Pharmacokinetics of imipenem and cilastatin in patients with cystic fibrosis

Identification of Antibiotics in Surface-Groundwater. A Tool towards the Ecopharmacovigilance Approach: A Portuguese Case-Study

Environmental monitoring, particularly of water, is crucial to screen and preselect potential hazardous substances for policy guidance and risk minimisation strategies. In Portugal, extensive data are missing. This work aimed to perform a qualitative survey of antibiotics in surface- groundwater, reflecting demographic, spatial, consumption and drug profiles during an observational period of three years. A passive sampling technique (POCIS) and high-resolution chromatographic system were used to monitor and analyse the antibiotics. The most frequently detected antibiotics were enrofloxacin/ciprofloxacin and tetracycline in surface-groundwater, while clarithromycin/erythromycin and sulfamethoxazole were identified only in surface water. The detection of enzyme inhibitors (e.g., tazobactam/cilastatin) used exclusively in hospitals and abacavir, a specific human medicine was also noteworthy. North (Guimarães, Santo Tirso and Porto) and South (Faro, Olhão and Portimão) Portugal were the regions with the most significant frequency of substances in surface water. The relatively higher detection downstream of the effluent discharge points compared with a low detection upstream could be attributed to a low efficiency in urban wastewater treatment plants and an increased agricultural pressure. This screening approach is essential to identify substances in order to perform future quantitative risk assessment and establishing water quality standards. The greatest challenge of this survey data is to promote an ecopharmacovigilance framework, implement measures to avoid misuse/overuse of antibiotics and slow down emission and antibiotic resistance.

Clinical Pharmacokinetic and Pharmacodynamic Considerations in the Drug Treatment of Non-Tuberculous Mycobacteria in Cystic Fibrosis

Non-tuberculous mycobacteria (NTM) are an emerging group of pulmonary infectious pathogens of increasing importance to the management of patients with cystic fibrosis (CF). NTM include slow-growing mycobacteria such as Mycobacterium avium complex (MAC) and rapidly growing mycobacteria such as Mycobacterium abscessus. The incidence of NTM in the CF population is increasing and infection contributes to significant morbidity to the patient and costs to the health system. Treating M. abscessus requires the combination of multiple costly antibiotics for months, with potentially significant toxicity associated with treatment. Although international guidelines for the treatment of NTM infection in CF are available, there are a lack of robust pharmacokinetic studies in CF patients to inform dosing and drug choice. This paper aims to outline the pharmacokinetic and pharmacodynamic factors informing the optimal treatment of NTM infections in CF.

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.

Imipenem/Cilastatin: The First Carbapenem Antibiotic

Imipenem/cilastatin is the first of a new class of β-lactam antibiotics called carbapenems. The antibacterial spectrum of imipenem exceeds any antibiotic investigated to date and includes gram-positive, gram-negative, and anaerobic organisms. Only methicillin-resistant organisms, Strep. faecium, Pseudomonas cepacia, and Pseudomonas maltophilia have been shown to be resistant. Imipenem is administered in a 1:1 ratio with cilastatin, which inhibits a renal enzyme (dehydropeptidase) and improves urinary recovery of imipenem. The elimination half-life of both compounds is 1.0 hours and recommended doses are 0.25–0.5 g iv q6h. Adverse events are similar in nature and incidence to β-lactam antibiotics, with phlebitis/thrombophlebitis, diarrhea, nausea, skin rash, and elevations of hepatic enzymes most common.

Clinical studies in phase II and III trials have shown imipenem/cilastatin to be effective in soft tissue infections, endocarditis, obstetrics and gynecology, complicated urinary tract infections, mixed anaerobic-aerobic infections, osteomyelitis, bacteremias, and pneumonias. Several comparative clinical trials have shown imipenem/cilastatin to be equal in efficacy to combination therapy. Imipenem/cilastatin may prove to be an alternative to combination antibiotic therapy because of its extremely broad spectrum of activity.

Sublethal concentrations of carbapenems alter cell morphology and genomic expression of Klebsiella pneumoniae biofilms

Klebsiella pneumoniae, a Gram-negative bacterium, is normally associated with pneumonia in patients with weakened immune systems. However, it is also a prevalent nosocomial infectious agent that can be found in infected surgical sites and combat wounds. Many of these clinical strains display multidrug resistance. We have worked with a clinical strain of K. pneumoniae that was initially isolated from a wound of an injured soldier. This strain demonstrated resistance to many commonly used antibiotics but sensitivity to carbapenems. This isolate was capable of forming biofilms in vitro, contributing to its increased antibiotic resistance and impaired clearance. We were interested in determining how sublethal concentrations of carbapenem treatment specifically affect K. pneumoniae biofilms both in morphology and in genomic expression. Scanning electron microscopy showed striking morphological differences between untreated and treated biofilms, including rounding, blebbing, and dimpling of treated cells. Comparative transcriptome analysis using RNA sequencing (RNA-Seq) technology identified a large number of open reading frames (ORFs) differentially regulated in response to carbapenem treatment at 2 and 24 h. ORFs upregulated with carbapenem treatment included genes involved in resistance, as well as those coding for antiporters and autoinducers. ORFs downregulated included those coding for metal transporters, membrane biosynthesis proteins, and motility proteins. Quantitative real-time PCR validated the general trend of some of these differentially regulated ORFs. Treatment of K. pneumoniae biofilms with sublethal concentrations of carbapenems induced a wide range of phenotypic and gene expression changes. This study reveals some of the mechanisms underlying how sublethal amounts of carbapenems could affect the overall fitness and pathogenic potential of K. pneumoniae biofilm cells.

Optimization of anti-pseudomonal antibiotics for cystic fibrosis pulmonary exacerbations: I. aztreonam and carbapenems

Acute pulmonary exacerbations (APE) in cystic fibrosis (CF) are associated with loss of lung function that may require aggressive management with intravenous antibiotics. The aim of this review is to provide an evidence-based summary of pharmacokinetic/pharmacodynamic (PK/PD), tolerability, and efficacy studies utilizing aztreonam and anti-pseudomonal carbapenems (i.e., doripenem, imipenem-cilastatin, and meropenem) in the treatment of an APE, and to identify areas where further study is warranted. The current dosing recommendations in the United States and Europe for aztreonam are lower than the literature supported dosing range of 200-300 mg/kg/day divided every 6 hr, maximum 8-12 g/day. In vitro, PK/PD, and tolerability studies show the potential of doripenem 90 mg/kg/day divided every 8 hr, infused over 4 hr, maximum 6 g/day in the treatment of APE. Imipenem-cilastatin 100 mg/kg/day divided every 6 hr, maximum 4 g/day and meropenem 120 mg/kg/day divided every 8 hr, maximum 6 g/day have been shown to be tolerable and effective in the treatment of APE. With availability issues of new anti-pseudomonal agents and a large percentage of CF patients will not regain their lung function following an APE, we suggest the need to determine optimization of aztreonam and meropenem dosing in CF, as well as to determine the clinical efficacy of doripenem in the treatment of APE. The usefulness of imipenem-cilastatin may be limited due to the rapid development of resistance.

A survey of the utilization of anti-pseudomonal beta-lactam therapy in cystic fibrosis patients

The purpose of this study was to characterize the utilization of anti-pseudomonal beta-lactam antibiotics in the treatment of acute pulmonary exacerbations (APE) among Cystic Fibrosis Foundation (CFF)-accredited care centers. An anonymous national cross-sectional survey of CFF-accredited care centers was performed using an electronic survey tool (SurveyMonkey.com®). One hundred and twenty-one of 261 centers completed the survey (46%) representing 56% (14,856/26,740) of patients in the CFF Patient Registry. One hundred and nineteen of 121 (98%) respondents reported using beta-lactams for the treatment of APE. Intermittent dosing regimens constituted 155/167 (93%) reported regimens, while extended infusions were 12/167 (7%). Ceftazidime was the most commonly utilized beta-lactam comprising 74/167 (44%) of all infusions (intermittent and extended) of which 70/74 (95%) were intermittent infusions. The majority of intermittent ceftazidime regimens (56/70; 80%) were at doses lower than CFF and European guidelines recommended doses. In conclusion, a great majority of respondents use intermittent anti-pseudomonal beta-lactam antibiotics, with over half of respondents utilizing lower than guidelines recommended doses. While this is of concern, it is not known if optimization of dosing strategies according to guidelines recommendations will result in clinical benefit.

Commonly used antibacterial and antifungal agents for hospitalised paediatric patients: implications for therapy with an emphasis on clinical pharmacokinetics

Due to normal growth and development, hospitalised paediatric patients with infection require unique consideration of immune function and drug disposition. Specifically, antibacterial and antifungal pharmacokinetics are influenced by volume of distribution, drug binding and elimination, which are a reflection of changing extracellular fluid volume, quantity and quality of plasma proteins, and renal and hepatic function. However, there is a paucity of data in paediatric patients addressing these issues and many empiric treatment practices are based on adult data. The penicillins and cephalosporins continue to be a mainstay of therapy because of their broad spectrum of activity, clinical efficacy and favourable tolerability profile. These antibacterials rapidly reach peak serum concentrations and readily diffuse into body tissues. Good penetration into the cerebrospinal fluid (CSF) has made the third-generation cephalosporins the agents of choice for the treatment of bacterial meningitis. These drugs are excreted primarily by the kidney. The carbapenems are broad-spectrum beta-lactam antibacterials which can potentially replace combination regimens. Vancomycin is a glycopeptide antibacterial with gram-positive activity useful for the treatment of resistant infections, or for those patients allergic to penicillins and cephalosporins. Volume of distribution is affected by age, gender, and bodyweight. It diffuses well across serous membranes and inflamed meninges. Vancomycin is excreted by the kidneys and is not removed by dialysis. The aminoglycosides continue to serve a useful role in the treatment of gram-negative, enterococcal and mycobacterial infections. Their volume of distribution approximates extracellular space. These drugs are also excreted renally and are removed by haemodialysis. Passage across the blood-brain barrier is poor, even in the face of meningeal inflammation. Low pH found in abscess conditions impairs function. Toxicity needs to be considered. Macrolide antibacterials are frequently used in the treatment of respiratory infections. Parenteral erythromycin can cause phlebitis, which limits its use. Parenteral azithromycin is better tolerated but paediatric pharmacokinetic data are lacking. Clindamycin is frequently used when anaerobic infections are suspected. Good oral absorption makes it a good choice for step-down therapy in intra-abdominal and skeletal infections. The use of quinolones in paediatrics has been restricted and most information available is in cystic fibrosis patients. High oral bioavailability is also important for step-down therapy. Amphotericin B has been the cornerstone of antifungal treatment in hospitalised patients. Its metabolism is poorly understood. The half-life increases with time and can be as long as 15 days after prolonged therapy. Oral absorption is poor. The azole antifungals are being used increasingly. Fluconazole is well tolerated, with high bioavailability and good penetration into the CSF. Itraconazole has greater activity against aspergillus, blastomycosis, histoplasmosis and sporotrichosis, although it's pharmacological and toxicity profiles are not as favourable.

Pharmacokinetic optimisation of antibacterial treatment in patients with cystic fibrosis. Current practice and suggestions for future directions

Antibacterials play a central role in the medical management of patients with cystic fibrosis (CF). Administration of adequate dosages of antibacterials results in pronounced beneficial effects on the morbidity and mortality of this patient group. The dosage of the antibacterial that is needed for optimal treatment depends on the individual patient's pharmacokinetics and the pharmacokinetic-pharmacodynamic effect on the micro-organism of relevance in the host. In general, the disposition of antibacterial drugs in patients with CF is not as 'atypical' as once thought. Recent research with adequately matched controls demonstrated that, for a few beta-lactam antibacterials only, a CF-specific increase of the total body clearance seems to exist and that the large volumes of distribution observed are the result of malnutrition and the relative lack of adipose tissue. Pharmacokinetic-pharmacodynamic relationships in patients with CF are less well studied. Apart from the pharmacokinetics, there is a need for optimisation of antibacterial therapy. For the aminoglycosides, pharmacokinetic optimisation based on measured serum drug concentrations is common practice. The Sawchuk-Zaske method based on peak and trough drug concentrations is widely used. A more sophisticated approach is the 'goal-oriented model-based Bayesian adaptive control' method, where integration of mathematically determined optimally (D-optimally) sampled serum drug concentrations and a population model results in the most likely set of individual pharmacokinetic parameter values suitable for further pharmacokinetic optimisation of the therapy. A future development is the integration of changing serum drug concentrations and killing rates of the target micro-organism to a pharmacokinetic-pharmacodynamic surrogate relationship to optimise drug therapy. The latter approach may be extremely useful in deciding on the frequency of aminoglycoside administration as well as the optimal use of the beta-lactam antibacterials and fluoroquinolones.

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.

Optimisation of antibiotic therapy in cystic fibrosis patients. Pharmacokinetic considerations

Antibiotic therapy plays a central role in the medical management of patients with cystic fibrosis. While totally convincing efficacy data are lacking, antibiotics probably have a pronounced beneficial effect on both morbidity and mortality. Much has been learned in the past 20 years about antibiotic use in this population. At the same time, new antimicrobial agents with the potential to treat this condition have become available for use. The pharmacokinetics of a number of antibiotic classes, including beta-lactams, aminoglycosides and quinolones, are altered in this patient population. Increased total body clearance is a common occurrence but is not always changed enough to warrant altered dosages. Nonetheless, in light of altered pharmacokinetics in the cystic fibrosis population, appropriate dosage and monitoring parameters for a number of antibiotics have been determined.

Clinical pharmacokinetics of enzyme inhibitors in antimicrobial chemotherapy

The effectiveness of some antimicrobial agents can be enhanced by using them in combination; such combinations are termed synergistic. Where one compound potentiates the effect of a second drug they may be coformulated. Inhibition of the bacterial degradation of an active antimicrobial is the basis of clavulanate and sulbactam-potentiated penicillin combinations, and inhibition of degradative pathways in the host is the rationale behind imipenem/cilastatin therapy. Trimethoprim/sulphonamide combinations depend on the maintenance of an effective ratio for synergistic action. In order to achieve potentiation the coformulated drugs should have similar pharmacokinetics. Trimethoprim was originally matched with sulphamethoxazole, since these two drugs have similar elimination half-lives, but the significantly poorer penetration of sulphonamides, their greater non-renal clearance, the emergence of resistance, and the adverse reactions attributable to them argue against the rationale that underlies their coformulation. Time-dependent inhibition of bacterial beta-lactamases by clavulanic acid and sulbactam has extended the use of penicillins which are highly susceptible to beta-lactamase inactivation. The beta-lactamase inhibitors must penetrate to the same extent as the penicillin used with them, and be present long enough to effect inhibition; thus, rapid penetration, similar or slower elimination and equivalent volume of distribution are necessary. These requirements are met for amoxycillin/clavulanic acid, ticarcillin/clavulanic acid and ampicillin/sulbactam combinations. Clavulanic acid is absorbed orally and is given with amoxycillin. However, since sulbactam is labile by this route, the combination of sulbactam with ampicillin to form the prodrug sultamicillin has been necessary to enable an oral form to be developed. Imipenem is metabolised by renal brush-border dehydropeptidases, and may cause proximal tubular necrosis. Cilastatin was designed to inhibit this metabolism, which it effectively does, thereby both potentiating the effect of imipenem and avoiding toxicity. Appropriate matching of the kinetics of coformulated drugs is intended to maximise potentiation and minimise the risk of emergent resistance. The kinetics of the above combinations are discussed in the light of these requirements and the effects of age and disease.

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.

Antibiotic pharmacokinetics in cystic fibrosis. Differences and clinical significance

Antibiotics are administered to cystic fibrosis patients for chronic endobronchial infection complicated by frequent exacerbations. Agents active against Staphylococcus aureus, Pseudomonas aeruginosa or both are administered. Serum antibiotic concentrations were measured in cystic fibrosis patients in an effort to optimise antibiotic dose and frequency. This led to the observation that cystic fibrosis subjects had (in general) a larger Vd and increased total body clearance of beta-lactams and aminoglycosides than non-cystic fibrosis subjects. The larger Vd is mainly due to the increased amount of lean body mass per kg bodyweight, although increased tissue binding may also account for part of this. The increased total body clearance of beta-lactams appears to be due to increased renal elimination, particularly tubular secretion. Decreased tubular reabsorption and increased non-renal clearance contribute to the increased total body clearance of metabolised beta-lactams and aminoglycosides. However, the lack of concomitant controls in many studies make these generalisations tentative. The result of the apparent cystic fibrosis-specific differences is lower peak serum antibiotic concentrations, a smaller AUC, and a shorter elimination half-life than non-cystic fibrosis subjects. Since sputum (and bronchial mucosal) concentration is dependent on the peak serum concentration (and AUC), cystic fibrosis subjects require larger doses of most antibiotics more frequently. Newer quinolones may be an exception. Studies comparing the efficacy and safety of larger and more frequent antibiotic doses to conventional therapy are not available. Although it appears logical to mimic serum antibiotic concentrations found in non-cystic fibrosis subjects, the lack of information on the ideal sputum concentration versus time curve should temper our enthusiasm for cystic fibrosis-specific dosage regimens.

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.

Imipenem/cilastatin. A review of its antibacterial activity, pharmacokinetic properties and therapeutic efficacy

Imipenem is the first available semisynthetic thienamycin and is administered intravenously in combination with cilastatin, a renal dipeptidase inhibitor that increases urinary excretion of active drug. In vitro studies have demonstrated that imipenem has an extremely wide spectrum of antibacterial activity against Gram-negative and Gram-positive aerobic and anaerobic bacteria, even against many multiresistant strains of bacteria. It is very potent against species which elaborate beta-lactamases. Imipenem in combination with equal doses of cilastatin has been shown to be generally well tolerated and an effective antimicrobial for the treatment of infections of various body systems. It is likely to be most valuable as empirical treatment of mixed aerobic and anaerobic infections, bacteraemia in non-neutropenic patients and serious hospital-acquired infections.

Ciprofloxacin pharmacokinetics in patients with cystic fibrosis

The pharmacokinetics of ciprofloxacin were studied in cystic fibrosis patients and healthy volunteers following oral administration of 500 mg and 1000 mg. Serum kinetics as well as urinary recovery were monitored. As the body weights of cystic fibrosis patients and the healthy volunteers differed significantly, kinetic parameters were calculated on the basis of a constant relative dose in mg/kg body weight. Neither serum kinetics nor urinary recovery differed significantly between the two groups, as indicated by the serum concentration versus time curves ranging from 1.1 to 1.4 mg X h/l, the elimination half-life of 4.4 to 5.1 h and the 24 h urinary recovery which amounted to 35% to 41% of the dose administered. Serum concentrations were linearly proportional to the doses administered. Sputum concentrations were monitored in cystic fibrosis patients. Again, ciprofloxacin sputum levels were linearly proportional to the doses and were within the same range as serum concentrations. Thus, ciprofloxacin kinetics are not altered in cystic fibrosis patients as compared to healthy volunteers.

Cilastatin does not alter superoxide dismutase activity

Cilastatin inhibits dehydropeptidase-I, a zinc metaloenzyme that metabolizes imipenem. Because zinc stabilizes the mammalian superoxide dismutase, we postulated that cilastatin would also inhibit the dismutase. Cilastatin concentrations at levels threefold higher than those expected in urine, however, did not inhibit the superoxide dismutase activity.