Penetration of ciprofloxacin into the interstitial space of inflamed foot lesions in non-insulin-dependent diabetes mellitus patients

Penetration of Antibiotics into Subcutaneous and Intramuscular Interstitial Fluid: A Meta-Analysis of Microdialysis Studies in Adults

BACKGROUND AND OBJECTIVE

The interstitial fluid of tissues is the effect site for antibiotics targeting extracellular pathogens. Microdialysis studies investigating these concentrations in muscle and subcutaneous tissue have reported notable variability in tissue penetration. This study aimed to comprehensively summarise the existing data on interstitial fluid penetration in these tissues and to identify potential factors influencing antibiotic distribution.

METHODS

A literature review was conducted, focusing on subcutaneous and intramuscular microdialysis studies of antibiotics in both adult healthy volunteers and patients. Random-effect meta-analyses were used to aggregate effect size estimates of tissue penetration. The primary parameter of interest was the unbound penetration ratio, which represents the ratio of the area under the concentration-time curve in interstitial fluid relative to the area under the concentration-time curve in plasma, using unbound concentrations.

RESULTS

In total, 52 reports were incorporated into this analysis. The unbound antibiotic exposure in the interstitial fluid of healthy volunteers was, on average, 22% lower than in plasma. The unbound penetration ratio values were higher after multiple dosing but did not significantly differ between muscle and subcutaneous tissue. Unbound penetration ratio values were lower for acids and bases compared with neutral antibiotics. Neither the molecular weight nor the logP of the antibiotics accounted for the variations in the unbound penetration ratio. Obesity was associated with lower interstitial fluid penetration. Conditions such as sepsis, tissue inflammation and tissue ischaemia were not significantly associated with altered interstitial fluid penetration.

CONCLUSIONS

This study highlights the variability and generally lower exposure of unbound antibiotics in the subcutaneous and intramuscular interstitial fluid compared with exposure in plasma. Future research should focus on understanding the therapeutic relevance of these differences and identify key covariates that may influence them.

Effect of the human endotoxin challenge on tedizolid tissue penetration

The effects of the human endotoxin challenge on tissue pharmacokinetics are unknown. In the present study, we aimed to assess the effect of the endotoxin challenge on interstitial fluid pharmacokinetics of tedizolid in healthy volunteers using intramuscular microdialysis. Eight healthy male subjects were treated with 200 mg of tedizolid phosphate for 6 days. On Day 6, an intravenous bolus of lipopolysaccharide (LPS) (2 ng/kg body weight) was administered. LPS infusion did not affect plasma pharmacokinetics of tedizolid. In contrast, following LPS infusion, median muscle tissue fAUC (0.83 [0.75-1.15] vs. 1.14 [1.11-1.43] mg × h/L, P = .0078) and muscle tissue fC_max (0.15 [0.14-0.19] vs. 0.19 [0.18-0.24] mg/L, P = .0078) were significantly increased by 38% and 24%, respectively. The human endotoxin challenge was associated with increased tissue concentrations of tedizolid, without affecting its plasma concentration-time profile. The human endotoxin challenge combined with microdialysis may be used to investigate the influence of systemic inflammation on tissue pharmacokinetics.

Microdialysis as a tool for antibiotic assessment in patients with diabetic foot: a review

Diabetic foot is a serious late complication frequently caused by infection and ischaemia. Both require prompt and aggressive treatment to avoid lower limb amputation. The effectiveness of peripheral arterial disease therapy can be easily verified using triplex ultrasound, ankle-brachial/toe-brachial index examination, or transcutaneous oxygen pressure. However, the success of infection treatment is difficult to establish in patients with diabetic foot. Intravenous systemic antibiotics are recommended for the treatment of infectious complications in patients with moderate or serious stages of infection. Antibiotic therapy should be initiated promptly and aggressively to achieve sufficient serum and peripheral antibiotic concentrations. Antibiotic serum levels are easily evaluated by pharmacokinetic assessment. However, antibiotic concentrations in peripheral tissues, especially in diabetic foot, are not routinely detectable. This review describes microdialysis techniques that have shown promise in determining antibiotic levels in the surroundings of diabetic foot lesions.

Fluoroquinolone Prescribing for Diabetic Foot Infections following an FDA Drug Safety Communication for Aortic Aneurysm Risk

In 2018, the U.S. Food and Drug Administration (FDA) issued a Drug Safety Communication regarding fluoroquinolone-associated aortic aneurysm. This quasi-experimental study assessed antibiotic prescribing for 198 patients hospitalized with diabetic foot infection. Following the warning, median inpatient fluoroquinolone days of therapy (DOT) decreased from 3 to 0 days (P < 0.001), corresponding to increased beta-lactam DOT and outpatient parenteral antimicrobial therapy enrollment. FDA communications may influence antibiotic selection and transitions of care, representing opportunities for antimicrobial stewardship.

Use of microdialysis for the assessment of fluoroquinolone pharmacokinetics in the clinical practice

Antibacterial drugs, including fluoroquinolones, can exert their therapeutic action only with adequate penetration at the infection site. Multiple factors, such as rate of protein binding, drug liposolubility and organ blood-flow all influence ability of antibiotics to penetrate target tissues. Microdialysis is an in vivo sampling technique that has been successfully applied to measure the distribution of fluoroquinolones in the interstitial fluid of different tissues both in animal studies and clinical setting. Tissue concentrations need to be interpreted within the context of the pathogenesis and causative agents implicated in infections. Integration of microdialysis -derived tissue pharmacokinetics with pharmacodynamic data offers crucial information for correlating exposure with antibacterial effect. This review explores these concepts and provides an overview of tissue concentrations of fluoroquinolones derived from microdialysis studies and explores the therapeutic implications of fluoroquinolone distribution at various target tissues.

New paradigm for rapid achievement of appropriate therapy in special populations: coupling antibiotic dose optimization rapid microbiological methods

INTRODUCTION

Some special patient populations (e.g. critically ill, burns, hematological malignancy, post-major surgery, post-major trauma) have characteristics that lead to higher rates of failure and mortality associated with infection. Choice of effective antibiotics and optimized doses are challenging in these patients that are commonly infected by multidrug-resistant pathogens. Areas covered: A review of the importance of diagnosis and the place of newer microbiological methods (e.g. whole-genome sequencing) to ensure rapid transition from empiric to directed antibiotic therapy is provided. The effects of pathophysiological changes on antibiotic pharmacokinetics are also provided. Expert opinion: Product information dosing regimens do not address the pharmacokinetic alterations that can occur in special patient populations and increase the likelihood of therapeutic failure and the emergence of bacterial resistance. Altered dosing approaches, supplemented with the use of dosing software and therapeutic drug monitoring, may be needed to ensure optimal antibiotic exposure and better therapeutic outcomes in these patients with severe infection. Dose optimization needs to be coupled with advanced microbiological techniques that enable rapid microbiological identification and characterization of resistance mechanism to ensure that maximally effective directed therapy can be chosen.

Factors Affecting Penetration of Ciprofloxacin in Lower Extremity Ischemic Tissues

The aims of this study were to evaluate factors influencing the distribution of ciprofloxacin in tissue of patients suffering from varying degrees of peripheral arterial disease (PAD). Blood and tissue samples were collected from patients undergoing debridement or amputation procedures and the amount of ciprofloxacin in them was determined using high-performance liquid chromatography. All patients were administered a 200-mg dose of intravenous ciprofloxacin prior to the debridement or amputation procedure. Data, including patient gender, age, type of diabetes, presence of neuropathy, medications taken, and severity of PAD were collected. These data were then analyzed to determine factors influencing the concentrations of ciprofloxacin in tissue of the lower limbs. The Kruskal-Wallis test, Spearman correlation, and chi-square test were used to relate covariates and fixed factors with the concentration of ciprofloxacin in tissue. Following bivariate analysis, a 3-predictor regression model was fitted to predict tissue concentrations of ciprofloxacin given information about these predictors. Blood and tissue samples were collected from 50 patients having an average age of 68 years. Thirty-three patients were males and 35 patients suffered from type 2 diabetes. The average number of medications that these patients were taking was 10. The majority of patients (n = 35) were suffering from severe PAD. Tissue concentrations of ciprofloxacin were mainly related to plasma concentrations of ciprofloxacin, number of medications that the patients were taking and severity of PAD.

Antibiotic Tissue Penetration in Diabetic Foot Infections A Review of the Microdialysis Literature and Needs for Future Research

Although many antimicrobial agents display good in vitro activity against the pathogens frequently implicated in diabetic foot infections, effective treatment can be complicated by reduced tissue penetration in this population secondary to peripheral arterial disease and emerging antimicrobial resistance, which can result in clinical failure. Improved characterization of antibiotic tissue pharmacokinetics and penetration ratios in diabetic foot infections is needed. Microdialysis offers advantages over the skin blister and tissue homogenate studies historically used to define antibiotic penetration in skin and soft-tissue infections by defining antibiotic penetration into the interstitial fluid over the entire concentration versus time profile. However, only a select number of agents currently recommended for treating diabetic foot infections have been evaluated using these methods, which are described herein. Better characterization of the tissue penetration of antibiotic agents is needed for the development of methods for maximizing the pharmacodynamic profile of these agents to ultimately improve treatment outcomes for patients with diabetic foot infections.

A comprehensive review on the pharmacokinetics of antibiotics in interstitial fluid spaces in humans: implications on dosing and clinical pharmacokinetic monitoring

The objective of the current review was to provide an updated and comprehensive summary on pharmacokinetic data describing the distribution of antimicrobials into interstitial fluid (ISF) by comparing drug concentration versus time profiles between ISF and blood/plasma in healthy individuals and/or diseased populations. An extensive literature search identified 55 studies detailing 87 individual comparisons. For each antibiotic (antibacterial) (or antibiotic class), we comment on dosing implications based on tissue ISF distribution characteristics and determine the suitability of conducting clinical pharmacokinetic monitoring (CPM) using a previously published scoring algorithm. Using piperacillin as an example, there is evidence supporting different degrees of drug penetration into the ISF of different tissues. A higher dose of piperacillin may be required to achieve an adequate ISF concentration in soft tissue infections. To achieve these higher doses, alternative administration regimens such as intravenous infusions may be utilized. Data also suggest that piperacillin can be categorized as a 'likely suitable' agent for CPM in ISF. Regression analyses of data from the published studies, including protein binding, molecular weight, and predicted partition coefficient (using XlogP3) as dependent variables, indicated that protein binding was the only significant predictor for the extent of drug distribution as determined by ratios of the area under the concentration-time curve between muscle ISF/total plasma (R (2) = 0.65, p < 0.001) and adipose ISF/total plasma (R (2) = 0.48, p < 0.004). Although recurrent limitations (i.e., small sample size, lack of statistical comparisons, lack of steady-state conditions, high individual variability) were identified in many studies, these data are still valuable and allowed us to generate general dosing guidelines and assess the suitability of using ISF for CPM.

Pharmacokinetic/ pharmacodynamic evaluation of anti-infective agents

Pharmacokinetic/pharmacodynamic modeling has become an extremely important tool in evaluating and optimizing anti-infective therapy. By systematically linking the pharmacokinetic and pharmacodynamic properties of the anti-infective agent, it is possible to make educated decisions about the correct drug to be used, correct dosing regimen and to estimate the probability of success with the selected dose regimen. This article gives an overview of the current pharmacokinetic/pharmacodynamic approaches for anti-infective agents and discusses their use in optimizing drug therapy.

Importance of relating efficacy measures to unbound drug concentrations for anti-infective agents

For the optimization of dosing regimens of anti-infective agents, it is imperative to have a good understanding of pharmacokinetics (PK) and pharmacodynamics (PD). Whenever possible, drug efficacy needs to be related to unbound concentrations at the site of action. For anti-infective drugs, the infection site is typically located outside plasma, and a drug must diffuse through capillary membranes to reach its target. Disease- and drug-related factors can contribute to differential tissue distribution. As a result, the assumption that the plasma concentration of drugs represents a suitable surrogate of tissue concentrations may lead to erroneous conclusions. Quantifying drug exposure in tissues represents an opportunity to relate the pharmacologically active concentrations to an observed pharmacodynamic parameter, such as the MIC. Selection of an appropriate specimen to sample and the advantages and limitations of the available sampling techniques require careful consideration. Ultimately, the goal will be to assess the appropriateness of a drug and dosing regimen for a specific pathogen and infection.

Managing diabetic foot infection in India

The burden of diabetic foot complications, in terms of both physical and socioeconomical constraints, poses a heavy challenge both to the patient and the physician, especially in developing countries, where the number of people living with diabetes is increasing at an alarming rate compared with the developed world. In developing countries like India, there are specific causes and risk factors that increase the burden of diabetic foot infections (DFIs), for example, sociocultural risk factors such as barefoot walking, using improper footwear, poor knowledge of foot care practices, lack of adequate and timely access to podiatry services, and poor health care resources. Management of DFI in light of these limitations is quite a challenge to health care professionals. Several techniques and strategies are required to address this problem and should be combined with a multidisciplinary team effort to reduce the burgeoning epidemic of diabetic foot disease. This review is intended to address some of the major aspects of management of DFI in India.

2012 Infectious Diseases Society of America clinical practice guideline for the diagnosis and treatment of diabetic foot infections

Foot infections are a common and serious problem in persons with diabetes. Diabetic foot infections (DFIs) typically begin in a wound, most often a neuropathic ulceration. While all wounds are colonized with microorganisms, the presence of infection is defined by ≥2 classic findings of inflammation or purulence. Infections are then classified into mild (superficial and limited in size and depth), moderate (deeper or more extensive), or severe (accompanied by systemic signs or metabolic perturbations). This classification system, along with a vascular assessment, helps determine which patients should be hospitalized, which may require special imaging procedures or surgical interventions, and which will require amputation. Most DFIs are polymicrobial, with aerobic gram-positive cocci (GPC), and especially staphylococci, the most common causative organisms. Aerobic gram-negative bacilli are frequently copathogens in infections that are chronic or follow antibiotic treatment, and obligate anaerobes may be copathogens in ischemic or necrotic wounds. Wounds without evidence of soft tissue or bone infection do not require antibiotic therapy. For infected wounds, obtain a post-debridement specimen (preferably of tissue) for aerobic and anaerobic culture. Empiric antibiotic therapy can be narrowly targeted at GPC in many acutely infected patients, but those at risk for infection with antibiotic-resistant organisms or with chronic, previously treated, or severe infections usually require broader spectrum regimens. Imaging is helpful in most DFIs; plain radiographs may be sufficient, but magnetic resonance imaging is far more sensitive and specific. Osteomyelitis occurs in many diabetic patients with a foot wound and can be difficult to diagnose (optimally defined by bone culture and histology) and treat (often requiring surgical debridement or resection, and/or prolonged antibiotic therapy). Most DFIs require some surgical intervention, ranging from minor (debridement) to major (resection, amputation). Wounds must also be properly dressed and off-loaded of pressure, and patients need regular follow-up. An ischemic foot may require revascularization, and some nonresponding patients may benefit from selected adjunctive measures. Employing multidisciplinary foot teams improves outcomes. Clinicians and healthcare organizations should attempt to monitor, and thereby improve, their outcomes and processes in caring for DFIs.

Expert opinion on the management of infections in the diabetic foot

This update of the International Working Group on the Diabetic Foot incorporates some information from a related review of diabetic foot osteomyelitis (DFO) and a systematic review of the management of infection of the diabetic foot. The pathophysiology of these infections is now well understood, and there is a validated system for classifying the severity of infections based on their clinical findings. Diagnosing osteomyelitis remains difficult, but several recent publications have clarified the role of clinical, laboratory and imaging tests. Magnetic resonance imaging has emerged as the most accurate means of diagnosing bone infection, but bone biopsy for culture and histopathology remains the criterion standard. Determining the organisms responsible for a diabetic foot infection via culture of appropriately collected tissue specimens enables clinicians to make optimal antibiotic choices based on culture and sensitivity results. In addition to culture-directed antibiotic therapy, most infections require some surgical intervention, ranging from minor debridement to major resection, amputation or revascularization. Clinicians must also provide proper wound care to ensure healing of the wound. Various adjunctive therapies may benefit some patients, but the data supporting them are weak. If properly treated, most diabetic foot infections can be cured. Providers practising in developing countries, and their patients, face especially challenging situations.

Blood, tissue, and intracellular concentrations of erythromycin and its metabolite anhydroerythromycin during and after therapy

For macrolides, clinical activity but also the development of bacterial resistance has been attributed to prolonged therapeutic and subtherapeutic concentrations. Although erythromycin is a long-established antimicrobial, concomitant determination of the pharmacokinetics of erythromycin and its metabolites in different compartments is limited. To better characterize the pharmacokinetics of erythromycin and its anhydrometabolite (anhydroerythromycin [AHE]) in different compartments during and after the end of treatment with 500 mg of erythromycin four times daily, concentration-time profiles were determined in plasma, interstitial space of muscle and subcutaneous adipose tissue, and white blood cells (WBCs) at days 1 and 3 of treatment and 2 and 7 days after end of therapy. In WBCs, concentrations of erythromycin exceeded those in plasma approximately 40-fold, while free concentrations in plasma and tissue were comparable. The observed delay of peak concentrations in tissue might be caused by fast initial cellular uptake. Two days after the end of treatment, subinhibitory concentrations were observed in plasma and interstitial space of both soft tissues, while 7 days after the end of treatment, erythromycin was not detectable in any compartment. This relatively short period of subinhibitory concentrations may be advantageous compared to other macrolides. The ratio of erythromycin over AHE on day 1 was highest in plasma (2.81 ± 3.45) and lowest in WBCs (0.27 ± 0.22). While the ratio remained constant between single dose and steady state, after the end of treatment the concentration of AHE declined more slowly than that of the parent compound, indicating the importance of the metabolite for the prolonged drug interaction of erythromycin.

The third-generation P-glycoprotein inhibitor tariquidar may overcome bacterial multidrug resistance by increasing intracellular drug concentration

OBJECTIVES

The use of efflux pump inhibitors may be a powerful strategy to overcome transporter-mediated bacterial multidrug resistance. In the present study, we set out to investigate the potency of tariquidar, a third-generation P-glycoprotein inhibitor in clinical development, for overcoming bacterial resistance towards ciprofloxacin.

METHODS

Staphylococcus aureus 29213 (SA29213) and S. aureus 1199B (SA1199B), which overexpresses the multidrug transporter NorA, as well as Pseudomonas aeruginosa 27853 and Stenotrophomonas maltophilia BAA-85, which expresses SmeDEF, were exposed to ciprofloxacin in the presence and absence of tariquidar or, for comparative reasons, elacridar. Activity of both P-glycoprotein inhibitors was evaluated by determination of MICs and time-kill curves, and by quantification of uptake of ciprofloxacin into bacterial cells.

RESULTS

Activity of tariquidar and elacridar was comparable for S. aureus strains, and both dose-dependently increased susceptibility towards ciprofloxacin. Highest effects were observed for SA1199B, where the addition of tariquidar resulted in a 10-fold reduction of the ciprofloxacin MIC, while no effect was observed for P. aeruginosa. For S. maltophilia, elacridar but not tariquidar improved susceptibility. Uptake of [14C]ciprofloxacin and modification of susceptibility showed significant correlations (r=0.89, P<0.0001). Tariquidar had no intrinsic activity against any strain tested.

CONCLUSIONS

We conclude that tariquidar has potent inhibitory effect against certain bacterial efflux pumps in vitro. Their high activity at clinically achievable concentrations might yield this class of drugs promising for future applications in infectious diseases.

Antimicrobial chemotherapy and lung microdialysis: a review

Pneumonia is a form of lung infection that may be caused by various micro-organisms. The predominant site of infection in pneumonia is debatable. Advances in the fields of diagnostic and therapeutic medicine have had a less than optimal effect on the outcome of pneumonia and one of the many causes is likely to be inadequate antimicrobial concentrations at the site of infection in lung tissue. Traditional antimicrobial therapy guidelines are based on indirect modelling from blood antimicrobial levels. However, studies both in humans and animals have shown the fallacy of this concept in various tissues. Many different methods have been employed to study lung tissue antimicrobial levels with limited success, and each has limitations that diminish their utility. An emerging technique being used to study the pharmacokinetics of antimicrobial agents in lung tissue is microdialysis. Development of microdialysis catheters, along with improvement in analytical techniques, has improved the accuracy of the data. Unfortunately, very few studies have reported the use of microdialysis in lung tissue, and even fewer antimicrobial classes have been studied. These studies generally suggest that this technique is a safe and effective way of assessing the pharmacokinetics of antimicrobial agents in lung tissue. Further descriptive studies need to be conducted to study the pharmacokinetics and pharmacodynamics of different antimicrobial classes in lung tissue. Data emanating from these studies could inform decisions for appropriate dosing schedules of antimicrobial agents in pneumonia.

Peripheral distribution of amoxicillin in sheep and influence of local inflammation

The pharmacokinetics of amoxicillin (AMX) in blood serum (SBS) and tissue cage fluid (TCF) was studied in sheep. Four tissue cages, prepared from silicone rubber tubing, were subcutaneously inserted in the neck area (two on each side) of the experimental animals and AMX was administered both intravenously (IV) and intramuscularly (IM) at the dose rate of 15mg/kg bodyweight. The impact of local inflammation on AMX distribution in TCF was studied after intra-cavity injection of a lambda carrageenan solution in one of the two tissue cages used after each administration. In contrast to the three-compartment AMX disposition after IV injection, two-compartment, absorption-limited pharmacokinetics was observed after IM administration. Non-inflamed and inflamed TCF data revealed, in all cases, the attainment of low, but prolonged concentrations and absence of an inflammation-induced effect on AMX penetration into and elimination from TCF.

Piperacillin penetration into tissue of critically ill patients with sepsis--bolus versus continuous administration?

OBJECTIVE

To describe a pharmacokinetic model of piperacillin concentrations in plasma and subcutaneous tissue when administered by bolus dosing and continuous infusion in critically ill patients with sepsis on days 1 and 2 of antibiotic therapy and to compare results against previous results for piperacillin from a cohort of patients with septic shock.

DESIGN

Prospective randomized controlled trial.

SETTING

Eighteen-bed intensive care unit at 918-bed tertiary referral hospital.

PATIENTS

Thirteen critically ill adult patients with known or suspected sepsis in whom the treating physician deemed piperacillin-tazobactam appropriate therapy were conveniently sampled.

INTERVENTIONS

Patients were randomized to receive different daily doses of piperacillin-tazobactam by bolus dosing or continuous infusion (continuous infusion--six patients; bolus dosing--seven patients). Serial plasma and tissue concentrations were determined on days 1 and 2 of treatment. Tissue concentrations of piperacillin were determined using a subcutaneously inserted microdialysis catheter. Separate pharmacokinetic models were developed for both bolus and continuous dosing.

MEASUREMENTS AND MAIN RESULTS

This is the first known article to report concurrent plasma and subcutaneous tissue concentrations of a beta-lactam antibiotic administered by bolus and continuous dosing in critically ill patients with sepsis. With a 25% lower piperacillin dose administered to the continuous infusion group, the infusion group had statistically significantly higher median plasma concentrations than the bolus group on day 2 (16.6 vs. 4.9 mg/L; p = 0.007). There was a trend to higher median plasma concentrations on day 1 in the bolus dosing group (8.9 vs. 4.9 mg/L; p = 0.078). Median tissue concentrations were not statistically different on day 1 (infusion group 2.4 mg/L vs. bolus group 2.2 mg/L; p = 0.48) and day 2 (infusion group 5.2 mg/L vs. bolus group 0.8 mg/L; p = 0.45). A two-compartment pharmacokinetic model was found to describe the data best. Tissue pharmacodynamic targets were achieved more successfully with infusion dosing.

CONCLUSIONS

Patients with sepsis do not seem to have the same level of impairment of tissue distribution as described for patients with septic shock. A 25% lower dose of piperacillin administered by continuous infusion seems to maintain higher trough concentrations compared with standard bolus dosing. It is likely that the clinical advantages of continuous infusion are most likely to be evident when treating pathogens with high minimum inhibitory concentration, although without therapeutic drug monitoring and subsequent dose adjustment, infusions may never achieve target concentrations of organisms with very high minimum inhibitory concentrations in a small number of patients.

Treating diabetic foot infections with sequential intravenous to oral moxifloxacin compared with piperacillin–tazobactam/amoxicillin–clavulanate

OBJECTIVES

Complicated skin and skin structure infections (cSSSIs), including diabetic foot infections (DFIs), are often polymicrobial, requiring combination or broad-spectrum therapy. Moxifloxacin, a broad-spectrum fluoroquinolone, is approved for cSSSI and can be administered by either intravenous (iv) or oral routes. To assess the efficacy of moxifloxacin for treating DFIs, we analysed a subset of patients with these infections who were enrolled in a prospective, double-blind study that compared the efficacy of moxifloxacin with piperacillin-tazobactam and amoxicillin-clavulanate.

METHODS

Patients>or=18 years of age with a DFI requiring initial iv therapy were randomized to either moxifloxacin (400 mg/day) or piperacillin-tazobactam (3.0/0.375 g every 6 h) for at least 3 days followed by moxifloxacin (400 mg/day orally) or amoxicillin-clavulanate (800 mg every 12 h orally), if appropriate, for 7-14 days. DFI was usually defined as any foot infection plus a history of diabetes. Our primary efficacy outcome was the clinical response of the infection at test-of-cure (TOC), 10-42 days post-therapy.

RESULTS

Among 617 patients enrolled in the original study, 78 with DFIs were evaluable for treatment efficacy. Clinical cure rates at TOC were similar for moxifloxacin and piperacillin-tazobactam/amoxicillin-clavulanate (68% versus 61%) for patients with investigator-defined infection (P=0.54). Overall pathogen eradication rates in the microbiologically-valid population were 69% versus 66% for moxifloxacin and comparator, respectively (P=1.00).

CONCLUSIONS

Intravenous+/-oral moxifloxacin was as effective as iv piperacillin-tazobactam+/-amoxicillin-clavulanate in treating moderate-to-severe DFIs. Moxifloxacin may have potential as a monotherapy regimen for DFIs.

Clinical management of diabetic foot infection: diagnostics, therapeutics and the future

Diabetic foot infection accounts for a substantial global burden of morbidity, psychosocial disruption and economic cost. Recommendations for best practice are continuously evolving in parallel with improvements in imaging modalities, development and clinical use of new antimicrobial agents and data surrounding novel adjunctive strategies. We discuss this complex group of infections with a particular emphasis on medical management of osteomyelitis, while also highlighting the importance of a broad multidisciplinary approach to eradicating infection.

A simple isocratic HPLC assay to determine linezolid concentrations in different biomatrices for in vivo and in vitro studies

BACKGROUND

Linezolid is an important therapeutic option for the treatment of infections caused by multiresistant Gram-positive bacteria such as vancomycin-resistant Enterococci (VRE) and methicillin-resistant Staphylococcus aureus (MRSA). However, the clinical benefit of linezolid is threatened by the emergence of resistant strains of MRSA and VRE reported in North America and Europe. For effective antimicrobial treatment, it is extremely important to have exact knowledge of drug concentrations at the site of action.

METHODS

A simple HPLC method for the rapid and precise determination of linezolid in different biomatrices (e.g., plasma, soft tissue, bone, dialysis fluid and used microbiological broth) was developed and validated. Proteins were precipitated with acetonitrile and separation was performed on a reversed-phase C8 column with a mobile phase consisting of water/acetonitrile (80:20, v/v). UV detection was performed at 251 nm.

RESULTS

This method has a lower limit of quantification of 0.3 microg/mL and a linear calibration range of 0.5-40 microg/mL. The method showed excellent reproducibility, with an inter- and intra-day assay precision of <5% (% relative standard deviation), as well as excellent accuracy, with inter- and intra-day assay accuracy ranging from 100.6% to 103.2%. Stability up to 6 months in water and plasma was proven. Quantitative recovery was possible after up to three freeze thaw cycles.

CONCLUSIONS

The method is useful in the acquisition of in vivo and in vitro data. It is simple, flexible, specific, precise and reproducible, as well as of adequate sensitivity for clinical use.

A post hoc subgroup analysis of meropenem versus imipenem/cilastatin in a multicenter, double-blind, randomized study of complicated skin and skin-structure infections in patients with diabetes mellitus

BACKGROUND

In a multicenter, international, double-blind, randomized clinical trial involving hospitalized patients with complicated skin and skin-structure infections (cSSSIs), meropenem and imipenem/cilastatin (both administered 500 mg intravenously every 8 hours) were not significantly different in their efficacy and safety profiles.

OBJECTIVE

The objective of the post hoc subgroup analysis discussed in the current article was to report the efficacy and tolerability of meropenem and imipenem/cilastatin for the treatment of cSSSIs in patients with or without underlying diabetes mellitus (DM).

METHODS

Hospitalized patients aged > or =13 years with evidence of cSSSIs were eligible for inclusion. Patients were randomized to receive meropenem or imipenem/cilastatin, each 500 mg intravenously every 8 hours, for at least 3 days and up to a maximum of 14 days. Patients were analyzed according to the presence or absence of DM and by the pathogen(s) isolated from wound cultures at baseline, end of N treatment, and test-of-cure visits. The primary efficacy end point was clinical outcome at the posttreatment follow-up (test-of-cure) visit in the clinically evaluable and modified intent-to-treat (intent-to-treat [ITT] subjects who met all eligibility criteria) populations; this was defined as 7 to 14 days after final administration of antibiotics. The secondary efficacy end points included clinical response at the test-of-cure visit in the ITT population (ie, those who received >1 dose of study drug) and at the end of N treatment visit in the clinically evaluable and fully evaluable populations. At baseline, the end of N treatment, and the test-of-cure visits, specimens were obtained from the most extensive site of skin and skin-structure infection and were cultured for bacteria. Adverse events were monitored daily during treatment and for 30 days after the completion of all antibiotic treatment.

RESULTS

Of the 1076 patients enrolled in the original study, 398 had DM. The mean ages of patients with and without DM were 55 and 45 years, respectively; 17.3% of patients with DM and 6.1% of patients without DM had impaired renal function at study entry. Complex abscess was the most common infection diagnosis in both groups (patients with DM, 30.0%; patients without DM, 48.8%). The other top infections per group (patients with and without DM, respectively) were as follows: cellulitis, 24.6% and 12.4%; and ischemic/diabetic ulcers, 20.9% and 1.9%. Gram-negative aerobic and anaerobic pathogens accounted for >40% of bacterial isolates from both groups, with polymicrobial infections reported in 44.2% of patients with DM and 34.0% of patients without DM. In the clinically evaluable population, the satisfactory clinical response rate was 85.6% for patients with DM receiving meropenem and 72.4% for those receiving imipenem/cilastatin; for patients without DM, those rates were 86.6% and 89.0%, respectively. Meropenem and imipenem/cilastatin were generally well tolerated. Reported adverse events were similar between groups.

CONCLUSION

This subgroup analysis found that 500 mg every 8 hours intravenously of meropenem or imipenem/cilastatin appeared efficacious and well tolerated for the treatment of cSSSIs among these patients with and without DM.

Diagnosis and treatment of diabetic foot infections

EXECUTIVE SUMMARY: 1. Foot infections in patients with diabetes cause substantial morbidity and frequent visits to health care professionals and may lead to amputation of a lower extremity. 2. Diabetic foot infections require attention to local (foot) and systemic (metabolic) issues and coordinated management, preferably by a multidisciplinary foot-care team (A-II). The team managing these infections should include, or have ready access to, an infectious diseases specialist or a medical microbiologist (B-II). 3. The major predisposing factor to these infections is foot ulceration, which is usually related to peripheral neuropathy. Peripheral vascular disease and various immunological disturbances play a secondary role. 4. Aerobic Gram-positive cocci (especially Staphylococcus aureus) are the predominant pathogens in diabetic foot infections. Patients who have chronic wounds or who have recently received antibiotic therapy may also be infected with Gram-negative rods, and those with foot ischemia or gangrene may have obligate anaerobic pathogens. 5. Wound infections must be diagnosed clinically on the basis of local (and occasionally systemic) signs and symptoms of inflammation. Laboratory (including microbiological) investigations are of limited use for diagnosing infection, except in cases of osteomyelitis (B-II). 6. Send appropriately obtained specimens for culture before starting empirical antibiotic therapy in all cases of infection, except perhaps those that are mild and previously untreated (B-III). Tissue specimens obtained by biopsy, ulcer curettage, or aspiration are preferable to wound swab specimens (A-I). 7. Imaging studies may help diagnose or better define deep, soft-tissue purulent collections and are usually needed to detect pathological findings in bone. Plain radiography may be adequate in many cases, but MRI (in preference to isotope scanning) is more sensitive and specific, especially for detection of soft-tissue lesions (A-I). 8. Infections should be categorized by their severity on the basis of readily assessable clinical and laboratory features (B-II). Most important among these are the specific tissues involved, the adequacy of arterial perfusion, and the presence of systemic toxicity or metabolic instability. Categorization helps determine the degree of risk to the patient and the limb and, thus, the urgency and venue of management. 9. Available evidence does not support treating clinically uninfected ulcers with antibiotic therapy (D-III). Antibiotic therapy is necessary for virtually all infected wounds, but it is often insufficient without appropriate wound care. 10. Select an empirical antibiotic regimen on the basis of the severity of the infection and the likely etiologic agent(s) (B-II). Therapy aimed solely at aerobic Gram-positive cocci may be sufficient for mild-to-moderate infections in patients who have not recently received antibiotic therapy (A-II). Broad-spectrum empirical therapy is not routinely required but is indicated for severe infections, pending culture results and antibiotic susceptibility data (B-III). Take into consideration any recent antibiotic therapy and local antibiotic susceptibility data, especially the prevalence of methicillin-resistant S. aureus (MRSA) or other resistant organisms. Definitive therapy should be based on both the culture results and susceptibility data and the clinical response to the empirical regimen (C-III). 11. There is only limited evidence with which to make informed choices among the various topical, oral, and parenteral antibiotic agents. Virtually all severe and some moderate infections require parenteral therapy, at least initially (C-III). Highly bioavailable oral antibiotics can be used in most mild and in many moderate infections, including some cases of osteomyelitis (A-II). Topical therapy may be used for some mild superficial infections (B-I). 12. Continue antibiotic therapy until there is evidence that the infection has resolved but not necessarily until a wound has healed. Suggestions for the duration of antibiotic therapy are as follows: for mild infections, 12 weeks usually suffices, but some require an additional 12 weeks; for moderate and severe infections, usually 24 weeks is sufficient, depending on the structures involved, the adequacy of debridement, the type of soft-tissue wound cover, and wound vascularity (A-II); and for osteomyelitis, generally at least 46 weeks is required, but a shorter duration is sufficient if the entire infected bone is removed, and probably a longer duration is needed if infected bone remains (B-II). 13. If an infection in a clinically stable patient fails to respond to 1 antibiotic courses, consider discontinuing all antimicrobials and, after a few days, obtaining optimal culture specimens (C-III). 14. Seek surgical consultation and, when needed, intervention for infections accompanied by a deep abscess, extensive bone or joint involvement, crepitus, substantial necrosis or gangrene, or necrotizing fasciitis (A-II). Evaluating the limb's arterial supply and revascularizing when indicated are particularly important. Surgeons with experience and interest in the field should be recruited by the foot-care team, if possible. 15. Providing optimal wound care, in addition to appropriate antibiotic treatment of the infection, is crucial for healing (A-I). This includes proper wound cleansing, debridement of any callus and necrotic tissue, and, especially, off-loading of pressure. There is insufficient evidence to recommend use of a specific wound dressing or any type of wound healing agents or products for infected foot wounds. 16. Patients with infected wounds require early and careful follow-up observation to ensure that the selected medical and surgical treatment regimens have been appropriate and effective (B-III). 17. Studies have not adequately defined the role of most adjunctive therapies for diabetic foot infections, but systematic reviews suggest that granulocyte colony-stimulating factors and systemic hyperbaric oxygen therapy may help prevent amputations (B-I). These treatments may be useful for severe infections or for those that have not adequately responded to therapy, despite correcting for all amenable local and systemic adverse factors. 18. Spread of infection to bone (osteitis or osteomyelitis) may be difficult to distinguish from noninfectious osteoarthropathy. Clinical examination and imaging tests may suffice, but bone biopsy is valuable for establishing the diagnosis of osteomyelitis, for defining the pathogenic organism(s), and for determining the antibiotic susceptibilities of such organisms (B-II). 19. Although this field has matured, further research is much needed. The committee especially recommends that adequately powered prospective studies be undertaken to elucidate and validate systems for classifying infection, diagnosing osteomyelitis, defining optimal antibiotic regimens in various situations, and clarifying the role of surgery in treating osteomyelitis (A-III).

Impaired target site penetration of vancomycin in diabetic patients following cardiac surgery

Soft tissue infections constitute a serious complication following surgery in diabetic patients and frequently require the administration of vancomycin. However, despite antibiotic treatment, mortality of patients with postoperative infections remains high and might be related to an impaired penetration of anti-infective agents to target tissues. Therefore, the present study was designed to measure vancomycin tissue concentrations in six diabetic and six nondiabetic patients after cardiac surgery. Vancomycin was administered as a continuous intravenous infusion at an infusion rate of 80 to 120 mg/h. Vancomycin concentrations in soft tissues and plasma were measured in all patients during steady state as "therapeutic window" concentrations in plasma by microdialysis on day 8+/-4 after initiation of vancomycin treatment. Vancomycin tissue concentrations in diabetic patients were significantly lower than in nondiabetics (3.7 mg/liter versus 11.9 mg/liter; P=0.002). The median vancomycintissue/vancomycinplasma concentration ratio was 0.1 in diabetic patients and 0.3 in nondiabetics (P=0.002). Our study demonstrated that vancomycin penetration into target tissues is substantially impaired in diabetic patients versus nondiabetics. Insufficient tissue concentrations could therefore possibly contribute to failure of antibiotic treatment and the development of antimicrobial resistance in diabetic patients.

Penetration of piperacillin and tazobactam into inflamed soft tissue of patients with diabetic foot infection

We investigated the pharmacokinetics of piperacillin and tazobactam in the extracellular space fluid of inflamed soft tissues of six patients with diabetic foot infection using in vivo microdialysis and found similar penetration for piperacillin but not for tazobactam into inflamed and noninflamed soft tissue.

Increase of microcirculatory blood flow enhances penetration of ciprofloxacin into soft tissue

The present study addressed the effect of microcirculatory blood flow on the ability of ciprofloxacin to penetrate soft tissues. Twelve healthy male volunteers were enrolled in an analyst-blinded, clinical pharmacokinetic study. A single intravenous dose of 200 mg of ciprofloxacin was administered over a period of approximately 20 min. The concentrations of ciprofloxacin were measured in plasma and in the warmed and contralateral nonwarmed lower extremities. The microdialysis technique was used for the assessment of unbound ciprofloxacin concentrations in subcutaneous adipose tissue. Microcirculatory blood flow was measured by use of laser Doppler flowmetry. Warming of the extremity resulted in an increase of microcirculatory blood flow by approximately three- to fourfold compared to that at the baseline (P < 0.05) in subcutaneous adipose tissue. The ratio of the maximum concentration (C(max)) of ciprofloxacin for the warmed thigh to the C(max) for the nonwarmed thigh was 2.10 +/- 0.90 (mean +/- standard deviation; P < 0.05). A combined in vivo pharmacokinetic (PK)-in vitro pharmacodynamic (PD) simulation based on tissue concentration data indicated that killing of Pseudomonas aeruginosa (ATCC 27853 and two clinical isolates) was more effective by about 2 log(10) CFU/ml under the warmed conditions than under the nonwarmed conditions (P < 0.05). The improvement of microcirculatory blood flow due to the warming of the extremity was paralleled by an increased ability of ciprofloxacin to penetrate soft tissue. Subsequent PK-PD simulations based on tissue PK data indicated that this increase in tissue penetration was linked to an improved antimicrobial effect at the target site.

Plasma concentrations might lead to overestimation of target site activity of piperacillin in patients with sepsis

OBJECTIVES

Pharmacokinetic (PK)/pharmacodynamic (PD) models have become increasingly important in optimizing antimicrobial therapy. This approach is highly recommended by regulatory authorities intending to force the evaluation of antimicrobial action at the site of infection.

METHODS

Clinical isolates of Pseudomonas aeruginosa and Staphylococcus aureus with MICs of 4, 8 and 16 mg/L for piperacillin were used in an in vivo PK/in vitro PD model. Bacteria were exposed in vitro to the concentration-versus-time profiles of piperacillin in plasma and subcutaneous adipose tissue measured in vivo in septic patients. Samples were withdrawn at defined intervals and the numbers of bacteria per mL were counted and plotted against time.

RESULTS

Piperacillin levels determined in plasma were able to effectively inhibit bacterial growth of all bacterial strains used in the present study (MIC ranged from 4-16 mg/L). In contrast, concentration-versus-time profiles of subcutaneous adipose tissue were effective in killing isolates with MICs of 4 and 8 mg/L only, while bacterial growth of S. aureus and P. aeruginosa with MICs of 16 mg/L was not inhibited.

CONCLUSIONS

Bacteria with MICs < 16 mg/L were effectively inhibited in subcutaneous adipose tissue in patients with sepsis. The prediction of microbiological outcome based on concentrations of piperacillin in plasma resulted in a marked overestimation of antimicrobial activity at the site of infection.

Penetration of ciprofloxacin and its desethylenemetabolite into skin in humans after a single oral dose of the parent drug assessed by cutaneous microdialysis

OBJECTIVE

To measure the concentration of ciprofloxacin and its desethylenemetabolite in plasma and cutaneous microdialysates and to compare ciprofloxacin penetration into cutaneous microdialysates against theoretically predicted penetration in a peripheral compartment.

METHOD

A single oral dose of 0.5 g of the parent drug was administered to 10 healthy male volunteers. Microdialysis probes with 2 kDa molecular weight cut-off were inserted intradermally and were perfused with Ringer solution up to 8 h after drug ingestion. Drug and metabolite concentrations were measured by high performance liquid chromatography.

RESULTS

Mean maximum concentrations of ciprofloxacin in plasma, cutaneous microdialysates and theoretical peripheral compartment were 7.01+/-1.69, 2.95+/-0.64 and 3.37+/-0.60 micromol/L, respectively, and were achieved after about 2.0+/-0.6, 2.4+/-0.9 and 4.8+/-0.9 h. The extent of penetration into cutaneous microdialysates and theoretical peripheral compartment relative to plasma were 0.550+/-0.150 and 0.788+/-0.131, respectively, and differed significantly. Similarly, time to maximum concentration as well as area under the concentration-time curve in these compartments also differed significantly unlike the maximum concentration.

CONCLUSION

Microdialysis permits the evaluation of the penetration of drug and its metabolites into target tissues. Such evaluation is helpful to optimize treatment strategies. After a single 0.5 g oral dose, ciprofloxacin penetrated into skin and achieved concentrations above the minimum inhibitory concentrations for susceptible pathogens, recommended by the National Committee for Clinical Laboratory Standards (NCCLS).

Antimicrobial interventions for the management of diabetic foot infections

Foot infections are the most common cause of hospitalisations and amputations in diabetic patients. They occur after skin ulcers or trauma in patients with peripheral neuropathy, sometimes together with vascular disease. Narrow-spectrum antibiotic agents should be prescribed for minor recent infections, and broader-spectrum agents for severe or chronic infections. When indicated, antibiotic therapy should be started early and be tailored to the individual patient. Diabetic foot osteomyelitis is a particularly controversial condition, especially regarding the need for reliable cultures, the type and duration of treatment, and the role of surgery. Recent data indicates that a medical approach might be effective and could reduce foot amputations among diabetic patients. Interdisciplinary cooperation with infectious disease specialists and orthopaedic surgeons should be considered in such situations.

Microdialysis

Microdialysis is a probe-based sampling method, which, if linked to analytical devices, allows for the measurement of drug concentration profiles in selected tissues. During the last two decades, microdialysis has become increasingly popular for preclinical and clinical pharmacokinetic studies. The advantage of in vivo microdialysis over traditional methods relates to its ability to continuously sample the unbound drug fraction in the interstitial space fluid (ISF). This is of particular importance because the ISF may be regarded as the actual target compartment for many drugs, e.g. antimicrobial agents or other drugs mediating their action through surface receptors. In contrast, plasma concentrations are increasingly recognised as inadequately predicting tissue drug concentrations and therapeutic success in many patient populations. Thus, the minimally invasive microdialysis technique has evolved into an important tool for the direct assessment of drug concentrations at the site of drug delivery in virtually all tissues. In particular, concentrations of transdermally applied drugs, neurotransmitters, antibacterials, cytotoxic agents, hormones, large molecules such as cytokines and proteins, and many other compounds were described by means of microdialysis. The combined use of microdialysis with non-invasive imaging methods such as positron emission tomography and single photon emission tomography opened the window to exactly explore and describe the fate and pharmacokinetics of a drug in the body. Linking pharmacokinetic data from the ISF to pharmacodynamic information appears to be a straightforward approach to predicting drug action and therapeutic success, and may be used for decision making for adequate drug administration and dosing regimens. Hence, microdialysis is nowadays used in clinical studies to test new drug candidates that are in the pharmaceutical industry drug development pipeline.

[18F]Ciprofloxacin, a new positron emission tomography tracer for noninvasive assessment of the tissue distribution and pharmacokinetics of ciprofloxacin in humans

The biodistribution and pharmacokinetics of the fluorine-18-labeled fluoroquinolone antibiotic [(18)F]ciprofloxacin in tissue were studied noninvasively in humans by means of positron emission tomography (PET). Special attention was paid to characterizing the distribution of [(18)F]ciprofloxacin to select target tissues. Healthy volunteers (n = 12) were orally pretreated for 5 days with therapeutic doses of unlabeled ciprofloxacin. On day 6, subjects received a tracer dose (mean injected amount, 700 +/- 55 MBq, which contained about 0.6 mg of unlabeled ciprofloxacin) of [(18)F]ciprofloxacin as an intravenous bolus. Thereafter, PET imaging and venous blood sampling were initiated. Time-radioactivity curves were measured for liver, kidney, lung, heart, spleen, skeletal muscle, and brain tissues for up to 6 h after radiotracer administration. The first application of [(18)F]ciprofloxacin in humans has demonstrated the safety and utility of the newly developed radiotracer for pharmacokinetic PET imaging of the tissue ciprofloxacin distribution. Two different tissue compartments of radiotracer distribution could be identified. The first compartment including the kidney, heart, and spleen, from which the radiotracer was washed out relatively quickly (half-lives [t(1/2)s], 68, 57, and 106 min, respectively). The second compartment comprised liver, muscle, and lung tissue, which displayed prolonged radiotracer retention (t(1/2), >130 min). The highest concentrations of radioactivity were measured in the liver and kidney, the main organs of excretion (standardized uptake values [SUVs], 4.9 +/- 1.0 and 9.9 +/- 4.4, respectively). The brain radioactivity concentrations were very low (<1 kBq. g(-1)) and could therefore not be quantified. Transformation of SUVs into absolute concentrations (in micrograms per milliliter) allowed us to relate the concentrations at the target site to the susceptibilities of bacterial pathogens. In this way, the frequent use of ciprofloxacin for the treatment of a variety of infections could be corroborated.

Diagnosis and treatment of diabetic foot infections

Diabetic foot infections frequently cause morbidity, hospitalization, and amputations. Gram-positive cocci, especially staphylococci and also streptococci, are the predominant pathogens. Chronic or previously treated wounds often yield several microbes on culture, including gram-negative bacilli and anaerobes. Optimal culture specimens are wound tissue taken after debridement. Infection of a wound is defined clinically by the presence of purulent discharge or inflammation; systemic signs and symptoms are often lacking. Only infected wounds require antibiotic therapy, and the agents, route, and duration are predicated on the severity of infection. Mild to moderate infections can usually be treated in the outpatient setting with oral agents; severe infections require hospitalization and parenteral therapy. Empirical therapy must cover gram-positive cocci and should be broad spectrum for severe infections. Definitive therapy depends on culture results and the clinical response. Bone infection is particularly difficult to treat and often requires surgery. Several adjuvant agents may be beneficial in some cases.

Tissue pharmacokinetics of levofloxacin in human soft tissue infections

AIMS

The present study addressed the ability of levofloxacin to penetrate into subcutaneous adipose tissues in patients with soft tissue infection.

METHODS

Tissue concentrations of levofloxacin in inflamed and healthy subcutaneous adipose tissue were measured in six patients by microdialysis after administration of a single intravenous dose of 500 mg. Levofloxacin was assayed by high-performance liquid chromatography.

RESULTS

The mean concentration vs time profile of free levofloxacin in plasma was identical to that in inflamed and healthy tissues. The ratios of the mean area under the free levofloxacin concentration vs time curve from 0 to 10 h (AUC(0,10 h)) in tissue to that in plasma were 1.2 +/- 1.0 for inflamed and 1.1 +/- 0.6 for healthy subcutaneous adipose tissue (mean +/- SD). The mean difference in the ratio of the AUC(tissue) : AUC(plasma) for inflamed and healthy tissue was 0.09 (95% confidence interval -0.58, 0.759, P > 0.05). Interindividual variability in tissue penetration was high, as indicated by a coefficient of variation of approximately 82% for AUC(tissue) : AUC(plasma) ratios.

CONCLUSIONS

The penetration of levofloxacin into tissue appears to be unaffected by local inflammation. Our plasma and tissue data suggest that an intravenous dose of 500 mg levofloxacin provides effective antibacterial concentrations at the target site. However, in treatment resistant patients, tissue concentrations may be sub-therapeutic.

Antimicrobial tissue concentrations

The clinical outcome of anti-infective treatment is determined by both PK and PD properties of the antibiotic. Only the free tissue concentrations of antibiotics at the target site, which are usually lower than the total plasma concentrations, are responsible for therapeutic effect. The free antibiotic concentrations at the site of action are a more appropriate PK input value for PK-PD analysis. The unbound tissue concentrations can be measured directly by microdialysis. Using plasma concentrations overestimates the target site concentrations and its clinical efficacy. The optimal dosing regimens of antibiotics have an impact on patients' outcome and cost of therapy, and reduce the emergence of resistance.

Synthesis of fluorine-18-labeled ciprofloxacin for PET studies in humans

Ciprofloxacin (1-cyclopropyl-6-fluoro-1,4-dihydro-4-oxo-7-(1-piperazinyl)-quinoline-3-carboxylic acid), a widely-prescribed antibiotic, was labeled with fluorine-18 with the aim to perform positron emission tomography studies in humans for pharmacokinetic measurements. Due to a lack of chemical activation of ciprofloxacin for a direct nucleophilic exchange reaction a novel two-step synthetic approach, which employed an activated 6-fluoro-7-chloro substituted precursor molecule, was developed. The radiosynthesis yielded, starting from 52.5 +/- 11.3 GBq of [(18)F]fluoride, 1.3 +/- 0.6 GBq (n = 13) [(18)F]ciprofloxacin ready for intravenous administration in about 130 min synthesis time. A series of analytical tests was performed in order to prove the identity of the radiolabeled compound and its suitability for human applications.

Target site concentrations of ciprofloxacin after single intravenous and oral doses

To characterize the potential of ciprofloxacin penetration into human soft tissues following intravenous (i.v.) and oral (p.o.) administration, we measured the free ciprofloxacin concentrations in interstitial space fluid of skeletal muscle and subcutaneous adipose tissue by microdialysis. In addition, ciprofloxacin concentrations were measured in cantharis-induced skin blisters, saliva, and capillary plasma and were compared to the total concentrations in venous plasma. Furthermore, a pharmacodynamic in vitro model was used to simulate in vivo pharmacokinetics in bacterial culture. Eight healthy volunteers received ciprofloxacin in an open randomized crossover fashion either as a single i.v. infusion of 400 mg over 60 min or as a single p.o. dose of 500 mg. For both tissues the mean areas under the concentration-time curves (AUCs) for interstitial space fluid (AUC(interstitial fluid)s) were significantly lower than the corresponding AUC(plasma)s, with AUC(interstitial fluid)/AUC(plasma) ratios ranging from 0.38 to 0.68. For skeletal muscle, the AUC(interstitial fluid) was significantly higher after administration of 400 mg i.v. than after administration of 500 mg p.o., with a ratio of the AUC after p.o. administration/AUC after i.v. administration of 0.64. The ratio of the concentration in skeletal muscle/concentration in plasma increased over the entire observation period, implying that ciprofloxacin concentrations were not at steady state. The ratio of the concentration in skin blister fluid/concentration in plasma reached values above 4, indicating a preferential penetration of ciprofloxacin into inflamed lesions. The concentrations in saliva and capillary blood were similar to the corresponding total levels in plasma. In vitro both in vivo ciprofloxacin concentration-time profiles were equally effective against select bacterial strains. In conclusion, single-dose administration of two bioequivalent dosage forms of ciprofloxacin might lead to differences in target site pharmacokinetics. These differences, however, are not related to a difference in target site pharmacodynamics.