Dosing regimen matters: the importance of early intervention and rapid attainment of the pharmacokinetic/pharmacodynamic target

Potency of marbofloxacin for pig pneumonia pathogens Actinobacillus pleuropneumoniae and Pasteurella multocida: Comparison of growth media

Pharmacodynamic properties of marbofloxacin were established for six isolates each of the pig respiratory tract pathogens, Actinobacillus pleuropneumoniae and Pasteurella multocida. Three in vitro indices of potency were determined; Minimum Inhibitory Concentration (MIC), Minimum Bactericidal Concentration (MBC) and Mutant Prevention Concentration (MPC). For MIC determination Clinical Laboratory Standards Institute guidelines were modified in three respects: (1) comparison was made between two growth media, an artificial broth and pig serum; (2) a high inoculum count was used to simulate heavy clinical bacteriological loads; and (3) five overlapping sets of two-fold dilutions were used to improve accuracy of determinations. Similar methods were used for MBC and MPC estimations. MIC and MPC serum:broth ratios for A. pleuropneumoniae were 0.79:1 and 0.99:1, respectively, and corresponding values for P. multocida were 1.12:1 and 1.32:1. Serum protein binding of marbofloxacin was 49%, so that fraction unbound (fu) serum MIC values were significantly lower than those predicted by correction for protein binding; fu serum:broth MIC ratios were 0.40:1 (A. pleuropneumoniae) and 0.50:1 (P. multocida). For broth, MPC:MIC ratios were 13.7:1 (A. pleuropneumoniae) and 14.2:1 (P. multocida). Corresponding ratios for serum were similar, 17.2:1 and 18.8:1, respectively. It is suggested that, for dose prediction purposes, serum data might be preferable to potency indices measured in broths.

Survey of pharmacists’ antibiotic dosing recommendations for sustained low-efficiency dialysis

BACKGROUND

The use of hybrid renal replacement therapies like sustained low efficiency dialysis (SLED) is increasing in ICUs worldwide. However, pharmacokinetic studies designed to inform therapeutic antibiotic dosing in critically ill patients receiving SLED are limited. SLED operational characteristics vary across institutions. Pharmacists in institutions that utilize SLED are challenged to recommend therapeutic doses for antibiotics.

OBJECTIVE

To characterize pharmacist-recommended antibiotic regimens for SLED.

METHODS

An electronic survey was sent to pharmacist members of the American College of Clinical Pharmacy in the Nephrology or Critical Care Practice and Research Network. Dosing recommendations for a hypothetical critically ill septic patient were collected for cefepime, ceftaroline, daptomycin, levofloxacin, meropenem, and piperacillin/tazobactam. Main outcome measure Antibiotic regimens for the six antibiotics, their frequency, pharmacist’s experience with renal replacement therapies (RRT), post-graduate training, years of clinical experience, number of staffed beds in their hospital, and RRT employed in their ICUs.

RESULTS

The survey was completed by 69 clinical pharmacists who had 8.5 ± 7.5 (mean ± SD) years of experience. All pharmacists had experience dosing medications for patients receiving RRT. The most frequently recommended regimen for each antibiotic was: cefepime 1000 mg every 24 h, ceftaroline 200 mg every 12 h, daptomycin 6 mg/kg every 24 h, levofloxacin 500 mg every 24 h, meropenem 1000 mg every 12 h, and piperacillin/tazobactam 2250 mg every 8 h. Up to nine distinct regimens were recommended for each antibiotic, and the total daily dose between these regimens ranged by as much as a 12-fold. Neither pharmacist’s experience with SLED, post-graduate training, nor years of clinical experience were significantly associated with particular dosing recommendations for the antibiotics.

CONCLUSION

Pharmacists working in institutions that utilize SLED make antibiotic dosing recommendations that vary 4–12-fold depending on the drug. Published research does not provide adequate guidance to optimally dose antibiotics in patients receiving SLED. More SLED pharmacokinetic trials, real-time serum concentration monitoring and advanced pharmacokinetic modeling techniques are necessary to ensure therapeutic dosing in patients receiving SLED.

Bayesian Estimation of Tobramycin Exposure in Patients with Cystic Fibrosis

Fixed tobramycin (mg/kg) dosing is often inappropriate in patients with cystic fibrosis (CF), as pharmacokinetics are highly variable. The area under the concentration-time curve (AUC) is an exposure metric suited to monitoring in this population. Bayesian strategies to estimate AUC have been available for over 20 years but are not standard practice in the clinical setting. To assess their suitability for use in clinical practice, three AUC estimation methods using limited sampling were compared to measured true exposure by using intensive sampling tobramycin data. Adults prescribed once daily intravenous tobramycin had eight concentrations taken over 24 h. An estimate of true exposure within one dosing interval was calculated using the trapezoidal method and compared to three alternate estimates determined using (i) a two-sample log-linear regression (LLR) method (local hospital practice); (ii) a Bayesian estimate using one concentration (AUC₁); and (iii) a Bayesian estimate using two concentrations (AUC₂). Each method was evaluated against the true measured exposure by a Bland-Altman analysis. Twelve patients with a median (range) age and weight of 25 (18 to 36) years and 66.5 (51 to 76) kg, respectively, were recruited. There was good agreement between the true exposure and the three alternate estimates of AUC, with a mean AUC bias of <10 mg/liter · h in each case, i.e., -8.2 (LLR), 3.8 (AUC₁), and 1.0 (AUC₂). Bayesian analysis-based and LLR estimation methods of tobramycin AUC are equivalent to true exposure estimation. All three methods may be suitable for use in the clinical setting; however, a one-sample Bayesian method may be most useful in ambulatory patients for which coordinating blood samples is difficult. Suitably powered, randomized clinical trials are required to assess patient outcomes.

Characterization of In Vitro Resistance Development to the Novel Echinocandin CD101 in Candida Species

CD101 is a novel echinocandin with a long half-life undergoing clinical development for treatment of candidemia/invasive candidiasis and vulvovaginal candidiasis. The potential for and mechanisms underlying the development of resistance to CD101 in Candida species were investigated by using spontaneous resistance and serial passage selection methodologies. Four Candida spp. (C. albicans, C. glabrata, C. parapsilosis, and C. krusei) were chosen for resistance characterization with CD101, anidulafungin, and caspofungin. The frequency of spontaneous, single-step mutations conferring reduced susceptibility to CD101 at 1× the agar growth inhibition concentration was low across all species, with median frequencies ranging from 1.35 × 10(-8) to 3.86 × 10(-9), similar to ranges generated for anidulafungin and caspofungin. Serial passage of Candida spp. on agar plates containing drug gradients demonstrated a low potential for resistance development, with passage 20 CD101-selected strains possessing increases in MICs equivalent to or lower than those for the majority of strains generated under selection with anidulafungin and caspofungin. A total of 12 fks "hot spot" mutations were identified, typically in strains with the highest MIC shifts. Cross-resistance was broadly observed among the 3 echinocandins evaluated, with no CD101-selected mutants (with or without fks hot spot mutations) exhibiting reduced susceptibility to CD101 but not also to anidulafungin and/or caspofungin. Consistent with currently approved echinocandins, CD101 demonstrates a low potential for resistance development, which could be further enhanced in vivo by the high maximum concentration of drug in serum (Cmax)/area under the concentration-time curve (AUC) plasma drug exposure achieved with once-weekly dosing of CD101.

Colistin loading dose: evaluation of the published pharmacokinetic and clinical data

Colistin (polymyxin E) has been widely used since the beginning of the century as a last-option antibiotic for the treatment of patients with multidrug-resistant and extensively-drug resistant bacterial infections. However, colistin dosing is troublesome because each batch of the drug contains a mixture of components and because it is administered as the inactive pro-drug colistimethate sodium (CMS), which has different pharmacokinetic (PK) properties from the active drug. Significant inter-individual and intra-individual variability in colistin plasma concentrations have been observed in all available studies. Low plasma concentrations of the drug during the first hours from initiation of administration suggested that a loading dose would be appropriate. However, other PK studies challenge this approach. Clinical data from randomised controlled trials are not available, whilst data from observational studies do not support higher effectiveness of a loading dose. In this review, we summarise the available data regarding the administration of a loading dose and discuss the issues surrounding the potential advantages and disadvantages as well as the context within which such an approach could be beneficial to patients.

Tracking Cefoperazone/Sulbactam Resistance Development In vivo in A. baumannii Isolated from a Patient with Hospital-Acquired Pneumonia by Whole-Genome Sequencing

Cefoperazone/sulbactam has been shown to be efficacious for the treatment of infections caused by Acinetobacter baumannii; however, the mechanism underlying resistance to this synergistic combination is not well understood. In the present study, two A. baumannii isolates, AB1845 and AB2092, were isolated from a patient with hospital-acquired pneumonia before and after 20 days of cefoperazone/sulbactam therapy (2:1, 3 g every 8 h with a 1-h infusion). The minimum inhibitory concentration (MIC) of cefoperazone/sulbactam for AB1845 and AB2092 was 16/8 and 128/64 mg/L, respectively. Blood samples were collected on day 4 of the treatment to determine the concentration of cefoperazone and sulbactam. The pharmacokinetic/pharmacodynamic (PK/PD) indices (%T_>MIC) were calculated to evaluate the dosage regimen and resistance development. The results showed that %T_>MIC of cefoperazone and sulbactam was 100% and 34.5% for AB1845, and 0% and 0% for AB2092, respectively. Although there was no available PK/PD target for sulbactam, it was proposed that sulbactam should be administered at higher doses or for prolonged infusion times to achieve better efficacy. To investigate the mechanism of A. baumannii resistance to the cefoperazone/sulbactam combination in vivo, whole-genome sequencing of these two isolates was further performed. The sequencing results showed that 97.6% of the genome sequences were identical and 33 non-synonymous mutations were detected between AB1845 and AB2092. The only difference of these two isolates was showed in sequencing coverage comparison. There was a 6-kb amplified DNA fragment which was three times higher in AB2092, compared with AB1845. The amplified DNA fragment containing the bla_OXA-23 gene on transposon Tn2009. Further quantitative real-time PCR results demonstrated that gene expression at the mRNA level of bla_OXA-23 was >5 times higher in AB2092 than in AB1845. These results suggested that the bla_OXA-23 gene had higher expression level in AB2092 via gene amplification and following transcription. Because gene amplification plays a critical role in antibiotic resistance in many bacteria, it is very likely that the bla_OXA-23 amplification results in the development of cefoperazone/sulbactam resistance in vivo.

Impact of Timing and Dosage of a Fluoroquinolone Treatment on the Microbiological, Pathological, and Clinical Outcomes of Calves Challenged with Mannheimia haemolytica

The efficacy of an early and low inoculum-adjusted marbofloxacin treatment was evaluated on microbiological and clinical outcomes in calves infected with 4.10⁷ CFU of Mannheimia haemolytica A1. Twenty-two calves were included based on their rectal temperature rise in the 10 h after challenge and allocated in four groups, receiving a single intramuscular injection of saline (CON), 2 mg/kg marbofloxacin 2–4 h after inclusion (early treatment, E2), 2 or 10 mg/kg marbofloxacin 35–39 h after inclusion (late treatments, L2, L10). In CON calves, M. haemolytica DNA loads in bronchoalveolar lavages continuously increased from inclusion to day 4, and were associated with persistent respiratory clinical signs and lung lesions. At times of early and late treatments, M. haemolytica loads ranged within 3.5–4 and 5.5–6 log₁₀ DNA copies/mL, respectively. Early 2 mg/kg marbofloxacin treatment led to rapid and total elimination of bacteria in all calves. The late treatments induced a reduction of bacterial loads, but 3 of 6 L2 and 1 of 6 L10 calves were still positive for M. haemolytica at day 4. Except for CON calves, all animals exhibited clinical improvement within 24 h after treatment. However, early 2 mg/kg treatment was more efficacious to prevent pulmonary lesions, as indicated by the reduction of the extension and severity of gross lesions and by the histopathological scores. These results demonstrated for the first time that a reduced antibiotic regimen given at an early stage of the disease and targeting a low bacterial load could be efficacious in a natural bovine model of pneumonia.

Legionnaires' disease

Since first identified in early 1977, bacteria of the genus Legionella are recognised as a common cause of community-acquired pneumonia and a rare cause of hospital-acquired pneumonia. Legionella bacteria multisystem manifestations mainly affect susceptible patients as a result of age, underlying debilitating conditions, or immunosuppression. Water is the major natural reservoir for Legionella, and the pathogen is found in many different natural and artificial aquatic environments such as cooling towers or water systems in buildings, including hospitals. The term given to the severe pneumonia and systemic infection caused by Legionella bacteria is Legionnaires' disease. Over time, the prevalence of legionellosis or Legionnaires' disease has risen, which might indicate a greater awareness and reporting of the disease. Advances in microbiology have led to a better understanding of the ecological niches and pathogenesis of the condition. Legionnaires' disease is not always suspected because of its non-specific symptoms, and the diagnostic tests routinely available do not offer the desired sensitivity. However, effective antibiotics are available. Disease notification systems provide the basis for initiating investigations and limiting the scale and recurrence of outbreaks. This report reviews our current understanding of this disease.

A Randomized Clinical Trial of Single-Dose Versus Weekly Dalbavancin for Treatment of Acute Bacterial Skin and Skin Structure Infection

BACKGROUND

Acute bacterial skin and skin structure infections (ABSSSIs) are a cause of significant morbidity and therapy can be a burden to the healthcare system. New antibiotics that simplify treatment and avoid hospitalization are needed. This study compared the safety and efficacy of a single intravenous infusion of 1500 mg of dalbavancin to the 2-dose regimen.

METHODS

This study was a randomized, double-blind trial in patients aged >18 years with ABSSSIs. Patients were randomized to dalbavancin 1500 mg either as a single intravenous (IV) infusion or 1000 mg IV on day 1 followed 1 week later by 500 mg IV. The primary endpoint was a ≥20% reduction in the area of erythema at 48-72 hours in the intent-to-treat population. Noninferiority was to be declared if the lower limit of the 95% confidence interval (CI) on the difference in the outcomes was greater than -10%. Clinical outcome was also assessed at days 14 and 28.

RESULTS

Six hundred ninety-eight patients were randomized. Demographic characteristics were similar on each regimen, although there were more patients with methicillin-resistant Staphylococcus aureus (MRSA) at baseline on the 2-dose regimen (36/210 [17.1%] vs 61/220 [27.7%]). Dalbavancin delivered as a single dose was noninferior to a 2-dose regimen (81.4% vs 84.2%; difference, -2.9% [95% CI, -8.5% to 2.8%]). Clinical outcomes were also similar at day 14 (84.0% vs 84.8%), day 28 (84.5% vs 85.1%), and day 14 in clinically evaluable patients with MRSA in a baseline culture (92.9% vs 95.3%) in the single- and 2-dose regimens, respectively. Treatment-emergent adverse events occurred in 20.1% of the single-dose patients and 19.9% on the 2-dose regimen.

CONCLUSIONS

A single 1500-mg infusion of dalbavancin is noninferior to a 2-dose regimen, has a similar safety profile, and removes logistical constraints related to delivery of the second dose.

CLINICAL TRIALS REGISTRATION

NCT02127970.

Addressing Concerns about Changing the Route of Antimicrobial Administration from Intravenous to Oral in Adult Inpatients

BACKGROUND

Many health care institutions are in the process of establishing antimicrobial stewardship programs. Changing the route of administration of antimicrobial agents from intravenous to oral (IV to PO) is a simple, well-recognized intervention that is often part of an antimicrobial stewardship program. However, the attending health care team may have concerns about making this switch.

OBJECTIVES

To provide insights into common concerns related to IV to PO conversion, with the aim of helping antimicrobial stewardship teams to address them.

DATA SOURCES

Published clinical trials and reviews were identified from a literature search of Ovid MEDLINE with the keywords (step down or switch or conversion or transition or sequential) and (antibiotics or antibacterial agents or antimicrobial or anti-infective agents).

DATA SYNTHESIS

The following issues are addressed in this review: benefits of the oral route, serum concentrations yielded by the oral formulation, source of pharmacokinetic data, clinical outcomes, provision of care in the intensive care unit, fear of therapeutic failure, and administration of antimicrobials via feeding tube.

CONCLUSIONS

When considering a change to oral therapy, it is important to have a thorough understanding of key aspects of the antimicrobial agent, the patient, and the disease being treated. The antimicrobial stewardship team has an important role in facilitating IV to PO conversion, educating prescribers, and addressing any concerns or reservations that may interfere with timely transition from IV to PO administration.

Recent Updates on the Role of Pharmacokinetics-pharmacodynamics in Antimicrobial Susceptibility Testing as Applied to Clinical Practice

Given current challenges in antimicrobial resistance and drug development, infectious diseases clinicians must rely on their own ingenuity to effectively treat infections while preserving the current antimicrobial armamentarium. An understanding of pharmacokinetics (PK), pharmacodynamics (PD), antimicrobial susceptibility testing (AST), and how these concepts relate, is essential to this task. In this review, we discuss how and why PK-PD impacts AST and the way infectious diseases are being treated, with a particular focus on vancomycin for methicillin-resistant Staphylococcus aureus, penicillin for Streptococcus pneumoniae, and an update on cephalosporins for Enterobacteriaceae. Finally, we address how new ideas to exploit PK-PD can promote innovative study design and bring about more rapid regulatory review of new antimicrobials.

Integration of PK/PD for dose optimization of Cefquinome against Staphylococcus aureus causing septicemia in cattle

Cefquinome is a fourth generation cephalosporin with antimicrobial activity against gram negative and gram positive bacterial species, including Staphylococcus aureus. The aim of our study was to observe the ex-vivo activity of cefquinome against Staphylococcus aureus strains by using bovine serum from intravenously treated cattle. Cefquinome kinetics were measured by liquid chromatography and UV detection. In vitro post antibiotic effects (PAEs) and mutant prevention concentrations were determined with S. aureus strain ATCC 12598. Cefquinome exhibited time-dependent killing and produced in vitro PAEs increasing with concentration and time of exposure. A pharmacokinetic-pharmacodynamic model was established to simulate the efficacy of cefquinome for different dosage regimens. A dosage of 2 mg/kg every 12 h for 3 days was expected to reach a bactericidal activity against S. aureus in case of septicemia.

Vancomycin continuous infusion versus intermittent infusion during continuous venovenous hemofiltration: slow and steady may win the race

Background

Vancomycin during continuous venovenous hemofiltration (CVVH) is either administered by intermittent infusion (II) or continuous infusion (CI). In this patient population, the best method to rapidly achieve target serum concentrations of 15 mcg/ml to 25 mcg/ml remains to be elucidated. We hypothesized that CI would achieve a target serum level of 15 mcg/ml to 25 mcg/ml within 24 h of the initiation of therapy more consistently than II.

Methods

A retrospective cohort study of adult patients admitted to the intensive care unit (ICU) between 2011 and 2014 receiving intravenous vancomycin with 24-hour serum level while on CVVH was included. Patients were excluded from this review if they had residual renal function during CVVH, were concomitantly on extracorporeal membrane oxygenation, or if the first dose of vancomycin was received six or more hours prior to the initiation of CVVH. The primary outcome was the achievement of a therapeutic level of 15mcg/ml to 25 mcg/ml by 24 hours.

Results

Fifty-nine patients met the inclusion criteria and 14 received CI and 45 in II. Therapeutic 24-hour levels were achieved in 14/14 versus 2/45 in CI and II, respectively (p < 0.001). Mean 24-hour vancomycin levels were 20.35 ± 2.78 mcg/ml for CI compared to 9.7 ± 3.52 mcg/ml for II (p < 0.001). Mean loading dose was 26.65 ± 3.06 mg/kg for CI compared to 17.58 ± 5.72 mg/kg for II (p < 0.001). Daily maintenance doses were 15.66 ± 6.26 mg/kg for CI compared to 17.28 ± 4.96 mg/kg for II (p = 0.339). In the subgroup of 27 patients who received vancomycin-loading dose >20 mg/kg, mean 24-hour levels were 20.35 ± 2.78 mcg/ml for CI versus 11.8 ± 2.7 mcg/ml for II (p < 0.001). No significant differences were found between patients in the two groups with respect to CVVH rate and length of CVVH prior to vancomycin administration.

Conclusions

The results of our study suggest that critically ill patients on CVVH treated with CI achieved the target level faster than II and consistently keep the vancomycin level within target range.

Using a sequential regimen to eliminate bacteria at sublethal antibiotic dosages

We need to find ways of enhancing the potency of existing antibiotics, and, with this in mind, we begin with an unusual question: how low can antibiotic dosages be and yet bacterial clearance still be observed? Seeking to optimise the simultaneous use of two antibiotics, we use the minimal dose at which clearance is observed in an in vitro experimental model of antibiotic treatment as a criterion to distinguish the best and worst treatments of a bacterium, Escherichia coli. Our aim is to compare a combination treatment consisting of two synergistic antibiotics to so-called sequential treatments in which the choice of antibiotic to administer can change with each round of treatment. Using mathematical predictions validated by the E. coli treatment model, we show that clearance of the bacterium can be achieved using sequential treatments at antibiotic dosages so low that the equivalent two-drug combination treatments are ineffective. Seeking to treat the bacterium in testing circumstances, we purposefully study an E. coli strain that has a multidrug pump encoded in its chromosome that effluxes both antibiotics. Genomic amplifications that increase the number of pumps expressed per cell can cause the failure of high-dose combination treatments, yet, as we show, sequentially treated populations can still collapse. However, dual resistance due to the pump means that the antibiotics must be carefully deployed and not all sublethal sequential treatments succeed. A screen of 136 96-h-long sequential treatments determined five of these that could clear the bacterium at sublethal dosages in all replicate populations, even though none had done so by 24 h. These successes can be attributed to a collateral sensitivity whereby cross-resistance due to the duplicated pump proves insufficient to stop a reduction in E. coli growth rate following drug exchanges, a reduction that proves large enough for appropriately chosen drug switches to clear the bacterium.

A laboratory treatment model shows that the sequentially alternating use of two antibiotics can be optimized to outperform combination treatments at the equivalent dose.

So-called “cocktail” treatments are often proposed as a way of enhancing the potency of antibiotics, based on the idea that multiple drugs can synergise when used together as part of a single combined therapy. We investigated whether any other multidrug deployment strategies are as effective as—or perhaps even better than—synergistic antibiotic combinations at reducing bacterial densities. “Collateral sensitivities” between antibiotics are frequently observed; this is when measures taken by a bacterium to counter the presence of one antibiotic sensitise it to the subsequent use of another. Our approach was to see if we could exploit these sensitivities by first deploying one drug, then removing it and instead deploying another, and then repeating this process. This is not an entirely new idea, and there is a precedence for this form of treatment that has been trialled in the clinic for Helicobacter pylori infection. The idea we pursued here is an extension of “sequential treatment”; we investigated whether with two antibiotics and n rounds of treatment, if we search within the set of all possible 2ⁿ “sequential treatments”—including the two single-drug monotherapies—there might be treatments within that set that are more effective than the equivalent two-drug cocktail. Using a simple in vitro treatment model, we show that some sequential-in-time antibiotic treatments are successful under conditions that cause the failure of the cocktail treatment when implemented at the equivalent dosage.

ACVIM consensus statement on therapeutic antimicrobial use in animals and antimicrobial resistance

The epidemic of antimicrobial resistant infections continues to challenge, compromising animal care, complicating food animal production and posing zoonotic disease risks. While the overall role of therapeutic antimicrobial use in animals in the development AMR in animal and human pathogens is poorly defined, veterinarians must consider the impacts of antimicrobial use in animal and take steps to optimize antimicrobial use, so as to maximize the health benefits to animals while minimizing the likelihood of antimicrobial resistance and other adverse effects. This consensus statement aims to provide guidance on the therapeutic use of antimicrobials in animals, balancing the need for effective therapy with minimizing development of antimicrobial resistance in bacteria from animals and humans.

Antimicrobial considerations in the perioperative patient

Surgical site infections are among the complications that can be reduced with the timely implementation of appropriate antimicrobial therapy. A 3-D approach to judicious antimicrobial use focuses on the de-escalation of systemic antimicrobial therapy, design of dosing regimens, and decontamination of the surgeon, patient, and environment. De-escalation can be accomplished in part through proper antimicrobial prophylaxis. Dosing regimens should be designed to maximize efficacy and minimize resistance. Decontamination includes disinfection of inanimate surfaces and timely application of appropriate antiseptics at concentrations that maximize efficacy.

Role of therapeutic drug monitoring in pulmonary infections: use and potential for expanded use of dried blood spot samples

Respiratory tract infections are among the most common infections in men. We reviewed literature to document their pharmacological treatments, and the extent to which therapeutic drug monitoring (TDM) is needed during treatment. We subsequently examined potential use of dried blood spots as sample procedure for TDM. TDM was found to be an important component of clinical care for many (but not all) pulmonary infections. For gentamicin, linezolid, voriconazole and posaconazole dried blood spot methods and their use in TDM were already evident in literature. For glycopeptides, β-lactam antibiotics and fluoroquinolones it was determined that development of a dried blood spot (DBS) method could be useful. This review identifies specific antibiotics for which development of DBS methods could support the optimization of treatment of pulmonary infections.

Applications of the pharmacokinetic/pharmacodynamic (PK/PD) analysis of antimicrobial agents

The alarming increase of resistance against multiple currently available antibiotics is leading to a rapid lose of treatment options against infectious diseases. Since the antibiotic resistance is partially due to a misuse or abuse of the antibiotics, this situation can be reverted when improving their use. One strategy is the optimization of the antimicrobial dosing regimens. In fact, inappropriate drug choice and suboptimal dosing are two major factors that should be considered because they lead to the emergence of drug resistance and consequently, poorer clinical outcomes. Pharmacokinetic/pharmacodynamic (PK/PD) analysis in combination with Monte Carlo simulation allows to optimize dosing regimens of the antibiotic agents in order to conserve their therapeutic value. Therefore, the aim of this review is to explain the basis of the PK/PD analysis and associated techniques, and provide a brief revision of the applications of PK/PD analysis from a therapeutic point-of-view. The establishment and reevaluation of clinical breakpoints is the sticking point in antibiotic therapy as the clinical use of the antibiotics depends on them. Two methodologies are described to establish the PK/PD breakpoints, which are a big part of the clinical breakpoint setting machine. Furthermore, the main subpopulations of patients with altered characteristics that can condition the PK/PD behavior (such as critically ill, elderly, pediatric or obese patients) and therefore, the outcome of the antibiotic therapy, are reviewed. Finally, some recommendations are provided from a PK/PD point of view to enhance the efficacy of prophylaxis protocols used in surgery.

Antibiotic Dosing in Patients With Acute Kidney Injury: "Enough But Not Too Much"

Increasing evidence suggests that antibiotic dosing in critically ill patients with acute kidney injury (AKI) often does not achieve pharmacodynamic goals, and the continued high mortality rate due to infectious causes appears to confirm these findings. Although there are compelling reasons why clinicians should use more aggressive antibiotic dosing, particularly in patients receiving aggressive renal replacement therapies, concerns for toxicity associated with higher doses are real. The presence of multisystem organ failure and polypharmacy predispose these patients to drug toxicity. This article examines the pharmacokinetic and pharmacodynamic consequences of critical illness, AKI, and renal replacement therapy and describes potential solutions to help clinicians give "enough but not too much" in these very complicated patients.

Pharmacokinetics and pharmacodynamics of aerosolized antibacterial agents in chronically infected cystic fibrosis patients

Bacteria adapt to growth in lungs of patients with cystic fibrosis (CF) by selection of heterogeneously resistant variants that are not detected by conventional susceptibility testing but are selected for rapidly during antibacterial treatment. Therefore, total bacterial counts and antibiotic susceptibilities are misleading indicators of infection and are not helpful as guides for therapy decisions or efficacy endpoints. High drug concentrations delivered by aerosol may maximize efficacy, as decreased drug susceptibilities of the pathogens are compensated for by high target site concentrations. However, reductions of the bacterial load in sputum and improvements in lung function were within the same ranges following aerosolized and conventional therapies. Furthermore, the use of conventional pharmacokinetic/pharmacodynamic (PK/PD) surrogates correlating pharmacokinetics in serum with clinical cure and presumed or proven eradication of the pathogen as a basis for PK/PD investigations in CF patients is irrelevant, as minimization of systemic exposure is one of the main objectives of aerosolized therapy; in addition, bacterial pathogens cannot be eradicated, and chronic infection cannot be cured. Consequently, conventional PK/PD surrogates are not applicable to CF patients. It is nonetheless obvious that systemic exposure of patients, with all its sequelae, is minimized and that the burden of oral treatment for CF patients suffering from chronic infections is reduced.

Evaluation of meropenem regimens suppressing emergence of resistance in Acinetobacter baumannii with human simulated exposure in an in vitro intravenous-infusion hollow-fiber infection model

The emergence of resistance to carbapenems in Pseudomonas aeruginosa can be suppressed by optimizing the administration of meropenem. However, whether the same is true for Acinetobacter baumannii is not fully understood. We assessed the bactericidal activity of meropenem and its potency to suppress the emergence of resistance in A. baumannii with human simulated exposure in an in vitro intravenous-infusion hollow-fiber infection model (HFIM). Two clinical strains of carbapenem-susceptible multidrug-resistant A. baumannii (CS-MDRAB), CSRA24 and CSRA91, were used, and their MICs and mutant prevention concentrations (MPCs) were determined. Six meropenem dosage regimens (0.5, 1.0, or 2.0 g given every 8 h [q8h] with a 0.5-h or 3-h infusion for seven consecutive days) were simulated and then evaluated in the HFIM. Both the total population and resistant subpopulations of the two strains were quantified. Drug concentrations were measured by high-performance liquid chromatography. All dosage regimens, except for the lowest dosage (0.5 g for both the 0.5-h and 3-h infusions), showed 3-log CFU/ml bacterial killing. Dosage regimens of 2.0 g with 0.5-h and 3-h infusions exhibited an obvious bactericidal effect and suppressed resistance. Selective amplification of subpopulations with reduced susceptibility to meropenem was suppressed with a percentage of the dosage interval in which meropenem concentrations exceeded the MPC (T>MPC) of ≥20% or with a ratio of T>MPC to the percentage of the dosage interval in which drug concentrations are within the mutant selection window of ≥0.25. Our in vitro data support the use of a high dosage of meropenem (2.0 g q8h) for the treatment of severe infection caused by CS-MDRAB.

Testing the optimality properties of a dual antibiotic treatment in a two-locus, two-allele model

Mathematically speaking, it is self-evident that the optimal control of complex, dynamical systems with many interacting components cannot be achieved with 'non-responsive' control strategies that are constant through time. Although there are notable exceptions, this is usually how we design treatments with antimicrobial drugs when we give the same dose and the same antibiotic combination each day. Here, we use a frequency- and density-dependent pharmacogenetics mathematical model based on a standard, two-locus, two-allele representation of how bacteria resist antibiotics to probe the question of whether optimal antibiotic treatments might, in fact, be constant through time. The model describes the ecological and evolutionary dynamics of different sub-populations of the bacterium Escherichia coli that compete for a single limiting resource in a two-drug environment. We use in vitro evolutionary experiments to calibrate and test the model and show that antibiotic environments can support dynamically changing and heterogeneous population structures. We then demonstrate, theoretically and empirically, that the best treatment strategies should adapt through time and constant strategies are not optimal.

Simplified equations using two concentrations to calculate area under the curve for antimicrobials with concentration-dependent pharmacodynamics: daptomycin as a motivating example

The effects of several antimicrobial agents are predicted by the ratio of the area under the concentration-time curve (AUC) to the MIC (AUC/MIC). Peak (Cp) and trough (Ct) concentrations are often measured clinically as surrogates of AUC because actual computation of AUC from 1 or 2 samples requires sophisticated mathematical methods. Given that the effects of daptomycin are predicted by AUC/MIC, our objective was to compare simple equation calculated AUC based on Cp and Ct to model integrated AUC. A standard population pharmacokinetic model was used to simulate 5,000 daptomycin concentration-time profiles after 5 doses of 6 mg/kg of body weight/day (0.5-h infusions). The AUC for the 24-h period was computed by integration and by equations with 110 Cp-Ct combination pairs. The Cp time points were in 15-min increments between 0.5 h and 3 h and Ct in 15-min increments within an hour of the end of the dosing interval for each dose. The precision and bias of the calculated AUC relative to the integrated AUC were determined to identify Cp-Ct pairs associated with the lowest bias and highest precision. The equations were further validated using two daptomycin concentration-time data sets from healthy volunteers and critically ill patients. The precision and bias of calculated AUC were based primarily on Cp, and use of a daptomycin Cp 1.5 h to 3 h from the start of infusion was associated with a bias of <10% and an R(2) of >0.95. Data from the healthy volunteers and critically ill patients also demonstrated declining bias with use of Cp ≥ 1.5 h from the start of infusion with relatively good precision. Simplified equations using a daptomycin Cp approximately 2 h from the start of infusion and a Ct within an hour of the end of the dosing interval should yield precise and unbiased estimates of daptomycin AUC.

Comparative mutant prevention concentration and antibacterial activity of fluoroquinolones against Escherichia coli in diarrheic buffalo calves

Owing to emerging threat of antimicrobial resistance, mutant prevention concentration (MPC) is considered as an important parameter to evaluate the antimicrobials for their capacity to restrict/allow the emergence of resistant mutants. Therefore, MPCs of ciprofloxacin, enrofloxacin, levofloxacin, moxifloxacin, and norfloxacin were determined against Escherichia coli isolates of diarrheic buffalo calves. The minimum inhibitory concentrations (MICs) and minimum bactericidal concentrations (MBCs) were also established. The MICs of ciprofloxacin, enrofloxacin, levofloxacin, moxifloxacin and norfloxacin were 0·009, 0·022, 0·024, 0·028, and 0·036 μg/ml, respectively. The MBCs obtained were very close to the MICs of respective drugs that suggested a bactericidal mode of action of antimicrobials. The MPCs (μg/ml) of ciprofloxacin (4·2×MIC), moxifloxacin (4·8×MIC), and norfloxacin (5·1×MIC) were approximately equal but slightly lower than enrofloxacin (7·6×MIC) and levofloxacin (8·5×MIC) against clinical isolates of E. coli. The MPC data suggested that enrofloxacin has the potential for restricting the selection of E. coli mutants during treatment at appropriate dosing.

Experimental Simulation of the Effects of an Initial Antibiotic Treatment on a Subsequent Treatment after Initial Therapy Failure

Therapy failure of empirical antibiotic treatments prescribed by primary care physicians occurs commonly. The effect of such a treatment on the susceptibility to second line antimicrobial drugs is unknown. Resistance to amoxicillin was rapidly induced or selected in E. coli at concentrations expected in the patient's body. Strains with reduced susceptibility outcompeted the wild-type whenever antibiotics were present, even in low concentrations that did not affect the growth rates of both strains. Exposure of E. coli to amoxicillin caused moderate resistance to cefotaxime. The combined evidence suggests that initial treatment by amoxicillin has a negative effect on subsequent therapy with beta-lactam antibiotics.

Bugs, hosts and ICU environment: countering pan-resistance in nosocomial microbiota and treating bacterial infections in the critical care setting

ICUs are areas where resistance problems are the largest, and these constitute a major problem for the intensivist's clinical practice. Main resistance phenotypes among nosocomial microbiota are (i) vancomycin-resistance/heteroresistance and tolerance in grampositives (MRSA, enterococci) and (ii) efflux pumps/enzymatic resistance mechanisms (ESBLs, AmpC, metallo-betalactamases) in gramnegatives. These phenotypes are found at different rates in pathogens causing respiratory (nosocomial pneumonia/ventilator-associated pneumonia), bloodstream (primary bacteremia/catheter-associated bacteremia), urinary, intraabdominal and surgical wound infections and endocarditis in the ICU. New antibiotics are available to overcome non-susceptibility in grampositives; however, accumulation of resistance traits in gramnegatives has led to multidrug resistance, a worrisome problem nowadays. This article reviews microorganism/infection risk factors for multidrug resistance, suggesting adequate empirical treatments. Drugs, patient and environmental factors all play a role in the decision to prescribe/recommend antibiotic regimens in the specific ICU patient, implying that intensivists should be familiar with available drugs, environmental epidemiology and patient factors.

Low or high doses of cefquinome targeting low or high bacterial inocula cure Klebsiella pneumoniae lung infections but differentially impact the levels of antibiotic resistance in fecal flora

The combination of efficacious treatment against bacterial infections and mitigation of antibiotic resistance amplification in gut microbiota is a major challenge for antimicrobial therapy in food-producing animals. In rats, we evaluated the impact of cefquinome, a fourth-generation cephalosporin, on both Klebsiella pneumoniae lung infection and intestinal flora harboring CTX-M-producing Enterobacteriaceae. Germfree rats received a fecal flora specimen from specific-pathogen-free pigs, to which a CTX-M-producing Escherichia coli strain had been added. K. pneumoniae cells were inoculated in the lungs of these gnotobiotic rats by using either a low (10(5) CFU) or a high (10(9) CFU) inoculum. Without treatment, all animals infected with the low or high K. pneumoniae inoculum developed pneumonia and died before 120 h postchallenge. In the treated groups, the low-inoculum rats received a 4-day treatment of 5 mg/kg of body weight cefquinome beginning at 24 h postchallenge (prepatent phase of the disease), and the high-inoculum rats received a 4-day treatment of 50 mg/kg cefquinome beginning when the animals expressed clinical signs of infection (patent phase of the disease). The dose of 50 mg/kg targeting the high K. pneumoniae inoculum cured all the treated rats and resulted in a massive amplification of CTX-M-producing Enterobacteriaceae. A dose of 5 mg/kg targeting the low K. pneumoniae inoculum cured all the rats and averted an outbreak of clinical disease, all without any amplification of CTX-M-producing Enterobacteriaceae. These findings might have implications for the development of new antimicrobial treatment strategies that ensure a cure for bacterial infections while avoiding the amplification of resistance genes of human concern in the gut microbiota of food-producing animals.

Workshop report: the 2012 antimicrobial agents in veterinary medicine: exploring the consequences of antimicrobial drug use: a 3-D approach

Antimicrobial resistance is a global challenge that impacts both human and veterinary health care. The resilience of microbes is reflected in their ability to adapt and survive in spite of our best efforts to constrain their infectious capabilities. As science advances, many of the mechanisms for microbial survival and resistance element transfer have been identified. During the 2012 meeting of Antimicrobial Agents in Veterinary Medicine (AAVM), experts provided insights on such issues as use vs. resistance, the available tools for supporting appropriate drug use, the importance of meeting the therapeutic needs within the domestic animal health care, and the requirements associated with food safety and food security. This report aims to provide a summary of the presentations and discussions occurring during the 2012 AAVM with the goal of stimulating future discussions and enhancing the opportunity to establish creative and sustainable solutions that will guarantee the availability of an effective therapeutic arsenal for veterinary species.

Aggressive chemotherapy and the selection of drug resistant pathogens

Drug resistant pathogens are one of the key public health challenges of the 21^st century. There is a widespread belief that resistance is best managed by using drugs to rapidly eliminate target pathogens from patients so as to minimize the probability that pathogens acquire resistance de novo. Yet strong drug pressure imposes intense selection in favor of resistance through alleviation of competition with wild-type populations. Aggressive chemotherapy thus generates opposing evolutionary forces which together determine the rate of drug resistance emergence. Identifying treatment regimens which best retard resistance evolution while maximizing health gains and minimizing disease transmission requires empirical analysis of resistance evolution in vivo in conjunction with measures of clinical outcomes and infectiousness. Using rodent malaria in laboratory mice, we found that less aggressive chemotherapeutic regimens substantially reduced the probability of onward transmission of resistance (by >150-fold), without compromising health outcomes. Our experiments suggest that there may be cases where resistance evolution can be managed more effectively with treatment regimens other than those which reduce pathogen burdens as fast as possible.

Drug-resistance is a major public health problem. Conventional wisdom on resistance management is to use aggressive chemotherapy to kill pathogens as rapidly as possible so as to prevent them from acquiring resistance. This is the reason why physicians frequently exhort patients to finish drug courses even after they no longer feel sick. However, this approach is based on the notion that we need only prevent new resistant mutants from arising. We hypothesize that in the situation where such mutants are already present at the time of treatment, more aggressive chemotherapy will select for these the fastest by rapidly killing all sensitive competitors. Here we demonstrate in a rodent malaria model that such selection indeed occurs more intensely following aggressive treatment than following less aggressive treatment, without any benefit to host health or infectivity. This suggests that aggressive chemotherapy will not be the best way to retard resistance evolution in some - perhaps many - circumstances. We suggest that an evidence-based approach across a wide range of infectious diseases is needed to manage resistance evolution.

Pharmacodynamics of doxycycline and tetracycline against Staphylococcus pseudintermedius: proposal of canine-specific breakpoints for doxycycline

Doxycycline is a tetracycline that has been licensed for veterinary use in some countries, but no clinical breakpoints are available for veterinary pathogens. The objectives of this study were (i) to establish breakpoints for doxycycline and (ii) to evaluate the use of tetracycline as a surrogate to predict the doxycycline susceptibility of Staphylococcus pseudintermedius isolates. MICs and inhibition zone diameters were determined for 168 canine S. pseudintermedius isolates according to Clinical and Laboratory Standards Institute (CLSI) standards. Tetracycline resistance genes were detected by PCR, and time-kill curves were determined for representative strains. In vitro pharmacodynamic and target animal pharmacokinetic data were analyzed by Monte Carlo simulation (MCS) for the development of MIC interpretive criteria. Optimal zone diameter breakpoints were defined using the standard error rate-bounded method. The two drugs displayed bacteriostatic activity and bimodal MIC distributions. Doxycycline was more active than tetracycline in non-wild-type strains. MCS and target attainment analysis indicated a certainty of ≥ 90% for attaining an area under the curve (AUC)/MIC ratio of >25 with a standard dosage of doxycycline (5 mg/kg of body weight every 12 h) for strains with MICs of ≤ 0.125 μg/ml. Tetracycline predicted doxycycline susceptibility, but current tetracycline breakpoints were inappropriate for the interpretation of doxycycline susceptibility results. Accordingly, canine-specific doxycycline MIC breakpoints (susceptible, ≤ 0.125 μg/ml; intermediate, 0.25 μg/ml; resistant, ≥ 0.5 μg/ml) and zone diameter breakpoints (susceptible, ≥ 25 mm; intermediate, 21 to 24 mm; resistant, ≤ 20 mm) and surrogate tetracycline MIC breakpoints (susceptible, ≤ 0.25 μg/ml; intermediate, 0.5 μg/ml; resistant, ≥ 1 μg/ml) and zone diameter breakpoints (susceptible, ≥ 23 mm; intermediate, 18 to 22 mm; resistant, ≤ 17 mm) were proposed based on the data generated in this study.

Treatment of carbapenem-resistant Klebsiella pneumoniae: the state of the art

The increasing incidence of carbapenem-resistant Klebsiella pneumoniae (CR-KP) fundamentally alters the management of patients at risk to be colonized or infected by such microorganisms. Owing to the limitation in efficacy and potential for toxicity of the alternative agents, many experts recommend using combination therapy instead of monotherapy in CR-KP-infected patients. However, in the absence of well-designed comparative studies, the best combination for each infection type, the continued role for carbapenems in combination therapy and when combination therapy should be started remain open questions. Herein, the authors revise current microbiological and clinical evidences supporting combination therapy for CR-KP infections to address some of these issues.

Pharmacokinetics and pharmacodynamics of once-daily administration of intravenous tobramycin in adult patients with cystic fibrosis hospitalized for an acute pulmonary exacerbation

The serum pharmacokinetic profile of intravenous (i.v.) tobramycin administration was characterized for a sample of nine adult patients with cystic fibrosis (CF) who were hospitalized for an acute pulmonary exacerbation. Current recommended i.v. tobramycin dosing protocols are predicted through modeling and simulation to be suboptimal. Empirical tobramycin regimens of ≥15 mg/kg of body weight administered i.v. once daily should be evaluated for adult patients with CF to optimize outcomes.