What do we really know about antibiotic pharmacodynamics?

Endophytic bacteria of Gracilaria edulis in combating human bacterial pathogens by PPDHMP - A crude to single molecule product development approach

Resistance in human bacterial pathogens and lack of novel antibiotic development has led to the need for new antibiotics. Therefore, the current study was focused on endophytic bacteria from Gracilaria edulis, an edible seaweed, capable of synthesizing novel bioactive compounds with potential applications in the inhibition of human pathogens. The endophyte, identified as Bacillus subtilis through 16S rRNA gene sequencing, exhibited significant antibacterial activity against bacterial human pathogens. Using GC-MS, FTIR and NMR the lead compound was identified as Pyrrolo[1,2-α] pyrazine-1,4-dione, hexahydro-3-(2-methylpropyl) (PPDHMP). Optimized media composition using glucose, proline and valine significantly enhanced the production of PPDHMP which was observed by the increase in zone of inhibition. Molecular docking of PPDHMP indicated a high binding affinity to beta-lactamase, suggesting its potential as a beta-lactamase inhibitor. PPDHMP exhibited cell wall inhibitory activity and ADMET analysis revealed promising pharmacokinetic and toxicity profiles indicating its potential for further evaluation as an oral antibiotic candidate. Phytotoxicity assessments and hemolytic assay confirmed the non-toxic nature of the metabolites produced. This research highlights the immense potential of marine endophytes in addressing the escalating issue of antibiotic resistance and paves the way for innovative solutions in antimicrobial therapy.

Ceftiofur use and antimicrobial stewardship in the horse

Equine practitioners require recommendations that support antimicrobial stewardship and avoid generating resistance to medically important antibiotics. This review examines current inadequacies in antimicrobial stewardship standards within the veterinary community, related to antimicrobial categorisation and prescribing practices. Resistance to cephalosporin antibiotics in horses is also described. Properties of cephalosporin antibiotics are outlined and equine-specific studies of ceftiofur, a third-generation cephalosporin antibiotic with medical importance, are detailed. Readers are provided with recommendations that encourage appropriate use of ceftiofur, citing the evidence available in horses.

What Is the Best Vancomycin Therapeutic Drug Monitoring Parameter to Assess Efficacy? A Critical Review of Experimental Data and Assessment of the Need for Individual Patient Minimum Inhibitory Concentration Value

Therapeutic drug monitoring is recommended for the use of vancomycin, but a recent widely publicized US medical society consensus statement has changed the suggested optimal method(s) of dose adjustment. Specifically, 24 h area under the curve (AUC₂₄)-based monitoring is has been recommended for vancomycin in preference to monitoring of trough concentrations. One reason cited for this change is the claim that AUC₂₄ is a superior correlate to efficacy than trough (Cmin). Evidence from a number of retrospective analyses have been critically reviewed and determined to have weaknesses. This narrative review focuses on the experimental studies performed in vivo in animal models of infection and in vitro to determine the extent to which these data may provide a compelling distinction between pharmacokinetic/pharmacodynamics (PKPD) parameters that may translate to clinical use in therapeutic drug monitoring. Animal in vivo studies have been presented at conferences, but no original peer reviewed studies could be found that compare various PKPD parameters. These conference proceeding findings were supportive but unconvincing, even though they were favorably presented subsequently in review articles and clinical practice guidelines. In vitro data are somewhat conflicting, but the range of concentrations may play a role in the discrepancies found. It has been suggested that MIC may be assumed to have a value of 1 mg/L; however, it can be demonstrated that this assumption may lead to considerable discrepancy from results with an actual MIC value. The AUC₂₄ parameter has been weighed against the percentage of time above the MIC (%T > MIC) as a comparative PKPD parameter, yet this may be an inappropriate comparison for vancomycin since all clinically useful dosing provides 100% T > MIC. Regardless, there is a distinction between clinical TDM parameters and PKPD parameters, so, in practice, the change to AUC₂₄:MIC based on animal experiments and in vitro evidence for vancomycin may be premature.

Adjuvant antibiotic-loaded bone cement: Concerns with current use and research to make it work

Antibiotic-loaded bone cement (ALBC) is broadly used to treat orthopaedic infections based on the rationale that high-dose local delivery is essential to eradicate biofilm-associated bacteria. However, ALBC formulations are empirically based on drug susceptibility from routine laboratory testing, which is known to have limited clinical relevance for biofilms. There are also dosing concerns with nonstandardized, surgeon-directed, hand-mixed formulations, which have unknown release kinetics. On the basis of our knowledge of in vivo biofilms, pathogen virulence, safety issues with nonstandardized ALBC formulations, and questions about the cost-effectiveness of ALBC, there is a need to evaluate the evidence for this clinical practice. To this end, thought leaders in the field of musculoskeletal infection (MSKI) met on 1 August 2019 to review and debate published and anecdotal information, which highlighted four major concerns about current ALBC use: (a) substantial lack of level 1 evidence to demonstrate efficacy; (b) ALBC formulations become subtherapeutic following early release, which risks induction of antibiotic resistance, and exacerbated infection from microbial colonization of the carrier; (c) the absence of standardized formulation protocols, and Food and Drug Administration-approved high-dose ALBC products to use following resection in MSKI treatment; and (d) absence of a validated assay to determine the minimum biofilm eradication concentration to predict ALBC efficacy against patient specific micro-organisms. Here, we describe these concerns in detail, and propose areas in need of research.

Antibiotic-Loaded Hydrogel Coating to Reduce Early Postsurgical Infections in Aseptic Hip Revision Surgery: A Retrospective, Matched Case-Control Study

Periprosthetic joint infections (PJIs) are a cause of frequent implant failure in revision hip replacement surgery. The purpose of this study is to evaluate the onset of early postoperative infections in patients who underwent hip surgery with cementless prostheses treated with an antibiotic loaded hydrogel on their surface, in addition to systemic prophylaxis, and compare them to a control group. The secondary objective was to evaluate the onset of any local and systemic adverse effects and interference with bone ingrowth processes and functional recovery. A retrospective observational study was conducted on patients who underwent revision hip surgery by performing a 1:1 match between patients treated with an antibiotic hydrogel (ALH) and the control patients. The incidence of PJIs was assessed with a minimum of six months follow-up. Seventeen patients treated with the ALH were compared with 17 patients from the control group. No PJIs were reported in the ALH group versus the six cases encountered in the control group (p < 0.0001). No significant differences were reported with regard to prosthetic osseointegration and functional results, nor were there side effects in the ALH group. Despite the low sample size, the use of on-site prophylaxis with ALH has proven effective and safe in reducing the risk of PJIs in patients with a high risk for infections. Further studies are needed to validate these results in other implant-related surgeries.

Tarsocrural joint polymyxin B concentrations achieved following intravenous regional limb perfusion of the drug via a saphenous vein to healthy standing horses

OBJECTIVE

To determine whether therapeutic concentrations (> 0.5 to 1.0 μg/mL) of polymyxin B (PB) were achieved in the tarsocrural joint of horses when the drug was administered by IV regional limb perfusion (IV-RLP) via a saphenous vein at doses of 25, 50, and 300 mg and to describe any adverse systemic or local effects associated with such administration.

ANIMALS

9 healthy adult horses.

PROCEDURES

In the first of 2 experiments, 6 horses each received 25 and 50 mg of PB by IV-RLP via a saphenous vein with at least 2 weeks between treatments. For each treatment, a tourniquet was placed at the midmetatarsus and another was placed midway between the stifle joint and tarsus. Both tourniquets were removed 30 minutes after the assigned dose was administered. Blood and tarsocrural joint fluid samples were collected for determination of PB concentration before and at predetermined times after drug administration. In experiment 2, 4 horses were administered 300 mg of PB by IV-RLP in 1 randomly selected pelvic limb in a manner identical to that used in experiment 1.

RESULTS

For all 3 doses, the mean synovial fluid PB concentration was > 10 times the therapeutic concentration and below the level of quantification at 30 and 1,440 minutes after drug administration, respectively. No adverse systemic or local effects were observed following PB administration.

CONCLUSIONS AND CLINICAL RELEVANCE

Results suggested that IV-RLP of PB might be a viable alternative for treatment of horses with synovial infections caused by gram-negative bacteria.

Integrated pharmacokinetic-Pharmacodynamic (PK/PD) model to evaluate the in vivo antimicrobial activity of Marbofloxacin against Pasteurella multocida in piglets

Background

Marbofloxacin is a veterinary fluoroquinolone with high activity against Pasteurella multocida. We evaluated it’s in vivo activity against P. multocida based on in vivo time-kill data in swine using a tissue-cage model. A series of dosages ranging from 0.15 to 2.5 mg/kg were administered intramuscularly after challenge with P. multocida type B, serotype 2.

Results

The ratio of the 24 h area under the concentration-time curve divided by the minimum inhibitory concentration (AUC₂₄TCF/MIC) was the best PK/PD index correlated with the in vivo antibacterial effectiveness of marbofloxacin (R2 = 0.9279). The AUC₂₄TCF/MIC necessary to achieve a 1-log₁₀ CFU/ml reduction and a 3-log₁₀ CFU/ml (90% of the maximum response) reduction as calculated by an inhibitory sigmoid E_max model were 13.48 h and 57.70 h, respectively.

Conclusions

Marbofloxacin is adequate for the treatment of swine infected with P. multocida. The tissue-cage model played a significant role in achieving these PK/PD results.

Relative effectiveness of azithromycin in killing intracellular Porphyromonas gingivalis

Invasive infections by Porphyromonas gingivalis are associated with persistent periodontal attachment loss and can be difficult to eliminate by scaling and root planing. Azithromycin (AZM) inhibits P. gingivalis and is actively accumulated by most human cells. We used an in vitro infection model to compare the effectiveness of AZM in killing intracellular P. gingivalis to the combined regimen of amoxicillin (AMX) and metronidazole (MET). Transport of [3H]-AZM by human gingival fibroblasts was characterized. Monolayers of Smulow-Glickman gingival epithelial cells or gingival fibroblasts were infected with P. gingivalis (strain 33277 or W83). After extracellular bacteria were eliminated with teicoplanin, infected cells were treated with therapeutic concentrations of AZM, AMX, or AMX + MET. Viable intracellular bacteria were released by cell lysis and plated on blood agar for enumeration. Antimicrobial activity against planktonic P. gingivalis was also evaluated. While survival of intraepithelial P. gingivalis 33277 was not significantly different after treatment with the three regimens, survival in infected fibroblasts was significantly lower after AZM treatment (65.9 ± 5.5%) compared with AMX (92.2 ± 3.5%) or AMX + MET (79.8 ± 5.2%, P < 0.01). Carnitine, a competitive inhibitor of AZM transport, reduced killing by AZM by ~55% (P < 0.05). Survival of intrafibroblast P. gingivalis W83 was also significantly lower after AZM treatment compared with the other regimens (P < 0.05). At therapeutic concentrations, AZM was significantly more active against intracellular P. gingivalis than against planktonic P. gingivalis (P < 0.0083). Gingival epithelial cells and fibroblasts possess a transport system that accumulates AZM and enhances elimination of intracellular P. gingivalis. Compared with the combination of AMX and MET, AZM was equally effective against intraepithelial P. gingivalis 33277 and significantly more effective against both strains of P. gingivalis from infected gingival fibroblasts. The results suggest that AZM could be a reasonable alternative to the regimen of AMX and MET for periodontal patients who should not take these agents due to known side effects or compliance issues.

Application of PK/PD Modeling in Veterinary Field: Dose Optimization and Drug Resistance Prediction

Among veterinary drugs, antibiotics are frequently used. The true mean of antibiotic treatment is to administer dose of drug that will have enough high possibility of attaining the preferred curative effect, with adequately low chance of concentration associated toxicity. Rising of antibacterial resistance and lack of novel antibiotic is a global crisis; therefore there is an urgent need to overcome this problem. Inappropriate antibiotic selection, group treatment, and suboptimal dosing are mostly responsible for the mentioned problem. One approach to minimizing the antibacterial resistance is to optimize the dosage regimen. PK/PD model is important realm to be used for that purpose from several years. PK/PD model describes the relationship between drug potency, microorganism exposed to drug, and the effect observed. Proper use of the most modern PK/PD modeling approaches in veterinary medicine can optimize the dosage for patient, which in turn reduce toxicity and reduce the emergence of resistance. The aim of this review is to look at the existing state and application of PK/PD in veterinary medicine based on in vitro, in vivo, healthy, and disease model.

Treatment of community-acquired pneumonia

Community-acquired pneumonia is the sixth leading cause of death in the USA. Adherence to the 2007 Infectious Diseases Society of America/American Thoracic Society community-acquired pneumonia guidelines has been associated with improved clinical outcomes. However, choice between guideline-recommended treatments is at the discretion of the prescribing clinician. This review is intended to discuss the characteristics of these treatment options including dosing frequency, dose adjustment for renal/hepatic dysfunction, serious/common adverse events, drug interactions, lung penetration, pharmacokinetic-pharmacodynamic target and effect of obesity to help guide antimicrobial selection. An increasing portion of patients are receiving expanded empiric coverage for methicillin-resistant Staphylococcus aureus as recommended by the American Thoracic Society and Infectious Diseases Society of America for healthcare-associated pneumonia. However, this expanded coverage may not be achieving the desired improvements in clinical outcomes. We expect this increasingly diverse spectrum of patients with pneumonia to eventually result in the merger of these two guidelines to include all patients with pneumonia.

How to report and discuss ADME data in medicinal chemistry publications: in vitro data or in vivo extrapolations?

Early drug discovery projects often utilize data from ADME (absorption, distribution, metabolism, elimination) assays to benchmark data and guide discussion, rather than the predicted in vivo consequences of these data. Here, the two paradigms are compared, using evaluations of metabolic stability based on either microsomal clearance assay data or from the predicted in vivo hepatic clearance and half-life calculated through the combination of the venous well-stirred model and Øie-Tozer's model. The need for a shift in paradigm is presented, and its implications discussed. It is suggested that discussions about ADME data should revolve around potential clinical problems that are most likely to surface during the development phase, each benchmarked with a suitable variable derived from the assay data.

Pharmacokinetics and residue depletion of erythromycin in gilthead sea bream Sparus aurata L. after oral administration

Erythromycin (ERY) is an antibiotic effective against Streptococcus iniae, a microorganism responsible for significant losses in aquaculture. No data are available on the pharmacokinetics and residue depletion of ERY in sea bream. The aim of this study was thus to evaluate the pharmacokinetics of ERY in this species after a single oral administration at 75 mg kg(-1) b.w. and to assess its residue depletion from tissues after prolonged treatment for 10 days. ERY was rapidly absorbed in sea bream (Cmax  = 10.04 μg g(-1) and Tmax =1 h), with a half-life of 9.35 h and an AUC0-24 of 56.81 (h μg mL(-1) ). The data obtained and the evaluation of pharmacokinetic/pharmacodynamic parameters allowed us to hypothesize that dosage used in this study should be effective against S. iniae. A rapid reduction in erythromycin concentrations was observed in tissues, with the drug being detectable only during the first day post-treatment. In Europe, the use of ERY in aquaculture is allowed by off-label prescription with a withdrawal time of 500 °C day(-1) . The absence of ERY residues in tissues already at 24 h post-treatment suggests that ERY in sea bream should not pose human food safety issues.

Use of the respiratory fluoroquinolones for the outpatient management of community-acquired pneumonia

BACKGROUND

Approximately 4 million cases of community-acquired pneumonia (CAP) occur in the United States each year, with the majority treated on an outpatient basis. The first fluoroquinolones (eg, ciprofloxacin) were used with caution for respiratory tract infections due to limited in vitro activity against common gram-positive pathogens. With the availability of levofloxacin, followed by gatifloxacin and moxifloxacin hydrochloride, which exhibited increased activity against gram-positive organisms, the fluoroquinolones have become a practical choice for the treatment of CAP.

OBJECTIVE

The aim of this review was to compare the respiratory fluoroquinolones in the outpatient management of CAP.

METHODS

We conducted a search for English-language articles (key terms: fluoroquinolone, levofloxacin, gatifloxacin, moxifloxacin, and pneumonia; years: 1996-2004). Data from published literature were reviewed regarding clinical and microbiologic efficacy and tolerability; pharmacokinetic and pharmacodynamic properties; and drug costs of levofloxacin, gatifloxacin, and moxifloxacin.

RESULTS

The 3 fluoroquinolones reviewed showed comparable clinical and microbiologic efficacy for the treatment of CAP. In general, the fluoroquinolones were well tolerated, although some differences have been reported, including higher rates of gastrointestinal and other adverse events for gatifloxacin and moxifloxacin. Gatifloxacin and moxifloxacin exhibited greater in vitro potency than levofloxacin against Streptococcus pneumoniae. However, levofloxacin achieved a higher serum drug concentration than the other agents, allowing similar attainment of pharmacokinetic and pharmacodynamic targets required for effective treatment.

CONCLUSIONS

The respiratory fluoroquinolones provided appropriate first line treatment in select patients with CAP on the basis of their microbiologic and clinical efficacy and their safety profiles.

Anti-infective use in children and pregnancy: current deficiencies and future challenges

There are a number of challenges to using anti-infective agents in children and pregnant women. There is limited understanding of the altered pharmacokinetics of anti-infectives in these populations and as a result, optimized dosing regimens are yet to be established. The potential adverse effects of the drug on pregnancy outcome and the developing foetus is a major consideration, and the long term implications of drug side effects must be taken into account when drug exposure occurs early in life. These factors hinder research and licensing of new anti-infective drugs in these populations. We describe the current deficiencies and future challenges of anti-infective use in children and pregnant women, providing specific examples.

Antimicrobial agents, drug adverse reactions and interactions, and cancer

The intent of this chapter is to review the types of adverse drug reactions and interactions associated with antimicrobial agents, specifically in the setting of patients with malignancies. The initial sections will discuss categorizing and describing the mechanisms of adverse reactions and interactions. The later sections include a detailed discussion about adverse reactions and drug interactions associated with commonly used antibacterial, antiviral, and antifungal agents in this subpopulation. Where relevant, the clinical use and indication for the drugs will be reviewed. The antibacterial section will specifically address the emergence of antimicrobial resistance and drugs of last resort (newer agents, such as linezolid and daptomycin and novel uses of older previously retired agents, such as polymyxin B). The antifungal section will address the ramification of pharmacokinetic interactions and the need to measure drug levels. The chapter is not meant to be exhaustive and as such will not extensively address all antimicrobials or all interactions for each of these agents.

Pharmacokinetics and residue depletion of erythromycin in rainbow trout Oncorhynchus mykiss (Walbaum)

Erythromycin (ERY) is a drug active against Gram-positive bacteria such as Lactococcus garvieae, a pathogen responsible for an important disease that may cause a substantial decrease in rainbow trout Oncorhynchus mykiss (Walbaum) production, the species of fish most commonly produced in Italy. In the literature, studies on the kinetics behaviour of ERY in fish are limited. Therefore, the aim of the present study was to evaluate the pharmacokinetics of ERY in rainbow trout after a single oral treatment with 75 mg kg⁻¹ body weight (b.w.) of ERY and the residue depletion after multiple oral administration of 75 mg kg⁻¹ b.w. day⁻¹ of ERY for 10 days. Blood concentrations of ERY increased up to 20.24 ± 13.32 μg mL⁻¹ at 6 h, then decreased to 5.97 ± 3.89 μg mL⁻¹ at 24 h. The time during which the antibiotic remains in the bloodstream at concentrations exceeding the MIC (T > MIC) and the area under the serum concentration-time curve (AUC)/MIC are both pharmacokinetic-pharmacodynamic (PK/PD) predictors of ERY efficacy, and the data obtained allowed us to hypothesize that a dosage of 75 mg kg⁻¹ b.w. day⁻¹ of ERY could treat the lactococcosis in trout. Regarding the study of ERY depletion, rapid elimination was observed in tissue (muscle plus adherent skin); in fact the concentrations were below the limit of quantification in all samples (except two) by day 10 post-treatment. ERY is not licensed in Europe for use in aquaculture, and its use is possible only by off-label prescription with a precautionary withdrawal time of 500 degree-days, as established by Directive 2004/28/EC. From the data obtained in this study, a withdrawal time of 8.90 days was calculated, corresponding, in our experimental conditions, to 117.5 degree-days, a value significantly lower than that established by the European directive.

Pharmacokinetic study on pradofloxacin in the dog - comparison of serum analysis, ultrafiltration and tissue sampling after oral administration

BACKGROUND

Pradofloxacin, a newly developed 8-cyano-fluoroquinolone, show enhanced activity against Gram-positive organisms and anaerobes to treat canine and feline bacterial infections. The purpose of this cross-over study was to measure the unbound drug concentration of pradofloxacin in the interstitial fluid (ISF) using ultrafiltration and to compare the kinetics of pradofloxacin in serum, ISF and tissue using enrofloxacin as reference.

RESULTS

After oral administration of enrofloxacin (5 mg/kg) and pradofloxacin (3 mg/kg and 6 mg/kg, respectively), serum collection and ultrafiltration in regular intervals over a period of 24 h were performed, followed by tissue sampling at the end of the third dosing protocol (pradofloxacin 6 mg/kg). Peak concentrations of pradofloxacin (3 mg/kg) were 1.55±0.31 μg/ml in the ISF and 1.85±0.23 μg/ml in serum and for pradofloxacin (6 mg/kg) 2.71±0.81 μg/kg in the ISF and 2.77±0.64 μg/kg in serum; both without a statistical difference between ISF and serum. Comparison between all sampling approaches showed no consistent pattern of statistical differences.

CONCLUSIONS

Despite some technical shortcomings the ultrafiltration approach appears to be the most sensitive sampling technique to estimate pharmacokinetic values of pradofloxacin at the infection site. Pharmacokinetics - Pradofloxacin - Ultrafiltration - Dog - Oral Administration.

Pharmacokinetic and pharmacodynamic integration and modelling of marbofloxacin in calves for Mannheimia haemolytica and Pasteurella multocida

The pharmacokinetics (PK) and pharmacodynamics (PD) of marbofloxacin were established in calves for six strains of each of the pneumonia pathogens Mannheimia haemolytica and Pasteurella multocida. The distribution of marbofloxacin into inflamed (exudate) and non-inflamed (transudate) tissue cage fluids allowed comparison with the serum concentration-time profile. To establish the PD profile, minimum inhibitory concentration (MIC) was determined in Mueller-Hinton broth (MHB) and calf serum. Moderately higher MICs were obtained for serum compared to MHB. An initial integration of PK-PD data established C(max)/MIC ratios of 45.0 and AUC(24h)/MIC values of 174.7 h, based on serum MICs, for both bacterial species. Using bacterial time-kill curves, generated ex vivo for serum marbofloxacin concentrations, PK-PD modelling established three levels of growth inhibition: AUC(24 h)/MIC ratios for no reduction, 3 log(10) and 4 log(10) reductions in bacterial count from the initial inoculum count were 41.9, 59.5 and 68.0 h for M. haemolytica and 48.6, 64.9 and 74.8 h for P. multocida, on average respectively. Inter-strain variability for 3 log(10) and 4 log(10) reductions in bacterial count was smaller for P. multocida than for M. haemolytica. In conjunction with literature data on MIC(90) values, the present results allowed prediction of dosages for efficacy for each organism for the three levels of growth inhibition.

How to optimize the evaluation and use of antibiotics in neonates

The optimal evaluation and use of antibacterial agents that are very frequently prescribed in neonates during various situations such as early- and late-onset invasive infections depend on adapted dose selection, based on population pharmacokinetic/pharmacodynamic modeling and simulation, using approved surrogate biomarkers as pharmacodynamic end points. Data on efficacy can be extrapolated from adult and pediatric data because of comparable mechanistic action of antibiotics in neonates, children, and adults. However, evaluation of efficacy and toxicity in the neonate should always be discussed with regulatory agencies and are highly recommended when feasible.

Modeling the efficacy of trastuzumab-DM1, an antibody drug conjugate, in mice

Trastuzumab-DM1 (T-DM1) is a novel antibody-drug conjugate under investigation for the treatment of human epidermal growth factor receptor 2 (HER2)-positive metastatic breast cancer. One challenge in oncologic drug development is determining the optimal dose and treatment schedule. A novel dose regimen-finding strategy was developed for T-DM1 using experimental data and pharmacokinetic/pharmacodynamic modeling. To characterize the disposition of T-DM1, pharmacokinetic studies were conducted in athymic nude and beige nude mice. The pharmacokinetics of T-DM1 were described well by a two-compartment model. Tumor response data were obtained from single-dose, multiple-dose and time-dose-fractionation studies of T-DM1 in animal models of HER2-positive breast cancer, specifically engineered to be insensitive to trastuzumab. A sequential population-based pharmacokinetic/pharmacodynamic modeling approach was developed to describe the anti-tumor activity of T-DM1. A cell-cycle-phase nonspecific tumor cell kill model incorporating transit compartments captured well the features of tumor growth and the activity of T-DM1. Key findings of the model were that tumor cell growth rate played a significant role in the sensitivity of tumors to T-DM1; anti-tumor activity was schedule independent; and tumor response was linked to the ratio of exposure to a concentration required for tumor stasis.

Prospective monitoring of cefepime in intensive care unit adult patients

Introduction

Cefepime has been associated with a greater risk of mortality than other beta-lactams in patients treated for severe sepsis. Hypotheses for this failure include possible hidden side-effects (for example, neurological) or inappropriate pharmacokinetic/pharmacodynamic (PK/PD) parameters for bacteria with cefepime minimal inhibitory concentrations (MIC) at the highest limits of susceptibility (8 mg/l) or intermediate-resistance (16 mg/l) for pathogens such as Enterobacteriaceae, Pseudomonas aeruginosa and Staphylococcus aureus. We examined these issues in a prospective non-interventional study of 21 consecutive intensive care unit (ICU) adult patients treated with cefepime for nosocomial pneumonia.

Methods

Patients (median age 55.1 years, range 21.8 to 81.2) received intravenous cefepime at 2 g every 12 hours for creatinine clearance (CL_Cr) ≥ 50 ml/min, and 2 g every 24 hours or 36 hours for CL_Cr < 50 ml/minute. Cefepime plasma concentrations were determined at several time-points before and after drug administration by high-pressure liquid chromatography. PK/PD parameters were computed by standard non-compartmental analysis.

Results

Seventeen first-doses and 11 steady states (that is, four to six days after the first dose) were measured. Plasma levels varied greatly between individuals, from two- to three-fold at peak-concentrations to up to 40-fold at trough-concentrations. Nineteen out of 21 (90%) patients had PK/PD parameters comparable to literature values. Twenty-one of 21 (100%) patients had appropriate duration of cefepime concentrations above the MIC (T_>MIC ≥ 50%) for the pathogens recovered in this study (MIC ≤ 4 mg/l), but only 45 to 65% of them had appropriate coverage for potential pathogens with cefepime MIC ≥ 8 mg/l. Moreover, 2/21 (10%) patients with renal impairment (CL_Cr < 30 ml/minute) demonstrated accumulation of cefepime in the plasma (trough concentrations of 20 to 30 mg/l) in spite of dosage adjustment. Both had symptoms compatible with non-convulsive epilepsy (confusion and muscle jerks) that were not attributed to cefepime-toxicity until plasma levels were disclosed to the caretakers and symptoms resolved promptly after drug arrest.

Conclusions

These empirical results confirm the suspected risks of hidden side-effects and inappropriate PK/PD parameters (for pathogens with upper-limit MICs) in a population of ICU adult patients. Moreover, it identifies a safety and efficacy window for cefepime doses of 2 g every 12 hours in patients with a CL_Cr ≥ 50 ml/minute infected by pathogens with cefepime MICs ≤ 4 mg/l. On the other hand, prompt monitoring of cefepime plasma levels should be considered in case of lower CL_Cr or greater MICs.

Wild-type MIC distributions of four fluoroquinolones active against Mycobacterium tuberculosis in relation to current critical concentrations and available pharmacokinetic and pharmacodynamic data

OBJECTIVES

To describe wild-type distributions of the MIC of fluoroquinolones for Mycobacterium tuberculosis in relation to current critical concentrations used for drug susceptibility testing and pharmacokinetic/pharmacodynamic (PK/PD) data.

METHODS

A 96-stick replicator on Middlebrook 7H10 medium was used to define the MICs of ciprofloxacin, ofloxacin, moxifloxacin and levofloxacin for 90 consecutive clinical strains and 24 drug-resistant strains. The MICs were compared with routine BACTEC 460 susceptibility results and with MIC determinations in the BACTEC MGIT 960 system in a subset of strains using ofloxacin as a class representative. PK/PD data for each drug were reviewed in relation to the wild-type MIC distribution.

RESULTS

The wild-type MICs of ciprofloxacin, ofloxacin, moxifloxacin and levofloxacin were distributed from 0.125 to 1, 0.25 to 1, 0.032 to 0.5 and 0.125 to 0.5 mg/L, respectively. The MIC data correlated well with the BACTEC 960 MGIT and BACTEC 460 results. PD indices were the most favourable for levofloxacin, followed by moxifloxacin, ofloxacin and ciprofloxacin.

CONCLUSIONS

We propose S (susceptible) <or= 1.0 mg/L as the tentative epidemiological cut-off (ECOFF) for ofloxacin and ciprofloxacin, and S <or= 0.5 mg/L for levofloxacin and moxifloxacin, although it is possible that adding more MIC data could shift the ECOFFs for ofloxacin and levofloxacin one dilution upwards. The proposed ECOFFs may be more appropriate if used as clinical breakpoints on Middlebrook 7H10 agar than the current critical concentrations of S <or= 2.0 mg/L for ciprofloxacin, ofloxacin and levofloxacin, and S <or= 0.5 mg/L could be considered as a clinical breakpoint for moxifloxacin, provided other investigators can confirm our findings.

Basic PK/PD principles of drug effects in circular/proliferative systems for disease modelling

Disease progression modelling can provide information about the time course and outcome of pharmacological intervention on the disease. The basic PK/PD principles of proliferative and circular systems within the context of modelling disease progression and the effect of treatment thereupon are illustrated with the goal to better understand/predict eventual clinical outcome. Circular/proliferative systems can be very complex. To facilitate the understanding of how a dosing regimen can be defined in such systems we have shown the derivation of a system parameter named the Reproduction Minimum Inhibitory Concentration (RMIC) which represents the critical concentration at which the system switches from growth to extinction. The RMIC depends on two parameters (RMIC = (R₀ − 1) × IC₅₀): the basic reproductive ratio (R₀) a fundamental parameter of the circular/proliferative system that represents the number of offspring produced by one replicating species during its lifespan, and the IC₅₀, the potency of the drug to inhibit the proliferation of the system. The RMIC is constant for a given system and a given drug and represents the lowest concentration that needs to be achieved for eradication of the system. When exposure is higher than the RMIC, success can be expected in the long term. Time varying inhibition of replicating species proliferation is a natural consequence of the time varying inhibitor drug concentrations and when combined with the dynamics of the circular/proliferative system makes it difficult to predict the eventual outcome. Time varying inhibition of proliferative/circular systems can be handled by calculating the equivalent effective constant concentration (ECC), the constant plasma concentration that would give rise to the average inhibition at steady state. When ECC is higher than the RMIC, eradication of the system can be expected. In addition, it is shown that scenarios that have the same steady state ECC whatever the dose, dosage schedule or PK parameters have also the same average R₀ in the presence of the inhibitor (i.e. R_0-INH) and therefore lead to the same outcome. This allows predicting equivalent active doses and dosing schedules in circular and proliferative systems when the IC₅₀ and pharmacokinetic characteristics of the drugs are known. The results from the simulations performed demonstrate that, for a given system (defined by its RMIC), treatment success depends mainly on the pharmacokinetic characteristics of the drug and the dosing schedule.

Hospital visits and costs following outpatient treatment of CAP with levofloxacin or moxifloxacin

BACKGROUND

Hospital admissions (inpatient and emergency room) are a major source of medical costs for community-acquired pneumonia (CAP) initially treated in the outpatient setting. Current CAP treatment guidelines do not differentiate between outpatient treatment with levofloxacin and moxifloxacin.

OBJECTIVE

Compare health care resource use and medical costs to payers for CAP outpatients initiating treatment with levofloxacin or moxifloxacin.

RESEARCH DESIGN AND METHODS

CAP episodes were identified in the PharMetrics database between 2Q04 and 2Q07 based on: pneumonia diagnosis, chest X-ray and treatment with levofloxacin or moxifloxacin. Subsequent 30-day risk of pneumonia-related hospital visits and 30-day health care costs to payers for levofloxacin vs. moxifloxacin treatment were estimated after adjusting for pre-treatment demographics, health care resource use and pneumonia-specific risk factors using propensity score and exact factor matching.

RESULTS

A total of 15,472 levofloxacin- and 6474 moxifloxacin-initiated CAP patients were identified. Among 6352 matched pairs, levofloxacin treatment was associated with a 35% reduction in the odds of pneumonia-related hospital visits (odds ratio = 0.65, P = 0.004), lower per-patient costs for pneumonia-related hospital visits (102 dollars vs. 210 dollars, P = 0.001), lower pneumonia-related total costs (medical services and prescription drugs, 363 dollars vs. 491 dollars, P < 0.001) and lower total costs (1308 dollars vs. 1446 dollars, P < 0.001) vs. moxifloxacin over the 30-day observation period.

LIMITATIONS

Although observational analyses of claims data provide large sample sizes and reflect routine care, they do have several inherent limitations. Since randomization of subjects is not possible, adequate statistical techniques must be used to ensure that patient characteristics are well-balanced between treatment groups. In addition, data may be missing or miscoded.

CONCLUSIONS

CAP outpatients initiated with levofloxacin generated substantially lower costs to payers compared to matched patients initiated with moxifloxacin. The cost savings for patients initiated with levofloxacin were largely attributable to reduced rates of pneumonia-related hospitalization or ER visits.

Antimicrobial drug resistance

This chapter provides an overview of our current understanding of the mechanisms associated with the development of antimicrobial drug resistance, international differences in definitions of resistance, ongoing efforts to track shifts in drug susceptibility, and factors that can influence the selection of therapeutic intervention. The latter presents a matrix of complex variables that includes the mechanism of drug action, the pharmacokinetics (PK) of the antimicrobial agent in the targeted patient population, the pharmacodynamics (PD) of the bacterial response to the antimicrobial agent, the PK/PD relationship that will influence dose selection, and the integrity of the host immune system. Finally, the differences between bacterial tolerance and bacterial resistance are considered, and the potential for non-traditional anti-infective therapies is discussed.

Antimicrobial breakpoint estimation accounting for variability in pharmacokinetics

Background

Pharmacokinetic and pharmacodynamic (PK/PD) indices are increasingly being used in the microbiological field to assess the efficacy of a dosing regimen. In contrast to methods using MIC, PK/PD-based methods reflect in vivo conditions and are more predictive of efficacy. Unfortunately, they entail the use of one PK-derived value such as AUC or Cmax and may thus lead to biased efficiency information when the variability is large. The aim of the present work was to evaluate the efficacy of a treatment by adjusting classical breakpoint estimation methods to the situation of variable PK profiles.

Methods and results

We propose a logical generalisation of the usual AUC methods by introducing the concept of "efficiency" for a PK profile, which involves the efficacy function as a weight. We formulated these methods for both classes of concentration- and time-dependent antibiotics. Using drug models and in silico approaches, we provide a theoretical basis for characterizing the efficiency of a PK profile under in vivo conditions. We also used the particular case of variable drug intake to assess the effect of the variable PK profiles generated and to analyse the implications for breakpoint estimation.

Conclusion

Compared to traditional methods, our weighted AUC approach gives a more powerful PK/PD link and reveals, through examples, interesting issues about the uniqueness of therapeutic outcome indices and antibiotic resistance problems.

Functional relationship between bacterial cell density and the efficacy of antibiotics

OBJECTIVES

To determine the functional relationship between the density of bacteria and the pharmacodynamics of antibiotics, and the potential consequences of this inoculum effect on the microbiological course of antibiotic treatment of Staphylococcus aureus infections.

METHODS

In vitro time-kill, MIC estimation and antibiotic bioassay experiments were performed with S. aureus ATCC 25923 to ascertain the functional relationship between rates of kill and the MICs of six classes of antibiotics and the density of bacteria exposed. The potential consequences of the observed inoculum effects on the microbiological course of antibiotic treatment are explored with a mathematical model.

RESULTS

Modest or substantial inoculum effects on efficacy were observed for all six antibiotics studied, such as density-dependent declines in the rate and extent of antibiotic-mediated killing and increases in MIC. Although these measures of antibiotic efficacy declined with inoculum, this density effect did not increase monotonically. At higher densities, the rate of kill of ciprofloxacin and oxacillin declined with the antibiotic concentration. For daptomycin and vancomycin, much of this inoculum effect is due to density-dependent reductions in the effective concentration of the antibiotic. For the other four antibiotics, this density effect is primarily associated with a decrease in per-cell antibiotic concentration. With parameters in the range estimated, our mathematical model predicts that the course of antibiotic treatment can be affected by cell density; treatment protocols based on conventional (density-independent) MICs can fail to clear higher density infections.

CONCLUSIONS

The MICs used for pharmacokinetic/pharmacodynamic indices should be functions of the anticipated densities of the infecting population.

Pharmacokinetics of ceftazidime after intravenous and intramuscular administration to domestic cats

The pharmacokinetic properties of ceftazidime, a third generation cephalosporin, were investigated in five cats after single intravenous (IV) and intramuscular (IM) administration at a dose rate of 30 mg/kg. Minimum inhibitory concentrations (MICs) of ceftazidime for some Gram-negative (Escherichia coli, n=11) and Gram-positive (Staphylococcus spp., n=10) strains isolated from clinical cases were determined. An efficacy predictor, measured as the time over which the active drug exceeds the bacteria minimum inhibitory concentration (T>MIC), was calculated. Serum ceftazidime disposition was best fitted by a bi-compartmental and a mono-compartmental open model with first-order elimination after IV and IM dosing, respectively. After IV administration, distribution was rapid (t(1/2(d)) 0.04+/-0.03 h), with an area under the ceftazidime serum concentration:time curve (AUC((0-infinity))) of 173.14+/-48.69 microg h/mL and a volume of distribution (V((d(ss)))) of 0.18+/-0.04 L/kg. Furthermore, elimination was rapid with a plasma clearance of 0.19+/-0.08 L/hkg and a t(1/2) of 0.77+/-0.06 h. Peak serum concentration (C(max)), T(max), AUC((0-infinity)) and bioavailability for the IM administration were 89.42+/-12.15 microg/mL, 0.48+/-0.49 h, 192.68+/-65.28 microg h/mL and 82.47+/-14.37%, respectively. Ceftazidime MIC for E. coli ranged from 0.0625 to 32 microg/mL and for Staphylococcus spp. from 1 to 64 microg/mL. T>MIC was in the range 35-52% (IV) and 48-72% (IM) of the recommended dosing interval (8-12h) for bacteria with a MIC(90)4 microg/mL.

Pharmacokinetics of ceftriaxone after intravenous, intramuscular and subcutaneous administration to domestic cats

The pharmacokinetic properties of ceftriaxone, a third-generation cephalosporin, were investigated in five cats after single intravenous, intramuscular and subcutaneous administration at a dosage of 25 mg/kg. Ceftriaxone MICs for some gram-negative and positive strains isolated from clinical cases were determined. Efficacy predictor (t > MIC) was calculated. Serum ceftriaxone disposition was best fitted by a bicompartmental and a monocompartmental open models with first-order elimination after intravenous and intramuscular and subcutaneous dosing, respectively. After intravenous administration, distribution was fast (t1/2d 0.14 +/- 0.02 h) and moderate as reflected by the volume of distribution (V(d(ss))) of 0.57 +/- 0.22 L/kg. Furthermore, elimination was rapid with a plasma clearance of 0.37 +/- 0.13 L/h.kg and a t1/2 of 1.73 +/- 0.23 h. Peak serum concentration (Cmax), tmax and bioavailability for the intramuscular administration were 54.40 +/- 12.92 microg/mL, 0.33 +/- 0.07 h and 85.72 +/- 14.74%, respectively; and for the subcutaneous route the same parameters were 42.35 +/- 17.62 microg/mL, 1.27 +/- 0.95 h and 118.28 +/- 39.17%. Ceftriaxone MIC for gram-negative bacteria ranged from 0.0039 to >8 microg/mL and for gram-positive bacteria from 0.5 to 4 microg/mL. t > MIC was in the range 83.31-91.66% (10-12 h) of the recommended dosing interval (12 h) for Escherichia coli (MIC90 = 0.2 microg/mL).

Comparative Pharmacokinetics of Gentamicin after Intravenous, Intramuscular, Subcutaneous and Oral Administration in Broiler Chickens

The pharmacokinetics and bioavailability of gentamicin sulphate (5 mg/kg body weight) were studied in 50 female broiler chickens after single intravenous (i.v.), intramuscular (i.m.), subcutaneous (s.c.) and oral administration. Blood samples were collected at time 0 (pretreatment), and at 5, 15 and 30 min and 1, 2, 4, 6, 8, 12, 24 and 48 h after drug administration. Gentamicin concentrations were determined using a microbiological assay and Bacillus subtillis ATCC 6633 as a test organism. The limit of quantification was 0.2 microg/ml. The plasma concentration-time curves were analysed using non-compartmental methods based on statistical moment theory. Following i.v. administration, the elimination half-life (t (1/2beta)), the mean residence time (MRT), the volume of distribution at steady state (V (ss)), the volume of distribution (V (d,area)) and the total body clearance (Cl(B)) were 2.93 +/- 0.15 h, 2.08 +/- 0.12 h, 0.77 +/- 0.05 L/kg, 1.68 +/- 0.39 L/kg and 5.06 +/- 0.21 ml/min per kg, respectively. After i.m. and s.c. dosing, the mean peak plasma concentrations (C (max)) were 11.37 +/- 0.73 and 16.65 +/- 1.36 microg/ml, achieved at a post-injection times (t (max)) of 0.55 +/- 0.05 and 0.75 +/- 0.08 h, respectively. The t (1/2beta) was 2.87 +/- 0.44 and 3.48 +/- 0.37 h, respectively after i.m. and s.c. administration. The V (d,area) and Cl(B) were 1.49 +/- 0.21 L/kg and 6.18 +/- 0.31 ml/min per kg, respectively, after i.m. administration and were 1.43 +/- 0.19 L/kg and 4.7 +/- 0.33 ml/min per kg, respectively, after s.c. administration. The absolute bioavailability (F) of gentamicin after i.m. administration was lower (79%) than that after s.c. administration (100%). Substantial differences in the resultant kinetics data were obtained between i.m. and s.c. administration. The in vitro protein binding of gentamicin in chicken plasma was 6.46%.

Levofloxacin 750-mg for 5 days for the treatment of hospitalized Fine Risk Class III/IV community-acquired pneumonia patients

BACKGROUND

The efficacy and safety of 750-mg, 5-day levofloxacin was recently shown to be comparable to 500-mg, 10-day levofloxacin in a randomized, double-blind, multicentre clinical trial for mild-to-severe community-acquired pneumonia (CAP). This subgroup analysis attempted to compare the safety and efficacy of a short-course levofloxacin regimen with traditional levofloxacin dosing for PSI Class III/IV patients.

METHODS

This retrospective, subgroup analysis focused on Pneumonia Severity Index Class III and IV patients enrolled in the study. Measurements included clinical and microbiological success rates, adverse events, and symptom resolution by day 3 of therapy.

RESULTS

Of the 528 patients in the ITT population, 219 (41.5%) were categorized as PSI Class III/IV and included in this analysis. Among the clinically evaluable patients, 90.8% (69/76) of patients treated with the 750-mg regimen achieved clinical success, compared with 85.5% (71/83) treated with 500-mg levofloxacin (95% CI,-15.9 to 5.4). Eradication rates in the microbiologically evaluable population were comparable for the 750- and 500-mg regimens (88.9% vs 87.5%, respectively; 95% CI,-18.3 to 15.6). Both regimens were well tolerated and had comparable safety profiles. A greater proportion of patients in the 750-mg treatment group experienced resolution of fever (48.4% vs 34.0%; P=.046) and purulent sputum (48.4% vs 27.5%; P=.007) by day 3 of therapy.

CONCLUSIONS

The 750-mg, 5-day levofloxacin course achieved comparable clinical and microbiologic efficacy to the 500-mg, 10-day regimen. By day 3 of therapy, a greater proportion of patients in the 750-mg group had objective and subjective resolution of fever. Further research is needed to determine the economic significance of short-course levofloxacin therapy.

Prospective determination of plasma imipenem concentrations in critically ill children

Plasma imipenem concentrations were measured in 19 critically ill children (median age, 0.8 year; range, 0.02 to 12.9 years). Wide interindividual variations (2 to 4x at peak and >10x at trough concentrations) resulted in unpredictable plasma levels in several children. To avoid subtherapeutic drug levels, we recommend treatment with at least 100 mg/kg of body weight/day of imipenem-cilastatin for critically ill children requiring such therapy.

Integration of pharmacokinetic and pharmacodynamic indices of marbofloxacin in turkeys

Fluoroquinolones are extensively used in the treatment of systemic bacterial infections in poultry, including systemic Escherichia coli bacillosis, which is a common disease in turkey flocks. Marbofloxacin has been licensed for use in various mammalian species, but not as yet for turkeys, although its kinetic properties distinguish it from other fluoroquinolones. For example, the longer half-life of marbofloxacin in many animal species has been appreciated in veterinary practice. It is generally accepted that, for fluoroquinolones, the optimal dose should be estimated on the basis of the pharmacokinetic (PK) and pharmacodynamic (PD) characteristics of the drug under consideration. Knowledge of these specific data for the target animal species allows the establishment of an integrated PK-PD model that is of high predictive value. In the present study, the antibacterial efficacy (PD indices) against a field isolate of Escherichia coli O78/K80 was investigated ex vivo following oral and intravenous administration of marbofloxacin to turkeys (breed BUT 9; six animals per group) at a dose of 2 mg/kg of body weight (BW). At the same time, the serum concentrations of marbofloxacin were measured at different time intervals by a standardized high-performance liquid chromatography method, allowing the calculation of the most relevant kinetic parameters (PK parameters). The in vitro serum inhibitory activity of marbofloxacin against the selected E. coli strain, O78/K80, was 0.5 mug/ml in the blood serum of turkeys, and the ratio of the maximum concentration of the drug in serum to the serum inhibitory activity was 1.34. The lowest ratio of the measured serum concentration multiplied by the incubation period of 24 h to the serum inhibitory activity required for bacterial elimination was lower than the ratio of the area under the serum concentration-time curve (AUC) to the serum inhibitory activity. These first results suggested that the recommended dose of 2 mg/kg BW of marbofloxacin is sufficient to achieve a therapeutic effect in diseased animals. However, considering the risk of resistance induction, the applied dose should be equal to an AUC/MIC of >125, the generally recommended dose for all fluoroquinolones. According to the PK-PD results presented here, a dose of 3.0 to 12.0 mg/kg BW per day would be needed to meet this criterion. In conclusion, the results of the present study provide the rationale for an optimal dose regimen for marbofloxacin in turkeys and hence should form the basis for dose selection in forthcoming clinical trials.

Drug-induced acute kidney injury

PURPOSE OF REVIEW

The purpose of this review is to describe the most prevalent mechanisms of drug-induced acute kidney injury, to define the risk factors for nephrotoxicity, and to analyze the available evidence for preventive measures.

RECENT FINDINGS

Drug toxicity remains an important cause of acute kidney injury that, in many circumstances, can be prevented or at least minimized by vigilance and early intervention. Recent studies have resulted in increased insight into the subcellular mechanisms of drug nephrotoxicity. Further improvement is to be expected from the identification of early markers of nephrotoxicity and an increasing involvement of a clinical pharmacist.

SUMMARY

The main mechanisms of nephrotoxicity are vasoconstriction, altered intraglomerular hemodynamics, tubular cell toxicity, interstitial nephritis, crystal deposition, thrombotic microangiopathy, and osmotic nephrosis. Before prescribing a potentially nephrotoxic drug, the risk-to-benefit ratio and the availability of alternative drugs should be considered. Modifiable risk factors should be corrected. The correct drug dosage should be prescribed. Patients should be pre-hydrated and the glomerular filtration rate should be frequently monitored during the administration of a potentially nephrotoxic drug. Studies are needed to further elucidate the mechanisms of nephrotoxicity to design more-rational prevention and treatment strategies. Computer-based prescriber-order entry and an appropriately trained intensive care unit pharmacist are particularly helpful to minimize medication errors and adverse drug events.

Antibacterial dosing in intensive care: pharmacokinetics, degree of disease and pharmacodynamics of sepsis

Treatment of sepsis remains a significant challenge with persisting high mortality and morbidity. Early and appropriate antibacterial therapy remains an important intervention for such patients. To optimise antibacterial therapy, the clinician must possess knowledge of the pharmacokinetic and pharmacodynamic properties of commonly used antibacterials and how these parameters may be affected by the constellation of pathophysiological changes occurring during sepsis. Sepsis, and the treatment thereof, increases renal preload and, via capillary permeability, leads to 'third-spacing', both resulting in higher antibacterial clearances. Alternatively, sepsis can induce multiple organ dysfunction, including renal and/or hepatic dysfunction, causing a decrease in antibacterial clearance. Aminoglycosides are concentration-dependent antibacterials and they display an increased volume of distribution (V(d)) in sepsis, resulting in decreased peak serum concentrations. Reduced clearance from renal dysfunction would increase the likelihood of toxicity. Individualised dosing using extended interval dosing, which maximises the peak serum drug concentration (C(max))/minimum inhibitory concentration ratio is recommended. Beta-lactams and carbapenems are time-dependent antibacterials. An increase in V(d) and renal clearance will require increased dosing or administration by continuous infusion. If renal impairment occurs a corresponding dose reduction may be required. Vancomycin displays predominantly time-dependent pharmacodynamic properties and probably requires higher than conventionally recommended doses because of an increased V(d) and clearance during sepsis without organ dysfunction. However, optimal dosing regimens remain unresolved. The poor penetration of vancomycin into solid organs may require alternative therapies when sepsis involves solid organs (e.g. lung). Ciprofloxacin displays largely concentration-dependent kill characteristics, but also exerts some time-dependent effects. The V(d) of ciprofloxacin is not altered with fluid shifts or over time, and thus no alterations of standard doses are required unless renal dysfunction occurs. In order to optimise antibacterial regimens in patients with sepsis, the pathophysiological effects of systemic inflammatory response syndrome need consideration, in conjunction with knowledge of the different kill characteristics of the various antibacterial classes. In conclusion, certain antibacterials can have a very high V(d), therefore leading to a low C(max) and if a high peak is needed, then this would lead to underdosing. The V(d) of certain antibacterials, namely aminoglycosides and vancomycin, changes over time, which means dosing may need to be altered over time. Some patients with serum creatinine values within the normal range can have very high drug clearances, thereby producing low serum drug levels and again leading to underdosing.

Synthesis and antibacterial activity of 3-substituted-6-(3-ethyl-4-methylanilino)uracils

Numerous 3-substituted-6-(3-ethyl-4-methylanilino)uracils (EMAU) have been synthesized and screened for their capacity to inhibit the replication-specific bacterial DNA polymerase IIIC (pol IIIC) and the growth of Gram+ bacteria in culture. Direct alkylation of 2-methoxy-6-amino-4-pyrimidone produced the N3-substituted derivatives, which were separated from the byproduct 4-alkoxy analogues. The N3-substituted derivatives were heated with a mixture of 3-ethyl-4-methylaniline and its hydrochloride to effect displacement of the 6-amino group and simultaneous demethylation of the 2-methoxy group to yield target compounds in good yields. Certain intermediates, e.g. the 3-(iodoalkyl) compounds, were converted to a variety of (3-substituted-alkyl)-EMAUs by displacement. Most compounds were potent competitive inhibitors of pol IIIC (K(i)s 0.02-0.5 microM), and those with neutral, moderately polar 3-substituents had potent antibacterial activity against Gram+ organisms in culture (MICs 0.125-10 microg/mL). Several compounds protected mice from lethal intraperitoneal (ip) infections with S. aureus (Smith) when given by the ip route. A water soluble derivative, 3-(4-morpholinylbutyl)-EMAU hydrochloride, given subcutaneously, prolonged the life of infected mice in a dose dependent manner.

Overview of the Potency of Moxifloxacin Ophthalmic Solution 0.5% (VIGAMOX®)

Antibiotics have been the mainstay of therapy for infectious diseases since their origins in the 1940s. As microorganisms changed and resistance developed, more advanced antibiotics were ultimately needed to provide adequate coverage and spectrum. By selecting optimal antibiotics and dosing regimens, clinicians can avoid treatment failures and adverse events and can help prevent the emergence of further antibiotic resistance. The fourth-generation ophthalmic fluoroquinolones include moxifloxacin (VIGAMOX, Alcon Laboratories, Inc., Fort Worth, TX) and gatifloxacin (Zymar, Allergan, Irvine, CA), and they are now approved for the treatment of bacterial conjunctivitis. This review highlights four scientific methods that compare and rank antibiotic potencies and predict their clinical efficacy and their propensity to develop resistance: 1) in vitro assay for minimum inhibitory concentrations, 2) in vivo models for pharmacokinetic and pharamacodynamic properties, 3) therapeutic index or inhibitory quotient, and 4) in vitro assay for mutant prevention concentration. The fourth-generation ophthalmic fluoroquinolones perform well in these assays. Both antibiotics have better in vitro activity against gram-positive bacteria than ciprofloxacin or ofloxacin. Moxifloxacin penetrates better into ocular tissues than gatifloxacin and older fluoroquinolones; in vitro activity of moxifloxacin and gatifloxacin against gram-negative bacteria is similar to that of older fluoroquinolones. Moxifloxacin also has better mutant prevention characteristics than other fluoroquinolones. These findings support the use of the newer fluoroquinolones for the prevention and treatment of serious ophthalmic infections (e.g., keratitis, endophthalmitis) caused by susceptible bacteria.