.

STUDY DESIGN

Subjects were 246 patients enrolled in the placebo arm of a randomized, controlled trial of tobramycin for inhalation. Physician-investigators completed PEx questionnaires on all subjects at scheduled intervals during the 6-month study, indicating new or worsening symptoms, physical examination findings, and impression of PEx status (presence or absence and severity). Logistic regression was used to assess the relative importance of each of the characteristics in predicting a PEx.

RESULTS

We developed 2 PEx scores that use easily ascertained symptoms and chest examination findings; one also includes change in forced expiratory volume in 1 second over the preceding month. Both scores were sensitive and specific for predicting the presence of a PEx (sensitivity, 86%; specificity, 86%). The scores were validated in subjects in the intervention arm of the trial.

CONCLUSION

We hope that the proposed PEx score might serve as a standardized outcome measure for future clinical trials in cystic fibrosis, allowing meaningful comparisons of study results.

Increasing dose regimen in children with reactions to ceftazidime

BACKGROUND

Of 87 consecutive patients with cystic fibrosis treated with 859 courses of intravenous ceftazidime, 15 patients experienced reactions to drugs.

OBJECTIVE

To see if by varying the means of administration further courses of treatment with ceftazidime could be tolerated in subjects who had experienced drug reactions.

METHODS

Starting with a dose of 1 mg per hour, and doubling the dose every hour, ceftazidime was administered at increasing dosage by continuous infusion, reaching a rate of 150-300 mg/kg/day. Thereafter the full daily dose was given in three divided bolus doses. For patients who tolerated the maximum infusion rate but reacted adversely to bolus doses, the procedure was restarted, and once the normal daily dose rate had been achieved, treatment was completed by continuous intravenous infusion rather than bolus doses.

RESULTS

Of the 15 patients, three patients with urticaria and four patients with nonurticarial itchy rash tolerated further courses of ceftazidime without adverse reactions, and two patients have not had further treatment with intravenous antibiotics. The increasing dose regimen was tolerated in five of the remaining six patients, and further courses of treatment were tolerated in the four patients in whom this was required. One patient had recurrent urticaria despite three attempts at using the regimen, and treatment was given with alternative antibiotics.

CONCLUSION

A continuous drug infusion regimen of starting at a very low dosage and then increasing the dosage offers the potential for further treatment in some children with cystic fibrosis with adverse reactions to ceftazidime.

Correlation between activity of beta-lactam agents in vitro and bacteriological outcome in acute pulmonary exacerbations of cystic fibrosis

A study was conducted to determine whether a direct relationship exists between beta-lactam and/or aminoglycoside activity measured in vitro and bacteriological outcome in acute pulmonary exacerbations of cystic fibrosis. Twenty-seven patients, aged between 6 months and 24 years (mean age 10 1/2 years), were included in the study and received 41 i.v. courses of a beta-lactam agent combined with an aminoglycoside. A total of 63 Pseudomonas aeruginosa strains were found in sputum taken on admission at densities exceeding 10(6) cfu/g of sputum. For each episode, the serum inhibitory quotient (SIQ) and the serum bactericidal quotient (SBQ) of the beta-lactam agent and of the aminoglycoside administered were determined for the Pseudomonas aeruginosa isolate(s). The SIQs and SBQs were calculated by dividing the average peak serum levels achievable in the patients by the minimal inhibitory concentrations and minimal bactericidal concentrations, respectively. The SIQs and SBQs were compared to bacteriological outcome. Bacteriological success was defined as a decrease of 2 log10 counts or more in the Pseudomonas aeruginosa density in sputum between days 0 and 7 of therapy. The SIQ and SBQ of beta-lactam agents were good predictors of bacteriological outcome: SIQs of < 1:16 were 100% predictive of failure (chi 2 28; p < 0.001) and of > or = 1:64 were 92.9% predictive of success (chi 2 35.68; p < 0.001); SBQs of < 1:8 were 100% predictive of failure (chi 2 42.78; p < 0.001) and of > or = 1:32 were 95.8% predictive of success (chi 2 31.5; p < 0.001). Aminoglycoside SIQs and SBQs were not predictive of outcome.

Comparative activity of cefepime, alone and in combination, against clinical isolates of Pseudomonas aeruginosa and Pseudomonas cepacia from cystic fibrosis patients

The comparative in vitro activity and synergy of cefepime were evaluated with clinical isolates of Pseudomonas aeruginosa and Pseudomonas cepacia from cystic fibrosis patients. The activity of cefepime, both alone and in combination, was comparable to those of other antibiotics. The clinical efficacy of cefepime in cystic fibrosis patients merits investigation.

Serious pediatric infections

Third-generation cephalosporins are important additions to the range of antibiotics available for treating children with serious bacterial infections. They are highly active against the common pathogens, which cause bacterial meningitis in children. Strains of Haemophilus influenzae type b resistant to both ampicillin and chloramphenicol, and Streptococcus pneumoniae relatively resistant to penicillin remain susceptible to cefotaxime and ceftriaxone. Escherichia coli, Klebsiella pneumoniae, Citrobacter diversus, as well as the other more common gram-negative bacilli isolated from neonates and children are susceptible to these agents. However, Listeria monocytogenes is not cephalosporin-sensitive. Ceftazidime is the only third-generation cephalosporin useful for treating serious infections due to Pseudomonas aeruginosa in children. As with other beta-lactam antibiotics, the clearance of cephalosporins is prolonged in neonates, particularly premature babies. Cefotaxime and ceftriaxone are equivalent to ampicillin and chloramphenicol for the treatment of bacterial meningitis in children over two to three months of age with respect to neurologic outcome and safety, despite the in vitro activity of cefotaxime and ceftriaxone being much greater than the standard antibiotics for the meningeal pathogens. Cefotaxime and ceftriaxone are effective in the treatment of serious gram-negative infections in children. In many instances, ceftriaxone can be administered once daily, which allows for more convenient therapy, particularly on an outpatient basis. Although controversial, ceftazidime has been used as single-agent therapy for empiric treatment of neutropenic immunocompromised children with fever.

Clinical pharmacology of antibiotics and other drugs in cystic fibrosis

The disposition of many drugs in cystic fibrosis is abnormal. In general, changes in pharmacokinetics include: increased volume of distribution, decreased plasma concentration, and enhanced renal and sometimes non-renal elimination of drugs. Pathophysiology of the disease important for drug disposition includes: (a) hypersecretion of gastric acid and duodenal secretions which are of small volume, viscous and low in bicarbonate; (b) increased intestinal permeability to some sugars and probe substances; (c) hypergammaglobulinaemia and sometimes hypoalbuminaemia; (d) significant elevation of free fatty palmitoleic acid level and decreased low-density and high-density serum lipoproteins; (e) an average increase by 30 to 45% in plasma volume in patients with cystic fibrosis who have moderately severe pulmonary disease, right ventricle hypertrophy and dilatation, which occurs in 15 to 35% of patients with a Shwachman score of 81 to 100; (f) abnormal bile acid metabolism and enterohepatic recirculation; and (g) enlarged kidneys and glomerulomegaly with increased glomerular filtration rate, tubular clearance and urine flow rate in some patients with cystic fibrosis. Delayed absorption from the gastrointestinal tract has been reported in patients with cystic fibrosis for cloxacillin, epicillin, clindamycin, ciprofloxacin and probably for cephalexin, para-aminobenzoic acid and chloramphenicol. A possible increased absorption was reported for cimetidine. Of 7 drugs studied only theophylline had significantly decreased plasma protein binding. An increased volume of distribution and increased renal clearance reported for several drugs is caused mainly by increases in plasma volume and urine flow rate in many of these patients. Possible increased elimination of some drugs in bile (which probably results from bile acid malabsorption) and in bronchial secretions (which are abundant in some cystic fibrosis patients with acute pulmonary infection) may explain enhanced non-renal elimination of these drugs. The metabolism of cimetidine in cystic fibrosis was reported not to be changed significantly compared to control subjects.

Does monotherapy of pulmonary infections in cystic fibrosis lead to early development of resistant strains of Pseudomonas aeruginosa?

We report the development of ceftazidime-resistant strains of Pseudomonas aeruginosa in a small population of cystic fibrosis patients who had ceftazidime monotherapy over a 5-year period as clinically indicated. The background rate of less than 30% of patients with a ceftazidime-resistant strain of P. aeruginosa in their sputum each month is similar to the resistance rate to other anti-pseudomonas antibiotics that have seldom been used here. In practice this resistance has meant that for about 10% of patients each month consideration has to be given to the use of an agent other than ceftazidime.

Efficacy of inhaled amikacin as adjunct to intravenous combination therapy (ceftazidime and amikacin) in cystic fibrosis

Eighty-seven patients with cystic fibrosis were admitted to hospital with an acute exacerbation of pulmonary symptoms associated with isolation of Pseudomonas aeruginosa from sputum. The patients were randomly allocated to receive intravenously administered ceftazidime (250 mg/kg/day) and amikacin (33 mg/kg/day) alone or with inhaled amikacin (100 mg twice a day). Other aspects of the 2-week treatment were constant. The two therapy groups were comparable in all aspects. At the completion of therapy, the addition of aerosolized amikacin produced temporary eradication of P. aeruginosa in 70% of the patients, compared with 41% in the intravenous therapy only group (P less than 0.02). Suppression of P. aeruginosa in sputum cultures was correlated with the amikacin sputum concentrations. However, both regimens resulted in similar improvements in clinical, radiologic, laboratory, and pulmonary function measurements, and within 4 to 6 weeks most patients were recolonized with P. aeruginosa. There was no serious toxicity or adverse effect. In patients with cystic fibrosis, the addition of aerosol aminoglycoside to systemic antipseudomonal combination therapy is not clinically beneficial.

High dose treatment with antibiotics in cystic fibrosis--a reappraisal with special reference to the pharmacokinetics of beta-lactams and new fluoroquinolones in adult CF-patients

In this review we analyzed the pharmacokinetic basis for high dose treatment with antibiotics of patients with cystic fibrosis. Both our results and those from other well designed pharmacokinetic studies do not support the view that low blood levels of antibacterials are a common feature of CF. We were unable to detect a decrease in absorption, nor could we find evidence for enhanced elimination of antibacterials in CF. Both these factors have been considered responsible for reducing the plasma (and tissue) levels of antibiotics. Most recent studies on kidney function are in agreement with these findings, since neither inulin nor creatinine clearance differ between CF-patients and healthy volunteers. In contrast to previous discussion, the volume of distribution (Vdss) was not elevated for any compound. The rational of weight correction of volume terms like Vdss or total clearance has never been clearly demonstrated and should therefore not be used without prior proof of relevance. Since the variability of pharmacokinetic parameters of antibiotics in CF-patients may be considerable, we suggest that a dose increase of 20-30% may be justified, but cannot agree with two to fourfold increases in dosage as previously proposed and applied in many CF-centers. Until more findings become available for non-adult CF-patients, these conclusions are only valid for adult CF-patients.

Randomized double-blind evaluation of ceftazidime dose ranging in hospitalized patients with cystic fibrosis

Eighty-five patients with cystic fibrosis who were experiencing an acute infectious exacerbation of their disease were randomized in double-blind fashion to receive either 50 or 75 mg of ceftazidime per kg (body weight) per dose administered intravenously every 8 h for 14 days. Three patients were dropped from the study within 4 days of enrollment for reasons unrelated to drug administration. The total daily dose of ceftazidime administered was restricted by protocol design and was independent of the body weight of the patient. Thus, for datum analysis, patients were separated into three ceftazidime dosage groups (denoted as range of milligrams per kilogram per dose): group 1, 22 to 44.5; group 2, 46.3 to 56.6; and group 3, 66.7 to 80.6. Ceftazidime monotherapy had no effect on sputum colony counts for any Pseudomonas cepacia isolate. In contrast, a substantial reduction in Pseudomonas aeruginosa sputum colony counts was observed, and from 19 to 31% of isolates were suppressed greater than or equal to 10(5) CFU/ml after 14 days of therapy. Bacterial resistance in vitro was not observed, although a trend for increasing ceftazidime MICs was observed for group 1 patients (P less than 0.05). Overall, clinical response appeared independent of drug dose, and no relationship could be identified between the reduction in P. aeruginosa sputum colony counts and clinical outcome. Adverse effects of ceftazidime were mild and transient, necessitating drug discontinuation in one patient. These data suggest that the clinical response to ceftazidime in patients with cystic fibrosis may be maximal with 50 mg/kg per dose (150 mg/kg per day) up to a total daily dose of 6 g.

Treatment of respiratory tract infections with cephalosporin antibiotics

Infections of the respiratory tract are among the most common causes for antibiotic prescribing. Their diagnosis within the community is generally limited to clinical criteria, and microbiological information is frequently lacking. Hospitalised patients with respiratory tract infections are more likely to undergo diagnostic sampling, but difficulties remain in reliably defining a microbial aetiology, thereby providing a confident basis for antibiotic selection. In considering the role of the cephalosporins in the treatment of respiratory tract infections, over 500 published articles have been reviewed. The pharmacokinetic considerations are discussed and the limitations of existing methodology are emphasised. Individual agents are reviewed by site of sepsis and conclusions are drawn from both comparative and non-comparative studies and in relation to currently recommended regimens. Although oral cephalosporins are widely used to treat upper respiratory tract infections, none is considered ideal, especially where Haemophilus influenzae is pathogenic. In the case of lower respiratory tract infections the beta-lactamase stable parenteral cephalosporins have become widely used to treat pneumonia in hospitalised patients, especially where Gram-negative enteric bacilli are of aetiological importance. However, the lack of activity of these drugs against Legionella spp., Mycoplasma pneumoniae and Coxiella burnetii must be emphasised. Another area of increasing use is in the treatment of infective exacerbations in patients suffering from cystic fibrosis of the lungs where Pseudomonas aeruginosa is pathogenic; ceftazidime in particular has proved a useful alternative to earlier antipseudomonal penicillin antibiotics.

Differences in drug susceptibility between isolates of Pseudomonas cepacia recovered from patients with cystic fibrosis and other sources and its relationship to beta-lactamase focusing pattern

Pseudomonas cepacia, a significant pulmonary pathogen among children with cystic fibrosis (CF), often possesses an inducible beta-lactamase. The beta-lactamase isoelectric focusing pattern and beta-lactam susceptibility of CF and non-CF isolates of P. cepacia were compared. Against all of the test strains, ceftazidime and piperacillin were more effective than aztreonam. More CF isolates were resistant to 8 micrograms/ml of ceftazidime than non-CF isolates. Isoelectric focusing of cefoxitin-induced, cell-free preparations of the CF isolates produced significantly more bands than comparable preparations of non-CF isolates. Organisms producing a beta-lactamase band that focused in the pH range of 8.5 to 8.7 were significantly more resistant to 8 micrograms/ml of ceftazidime than other isolates. The increased resistance of CF isolates of P. cepacia to ceftazidime may be the result of the production of a specific bacterial beta-lactamase.

Antibiotic activity in sputum

Pulmonary infection in cystic fibrosis (CF) is primarily a purulent tracheobronchitis. Antibiotics are available that are active in vitro against bacteria isolated from sputum from patients with CF. Despite efficacious antibiotic concentrations in serum, however, the results of treatment are frequently suboptimal. A widely accepted explanation for this limited efficacy is poor penetration of orally or intravenously administered antibiotics into respiratory secretions. The bioactivity of antibiotics in respiratory secretions is not identical to that found in vitro. Laboratory conditions are standardized and selected to approximate serum. Deviations from these conditions can markedly influence the results. Differences in composition between sputum and laboratory culture media, as well as variation in growth and metabolism of the pathogen in respiratory secretions, must be considered when predicting in vivo activity in sputum. Thus, when defining criteria for antibiotic susceptibility or resistance in the treatment of pulmonary infection in patients with CF, the concentrations achievable in bronchial secretions as well as the bioactivity in this environment should be considered.

Management of acute pulmonary exacerbations in cystic fibrosis: a critical appraisal

Optimal management of acute exacerbations of pulmonary symptoms in patients with cystic fibrosis remains questionable. The underlying cause of such exacerbations has not been identified, and the microbiology of the sputum does not differ substantially during these exacerbations. Despite the absence of conclusive evidence that antibiotic therapy enhances treatment of cystic fibrosis, the consensus favors its use. Various combination and single-agent therapies with aminoglycosides, cephalosporins, and beta-lactam antibiotics are reviewed critically. The importance of high activity against Pseudomonas strains is addressed, as is the potential value of antibiotic prophylaxis. The drawbacks of aminoglycoside treatment are reported. No evidence proves the superiority of combination therapy over monotherapy. Recent results suggesting the effectiveness of monotherapy with piperacillin or ceftazidime are encouraging and deserve follow-up to test continued efficacy and the absence of development of resistant antibiotic strains. Further investigation into the prevention of acute pulmonary exacerbations in cystic fibrosis is essential.

Antibiotic use in cystic fibrosis

Chronic pulmonary infections contribute significantly to the morbidity and mortality of patients with CF. The primary pathogens are Pseudomonas aeruginosa (PA) and Staphylococcus aureus. Hemophilus influenzae has been isolated from a significant number of patients also. A number of the beta-lactam and aminoglycoside antibiotics reportedly have altered pharmacokinetic variables in CF. Therapy of acute pulmonary deterioration consists of intravenous antibiotics for two weeks. Antibiotic selection is based on culture and sensitivity results. Currently, the combination of a broad-spectrum penicillin and an aminoglycoside seems to provide the best results. Prophylactic antibiotics are effective if the primary isolates are sensitive to the agents used. Chronic PA infections are problematic because effective oral agents are not available. Aerosolized antibiotics do not improve results over adequate systemic therapy for acute exacerbations. Questions regarding optimal dosages, frequency, and duration of therapy remain.

Ceftazidime in the treatment of pediatric patients with severe urinary tract infections due to Pseudomonas spp

Fifteen pediatric patients with complicated urinary tract infections due to Pseudomonas spp. were treated for 10 to 18.5 days with ceftazidime administered intramuscularly twice daily. Urine sterilization during therapy was obtained in all patients. Three patients had relapses which were cured with a second course of ceftazidime. Minor liver damage, eosinophilia, and Candida superinfection developed in one patient each.