MIC Discrepancies between Parenteral and Oral Anti-Staphylococcal Beta-Lactams among MSSA

INTRODUCTION

Recent evidence has shown that oral antibiotic therapy is not inferior to IV antibiotic therapy in the treatment of complicated Staphylococcus aureus infections. Therefore, oral antibiotic therapy is now frequently prescribed in clinical practice due to cost benefit, ease of administration, decreased complication rate, and lack of need for IV access. In vitro susceptibility testing for β-lactam oral antibiotics is not routinely performed as the guidelines provided by the Clinical and Laboratory Standards Institute (CLSI) recommend using oxacillin and cefoxitin as surrogate markers. Hence, oral antibiotic susceptibilities for cephalexin and dicloxacillin are not reported and implied based on oxacillin and cefoxitin. The objective of the current study was to determine whether susceptibilities among S. aureus isolates are predictable when comparing commonly used IV and oral beta-lactams.

METHODS

Cefazolin, cephalexin, dicloxacillin, and oxacillin broth microdilution minimum inhibitory concentrations (MICs) were determined for 100 clinical isolates of methicillin-sensitive S. aureus by broth microdilution following CLSI guidelines.

RESULTS

Among these isolates, median MICs for cephalexin were eight-fold higher than cefazolin MICs and median MICs for dicloxacillin were four-fold less than oxacillin MICs. Ten percent of more strains studied had a major or very major error in its susceptibility reporting when cephalexin was compared to its surrogate marker oxacillin.

DISCUSSIONS/CONCLUSIONS

The variations in MICs observed compounded with the dosing and pharmacokinetic differences of oral versus IV β-lactam suggests that establishing breakpoints for oral β-lactam antibiotics is necessary to ensure adequate therapy is selected for the treatment of complex S. aureus infections.

Examining the combination of cefixime and amoxicillin/clavulanate against extended-spectrum beta-lactamase (ESBL)-producing Escherichia coli isolates

INTRODUCTION

Community-acquired urinary tract infections (UTIs) caused by extended spectrum beta-lactamase (ESBL)-producing Escherichia coli have limited oral therapeutic options and pose significant clinical challenges. The goal of this study was to evaluate the in vitro synergy between CFM and AMC against ESBL E. coli with aims to identify an oral treatment option for UTIs.

METHODS

Minimum inhibitory concentrations (MICs) of CFM in the presence of AMC were determined for 46 clinical isolates by placing a CFM Etest on a plate with AMC impregnated in the agar. Isolates with CFM MIC ≤1 µg/ml in the presence of AMC were considered susceptible to the CFM and AMC combination. Five isolates were then selected for further testing using time-kill analysis in the presence of CFM, AMC, and CFM with AMC. Time-kill curves were plotted to determine synergy over 24 hours.

RESULTS

AMC improved the activity of CFM against ESBL E. coli isolates by 128-fold in the Etest analysis with 85% of tested isolates being susceptible to the combination. Four-fold or greater reduction in CFM MIC was exhibited in 44 of 46 (96%) isolates when in the presence of AMC. Synergy and bactericidal activity between CFM and AMC were exhibited in each of the five isolates tested by time-kill analysis.

DISCUSSION/CONCLUSION

This study found that AMC improves the activity of CFM against ESBL E. coli and that this antibiotic combination has potential as an oral therapeutic option to treat ESBL E. coli UTIs.

Exploring the Role of Piperacillin and Tazobactam in Combination with Vancomycin against Methicillin-Resistant Staphylococcus aureus

Previous studies have demonstrated synergy between piperacillin (PIP)-tazobactam (TAZ) (TZP) and vancomycin (VAN) against methicillin-resistant Staphylococcus aureus (MRSA). However, it is unknown whether PIP and/or TAZ synergizes with VAN against MRSA. We sought to determine whether PIP and/or TAZ synergizes with VAN against MRSA in vitro. The activity of PIP and/or TAZ with and without VAN (1/2 the minimum inhibitory concentration) was tested against 5 clinical MRSA isolates using a 24-h time-kill methodology. Antibiotic susceptibilities, accessory gene regulator (agr) operon functionality, and US strain type were also determined for the isolates. The combination of VAN and TZP was bactericidal against 3/5 isolates and synergistic against 4/5 isolates tested. Neither PIP nor TAZ alone combined with VAN demonstrated a significant reduction in bacterial growth. The combination of TZP and VAN was less active against the lone isolate with agr dysfunction. In summation, the combination of VAN with both PIP and TAZ was required for synergy against MRSA. This antibiotic combination may not be effective against unique MRSA strain types.

Clinical and Economic Effects of a Pharmacist-Administered Antiretroviral Therapy Adherence Clinic for Patients Living with HIV

BACKGROUND

Pharmacists have demonstrated the ability to improve patient adherence to antiretroviral therapy (ART).

OBJECTIVE

To determine the clinical and economic effects of a pharmacist-administered ART adherence clinic for patients living with human immunodeficiency virus (HIV).

METHODS

This pilot study with a pretest-posttest design examined the effect of a pharmacy adherence clinic on patient HIV viral load and CD4 count over a 6-month period. Patients with documented adherence problems were referred to the clinic. The pharmacist counseled patients at baseline and met with patients 1-2 weeks, 6 weeks, 3 months, and 6 months after starting ART. A societal perspective net cost analysis of the pharmacy adherence clinic was conducted to assess the economic efficiency of the intervention.

RESULTS

Twenty-eight patients were enrolled in the study, and 16 patients reached completion. Median HIV RNA significantly decreased from 48,000 copies/mL (interquartile range [IQR] = 16,750-139,000) to undetectable (< 20 copies/mL) at 6 months for all study participants who completed the full intervention (P = 0.001). In the 3 months following the intervention, we estimated that it prevented approximately 0.13 secondary HIV infections among the sexual partners of the 16 participants who completed the intervention. The total cost of the intervention was $16,811 ($1,051 per patient), which was less than the future savings in averted HIV-related medical care expenditures ($49,702).

CONCLUSIONS

A pharmacy adherence clinic that focused on early and sustained ART adherence interventions helped patients with documented medication adherence problems achieve an undetectable HIV RNA. The intervention was highly cost saving, with a return of nearly $3 in future medical care savings per dollar spent on the intervention.

DISCLOSURES

This work was supported in part by a research grant to Dilworth, Mercier, and Borrego from the American Society of Health-System Pharmacists Foundation. Klein and Pinkerton were supported in part by grants T32-MH19985 and P30-MH52776, respectively, from the National Institute of Mental Health. No funding bodies had any role in the study design, data collection, analysis, decision to publish, or preparation of the manuscript. The findings and conclusions in this article are those of the authors and do not necessarily represent the official position of the Health Resources and Services Administration. The authors have no conflicts of interest to disclose. Study concept and design were contributed primarily by Dilworth, Mercier, and Borrego, along with the other authors. Dilworth took the lead in data collection, along with Pinkerton, Klein, Mercier, and Jakeman. Data interpretation was performed by Dilworth and Pinkerton, along with the other authors. The manuscript was written by Dilworth, Klein, and Jakeman, with assistance from the other authors, and revised by Dilworth, Jakeman, and Klein, with assistance from the other authors. The results from this study were presented in part at the 2015 United States Conference on AIDS in Washington, DC, on September 10-13, 2015.

Clinical Impact of a Rapid Streptococcal Antigen Test on Antibiotic Use in Adult Patients

INTRODUCTION

Adult pharyngitis is rarely attributable to group A streptococci. Utilization of a rapid streptococcal antigen test (RADT) may improve appropriate prescribing for bacterial pharyngitis.

METHODS

Clinic 1 performed RADTs with subsequent Group A DNA probe test (GADNA) from November 2014-March 2015 and November 2015-March 2016 while Clinic 2 was the control clinic, then implemented the RADT with a GADNA from November 2015-March 2016. All GADNA results were obtained for each clinic from October 2013-March 2016.

RESULTS

At Clinic 1, 22.2% versus 8.5% of patients received inappropriately prescribed antibiotics for a GADNA or RADT result, respectively (p=0.048). For Clinic 2, 51.1% compared to 21.4% of patients were inappropriately prescribed antibiotic for a GADNA or RADT result, respectively (p=0.038). Overall, the total GADNA without RADT testing or RADTs with subsequent GADNA testing, 41.6% versus 11% of patients were inappropriately prescribed antibiotics, respectively (p=<0.0001).

CONCLUSION

Utilizing the RADT prevented unnecessary prescribing of antibiotics in adults.

An open-label, pragmatic, randomized controlled clinical trial to evaluate the comparative effectiveness of daptomycin versus vancomycin for the treatment of complicated skin and skin structure infection

Background

Treatment of complicated skin and skin structure infection (cSSSI) places a tremendous burden on the health care system. Understanding relative resource utilization associated with different antimicrobials is important for decision making by patients, health care providers, and payers.

Methods

The authors conducted an open-label, pragmatic, randomized (1:1) clinical study (N = 250) to compare the effectiveness of daptomycin with that of vancomycin for treatment of patients hospitalized with cSSSI caused by suspected or documented methicillin-resistant Staphylococcus aureus infection. The primary study end point was infection-related length of stay (IRLOS). Secondary end points included health care resource utilization, cost, clinical response, and patient-reported outcomes. Patient assessments were performed daily until the end of antibiotic therapy or until hospital discharge, and at 14 days and 30 days after discharge.

Results

No difference was found for IRLOS, total LOS, and total inpatient cost between cohorts. Hospital LOS contributed 85.9 % to the total hospitalization cost, compared with 6.4 % for drug costs. Daptomycin showed a nonsignificant trend toward a higher clinical success rate, compared with vancomycin, at treatment days 2 and 3. In the multivariate analyses, vancomycin was associated with a lower likelihood of day 2 clinical success (odds ratio [OR] = 0.498, 95 % confidence interval [CI], 0.249–0.997; P < 0.05).

Conclusion

This study did not provide conclusive evidence of the superiority of one treatment over the other in terms of clinical, economic, or patient outcomes. The data suggest that physician and patient preference, rather than drug acquisition cost, should be the primary driver of initial antibiotic selection for hospitalized patients with cSSSI.

Trial registration

ClinicalTrials.gov: NCT01419184 (Date: August 16, 2011)

Electronic supplementary material

The online version of this article (doi:10.1186/s12879-015-1261-9) contains supplementary material, which is available to authorized users.

Antimicrobial Stewardship Intervention and Feedback to Infectious Disease Specialists: A Case Study in High-Dose Daptomycin

Infectious Diseases specialists have used high-dose daptomycin (≥6 mg/kg/day) in select patients with difficult to treat methicillin-resistant Staphylococcus aureus (MRSA) or vancomycin-resistant Enterococcus (VRE) infections to optimize outcomes. Antimicrobial stewardship programs enforce antimicrobial formulary restrictions; however, interventions specifically aimed at Infectious Disease specialists can be particularly challenging. The purpose of this study was to create a high-dose daptomycin algorithm for Infectious Disease specialists that are consistent with best-practices. Daptomycin prescribing habits pre- and post-daptomycin algorithm implementation were evaluated using a quasi-experimental study design. Patients were included if ≥18 years of age and received daptomycin for ≥48 h. Patients were excluded if daptomycin was initiated on an outpatient setting. During the 12-month pre-intervention phase, 112 patients were included, with 73 patients in the 12-month post-intervention phase. A statistically significant decrease in the mean daptomycin dose from 9.01 mg/kg to 7.51 mg/kg (p < 0.005) was observed, resulting in an annual drug cost-savings of over $75,000 without adversely affecting readmission rates due to infection. Creation of a daptomycin algorithm with consideration of pathogen, disease state, and prior treatment, is an effective means of influencing prescribing habits of Infectious Disease specialists.

Impact of an intravenous trimethoprim/sulfamethoxazole shortage on treatment outcomes among HIV-infected patients with Pneumocystis jirovecii pneumonia

BACKGROUND

Trimethoprim/sulfamethoxazole (TMP/SMX) is the recommended first-line treatment for human immunodeficiency virus (HIV)-infected patients with Pneumocystis jirovecii pneumonia (PJP).However, in June 2010, the lone manufacturer of intravenous (IV) TMP/SMX in the United States stopped production of this medication. 

OBJECTIVES

To (a) evaluate the impact of the national IV TMP/SMX shortage on PJP treatment outcomes between 2 groups of HIV-infected patients-those treated before the shortage and those after the shortage-and (b) compare the length of hospital stay (LOS) and PJP treatment used before and after the shortage.

METHODS

A retrospective, quasi-experimental study examining 2 groups of HIV-infected adult patients with PJP was performed at an academic medical center from September 1, 2008, to June 30, 2012. Patients treated when IV TMP/SMX was available, or preshortage (PRE), were compared with patients treated when IV TMP/SMX was not available, or postshortage (POST).PRE included patients treated between September 1, 2008, and May 30, 2010, and POST included patients treated between June 1, 2010, and June 30, 2012.  

RESULTS

Thirty-six patients were included in the study, 18 in each group. Treatment failure, the primary outcome, included mortality or worsening clinical status (WCS) after at least 5 days of therapy. Three patients in PRE (16.7%) and 6 patients in POST (33.3%) experienced treatment failure (P = 0.248). No patients in PRE and 3 patients in POST (16.7%) experienced WCS (P = 0.035). Three patients in each group expired.In POST, 5 of the 6 treatment failures (83.3%) occurred during the first 6 months of the shortage. Median (interquartile range) LOS was 11 days (7-17) in PRE and 14 days (5-22) in POST (P = 0.800).In PRE, 7 patients (38.9%) were initiated on oral PJP treatment compared with 13 (72.2%) in POST (P = 0.042). 

CONCLUSIONS

The national shortage of IV TMP/SMX may have led to an immediate but temporary negative impact on treatment outcomes among HIV-infected patients with PJP at an academic medical center.Pharmacist collaboration with physicians may have helped mitigate the impact of this drug shortage on patient outcomes.  

Breaking down the barriers: challenges with development and implementation of an industry-sponsored antimicrobial stewardship data collection and analysis tool

Partnership between clinicians and the pharmaceutical industry with a focus on antimicrobial stewardship research initiatives is a necessary step toward meeting the shared goals of combating inappropriate antimicrobial use, improving patient outcomes, and minimizing resistance development. Achieving these goals requires outcomes-focused data collection and monitoring tools for antimicrobial stewardship programs (ASP) that consider real-world data about how antimicrobials are used to treat patients. Here we highlight the experiences and challenges associated with the development and implementation of an industry-sponsored electronic antimicrobial stewardship data collection and analysis tool (AS-DCAT). The benefits and risks of the industry-sponsored AS-DCAT from the perspectives of the sponsoring company and participating sites are discussed. Barriers encountered as well as general considerations and recommendations for preventing or overcoming those barriers for future studies and tool development are provided.

Vancomycin and piperacillin-tazobactam against methicillin-resistant Staphylococcus aureus and vancomycin-intermediate Staphylococcus aureus in an in vitro pharmacokinetic/pharmacodynamic model

PURPOSE

Synergy between β-lactams and vancomycin against methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-intermediate Staphylococcus aureus (VISA) has been observed in vitro and in vivo. However, studies investigating piperacillin-tazobactam with vancomycin against MRSA and VISA are limited despite broad clinical use of these antibiotics in combination. This study evaluated vancomycin and piperacillin-tazobactam against MRSA and VISA by using an in vitro pharmacokinetic/pharmacodynamic model.

METHODS

Two clinical MRSA strains (M3425 and M494) and one VISA strain (Mu50) were tested in duplicate by using a 72-hour, 1-compartment pharmacokinetic/pharmacodynamic model with the following exposures: growth control, vancomycin only, piperacillin-tazobactam only, and vancomycin with piperacillin-tazobactam. Vancomycin 1 g every 12 hours (free trough concentration, 8.75 mg/L; Cmin, 17.5 mg/L) and piperacillin-tazobactam 13.5 g per 24 hours' continuous infusion (free steady-state concentration, 27 mg/L) were simulated. Time-kill curves were constructed, and reductions in log10 CFU/mL at all time points were compared between regimens tested.

FINDINGS

Vancomycin and piperacillin-tazobactam MICs for M494, M3425, and Mu50 were 1, 1, and 4 and 1.5, 32, and >256 mg/L, respectively. All isolates had an oxacillin MIC ≥ 4 mg/L. Against all 3 isolates, vancomycin with piperacillin-tazobactam achieved a significant reduction in inoculum at 72 hours compared with vancomycin alone (all, P ≤ 0.015). The superiority of vancomycin with piperacillin-tazobactam compared with vancomycin alone became detectable at 8 hours for M3425 (P < 0.001) and at 24 hours for M494 and Mu50 (both, P ≤ 0.008). Although vancomycin with piperacillin-tazobactam achieved enhanced antibacterial activity at 72 hours against M3425 compared with vancomycin alone, bacterial regrowth occurred. Reduced susceptibility to vancomycin at 72 hours for M3425 was confirmed by using population analysis profile/AUC analysis. At 72 hours, M3425 had a PAP/AUC ratio of 0.77 compared to 0.51 at baseline.

IMPLICATIONS

Vancomycin with piperacillin-tazobactam demonstrated enhanced antimicrobial activity against MRSA and VISA compared with vancomycin alone. These results further enhance existing data that support using vancomycin in combination with a β-lactam for invasive MRSA infections. Combination therapy with vancomycin and a β-lactam against MRSA warrants clinical consideration.

Indicators for serious kidney complications associated with toxic exposures: an analysis of the National Poison Data System

CONTEXT

Over two million poisoning exposures are reported to U.S. poison control centers annually. A broad population-based survey of toxic exposures and the correlated patterns of reported kidney injury (acute or chronic) have not been systematically characterized.

OBJECTIVE

Our objective was to study the demographic and exposure patterns associated with indicators for serious kidney complications (ISKC), as defined by the variables in the NPDS.

MATERIALS AND METHODS

This was a retrospective, case-control study using the data elements available in the NPDS. We assessed data related to patient characteristics, substance exposure, and management. Cases and controls were derived from adult and pediatric exposures documented in NPDS (2001-2007) as having "renal effects." For substance-specific analyses, cases were restricted to those involving single substances or single entity pharmaceutical preparations. ISKC cases presented with one or more of the following NPDS codes: increased creatinine, and/or oliguria/anuria, and/or renal failure. Controls were subjects with "renal effects" but did not have increased creatinine, nor anuria/oliguria, nor renal failure. Univariate and multivariate logistic regression analyses identified factors associated with ISKC and determined the relationship between these factors.

RESULTS

From the approximate 16.8 million exposures reported to the NPDS within the study timeframe, there were 16,444 single substance exposures with renal effects of which 9,074 cases experienced ISKC (55.2%) compared to 7,370 controls without ISKC. Cases with ISKC tended to be males, adults, and reported to involve intentional exposures. Cases with ISKC had higher rates of reported hemodialysis/hemofiltration (27.7%; N = 2,517) and death (10.9%; N = 990) compared to controls, respectively, (2.1%; N = 155) and (0.8%; N = 60), p < 0.001. Substances considered a priori to be nephrotoxic were associated with a higher risk of ISKC.

DISCUSSION AND CONCLUSION

The NPDS provided insight into the subjects and types of exposures that associate with ISKC. Subjects with ISKC experienced higher rates of morbidity and mortality compared to subjects without ISKC. We identified subject characteristics and classes of compounds associated with ISKC. We hope that the hypotheses generated from this study of the NPDS will raise awareness of the possible risk factors and complications associated with ISKC.

Site of infection rather than vancomycin MIC predicts vancomycin treatment failure in methicillin-resistant Staphylococcus aureus bacteraemia

BACKGROUND

Therapeutic use of vancomycin is characterized by decreased susceptibilities and increasing reports of clinical failures. Few studies have examined the clinical outcomes of patients with methicillin-resistant Staphylococcus aureus (MRSA) bacteraemia treated with vancomycin. The primary objective was to compare clinical outcomes of patients with MRSA bacteraemia treated according to standard of care practices.

METHODS

Patients were included if: (i) admitted to University of New Mexico Hospital between 2002 and 2009; (ii) ≥18 years of age; (iii) had one blood culture positive for MRSA; and (iv) received vancomycin. Clinical outcomes were defined as cure, failure (relapse of infection 30 days after completion of therapy, death or change in therapy) or unevaluable. Patient demographics, source of bacteraemia, treatment regimen, and microbiological characteristics were determined.

RESULTS

Two hundred patients with MRSA bacteraemia were included. Sixty-one patients were unevaluable, leaving 139 patients for the final analysis. Seventy-two (51.8%) patients were cured and 67 (48.2%) experienced vancomycin failure. Vancomycin MIC(90) was 2 mg/L for both groups by Etest. Patients with endocarditis (P = 0.02) or pneumonia (P = 0.02) were more likely to fail therapy. Panton-Valentine leucocidin, loss of agr functionality and strain type were not predictors of outcomes in this study.

CONCLUSIONS

High failure rates were observed in patients with MRSA bacteraemia treated with vancomycin, despite high vancomycin troughs and low rates of nephrotoxicity. Predictors of vancomycin failure included endocarditis and pneumonia. In these situations, vancomycin provides suboptimal therapy.

Influence of platelets and platelet microbicidal protein susceptibility on the fate of Staphylococcus aureus in an in vitro model of infective endocarditis

Several lines of evidence indicate that platelets protect against endovascular infections such as infective endocarditis (IE). It is highly likely that a principal mechanism of this platelet host defense role is the release of platelet microbicidal proteins (PMPs) in response to agonists generated at sites of endovascular infection. We studied the ability of platelets to limit the colonization and proliferation of Staphylococcus aureus in an in vitro model of IE. Three isogenic S. aureus strains, differing in their in vitro susceptibility to thrombin-induced platelet microbicidal protein-1 (tPMP), were used: ISP479C (parental strain; highly susceptible to tPMP [tPMP(s)]); ISP479R (transposon mutant derived from ISP479; tPMP resistant [tPMP(r)]); or 757-5 (tPMP(r) transductant of the ISP479R genotype in the ISP479 parental background). Time-kill assays and in vitro IE models were used to examine the temporal relationship between thrombin-induced platelet activation and S. aureus killing. In time-kill studies, early platelet activation (30 min prior to bacterial exposure) correlated with a significant bactericidal effect against tPMP(s) ISP479C (r(2) > 0.90, P < 0.02) but not against tPMP(r) strains, ISP479R or 757-5. In the IE model, thrombin activation significantly inhibited proliferation of ISP479C within simulated vegetations compared to strains ISP479R or 757-5 (P < 0.05). The latter differences were observed despite there being no detectable differences among the three S. aureus strains in initial colonization of simulated vegetations. Collectively, these data indicate that platelets limit intravegetation proliferation of tPMP(s) but not tPMP(r) S. aureus. These findings underscore the likelihood that platelets play an important antimicrobial host defense role in preventing and/or limiting endovascular infections due to tPMP(s) pathogens.

Efficacy of LY333328 against experimental methicillin-resistant Staphylococcus aureus endocarditis

The in vivo efficacy of LY333328, a new glycopeptide antibiotic, was compared with that of vancomycin by using the rabbit model of left-sided methicillin-resistant Staphylococcus aureus endocarditis. Animals received LY333328 or vancomycin (25 mg/kg of body weight every 24 or 8 h, respectively) for 4 days. These drugs were equally effective in clearing bacteremia and in reducing bacterial counts in vegetations and tissues. We conclude that in this model, LY333328 was microbiologically effective and may be a therapeutic alternative to vancomycin.

Efficacy of trovafloxacin against experimental Staphylococcus aureus endocarditis

Trovafloxacin is a new fluoronaphthyridone chemically and functionally related to members of the fluoroquinolone class of antimicrobial agents. The in vivo efficacy of the drug was compared with that of vancomycin by using the rabbit model of left-sided endocarditis. Rabbits infected with either a nafcillin-susceptible or -resistant test strain were treated with trovafloxacin (13.3 mg/kg of body weight every 12 h) or vancomycin (25 mg/kg of body weight every 8 h) for 4 days. In comparison with untreated controls, both antimicrobial agents effectively cleared bacteremia and significantly reduced bacterial counts in vegetations and tissues of animals infected with either test strain. No resistance to trovafloxacin emerged in test strains during therapy. We conclude that in this model trovafloxacin is as efficacious as vancomycin is and may serve as a viable alternative to vancomycin for use in humans with similar infections.

Pharmacodynamics of vancomycin alone and in combination with gentamicin at various dosing intervals against methicillin-resistant Staphylococcus aureus-infected fibrin-platelet clots in an in vitro infection model

We compared the pharmacodynamic activities of vancomycin with or without gentamicin in an in vitro infection model with methicilin-resistant Staphylococcus aureus-infected fibrin-platelet clots. Infected fibrin-platelet clots (FPCs) were prepared with human cryoprecipitate, human platelets, thrombin, and the organism (approximately 10[9] CFU of MRSA-494/g) and were suspended with monofilament line in an infection model capable of simulating human pharmacokinetics. Antibiotics were bolused to simulate vancomycin regimens of 2 g every 24 h (q24h), 1 g q12h, 500 mg q6h, and continuous infusion (steady-state concentration of 20 microg/ml) and gentamicin regimens of 1.5 mg/kg of body weight q12h and 5 mg/kg once daily (q.d.). Model experiments were performed in duplicate over 72 h. FPCs were removed from the models in quadruplicate at 0, 8, 24, 32, 48, 72 h, weighed, homogenized, diluted, and plated to determine colony counts. The inoculum density at 72 h was used to compare bactericidal activities between the regimens. All regimens containing vancomycin significantly decreased the bacterial inoculum compared to the growth control (P < 0.001). Vancomycin monotherapy regimens were similar in bacterial kill regardless of dosing frequency. The addition of gentamicin (either q12h or q.d.) significantly improved the bactericidal activity of the vancomycin q6h, q12h, and q24h regimens (P < 0.001). The greatest reduction in bacterial density at 72 h (P < 0.001) and the most rapid rate of kill (time to 99.9% killing) were achieved with the regimen consisting of 2 g of vancomycin q24h plus gentamicin (q.d. or q12h).

In vitro activities of an investigational quinolone, glycylcycline, glycopeptide, streptogramin, and oxazolidinone tested alone and in combinations against vancomycin-resistant Enterococcus faecium

We evaluated the in vitro activities of clinafloxacin, CL331,002, LY333328, quinupristin dalfopristin, and eperezolid (formerly known as U-100,592) against four strains of enterococci. All regimens tested resulted in the growth inhibition of each isolate. Against the three clinafloxacin-susceptible strains, clinafloxacin tested alone was the most active treatment, decreasing the bacterial inoculum by more than 3 log10 CFU/ml after 24 h in time-kill curve studies.

Pharmacodynamic evaluation of a new glycopeptide, LY333328, and in vitro activity against Staphylococcus aureus and Enterococcus faecium

The objectives of the present study were to compare the in vitro activity of LY333328 (LY) to that of vancomycin (V) alone and in combination with gentamicin (G) and rifampin (R) against methicillin-resistant Staphylococcus aureus (MRSA) and V-resistant Enterococcus faecium (VREF), by using the killing curve methods. In addition, the effect of the inoculum size and protein on LY's activity was evaluated by using MICs and killing curves. MICs, MBCs, and killing curves were determined with supplemented Mueller-Hinton broth (B), B with albumin (4 g/dl) (A), and B with 50% pooled human serum (S). For MRSA, time to 99.9% killing after exposure to LY at four times the MIC (4x MIC) was achieved at 0.5 +/- 0 h (mean +/- standard deviation) and was significantly faster than that by V (8.54 +/- 0.10 h; P = 0.001). Against VREF, LY decreased the inoculum by 2.2 log10 CFU/ml at 24 h (P = 0.002). With a large inoculum of MRSA, the activity of LY and V at 4x MIC was decreased compared to that with the standard inoculum (P = 0.0003) and regrowth occurred at 24 h. The reduction in the number of CFU per milliliter at 24 h to 2 log10 CFU/ml was restored by increasing the LY concentration to at least 16x MIC. At 24 h, the combinations of LY and G, LY and R, LY and V, and V and G were better than either LY or V alone against a large inoculum of MRSA (P = 0.0002). LY and G achieved 99.9% killing at 1.01 +/- 0.03 h and was more rapid (P < 0.007) than all the other regimens studied except for V and G, which achieved 99.9% killing at 3.59 +/- 0.01 h. Killing curves determined with different media against a standard inoculum of MRSA did not demonstrate a significant difference between LY and V at 24 h. Time to 99.9% killing was more rapid with LY than with V in B, A, and S (P = 0.0002). Times to 99.9% killing by LY in B, A, and S were not significantly different from each other. Against VREF, LY killed better than V in B, A, or S at 24 h (P = 0.0002). LY in B was more active than LY in A or S (P = 0.0002). LY is a new potent glycopeptide with a unique activity profile. It has a greater activity than that of V against MRSA and has activity against VREF. LY demonstrated synergism in combination with gentamicin against MRSA. LY was affected by large inoculum sizes and proteins in time-kill studies. However, the effect was compensated for by increasing the drug concentration to 16x MIC.

Pharmacodynamics of RP 59500 (quinupristin-dalfopristin) administered by intermittent versus continuous infusion against Staphylococcus aureus-infected fibrin-platelet clots in an in vitro infection model

We evaluated the bactericidal activity of RP 59500 (quinupristin-dalfopristin) against fibrin-platelet clots (FPC) infected with two clinical isolates of Staphylococcus aureus, one constitutively erythromycin and methicillin resistant (S. aureus AW7) and one erythromycin and methicillin susceptible (S. aureus 1199), in an in vitro pharmacodynamic infection model. RP 59500 was administered by continuous infusion (peak steady-state concentration of 6 microg/ml) or intermittent infusion (simulated regimens of 7.5 mg/kg of body weight every 6 h (q6h) q8h, and q12h. FPCs were infected with S. aureus to achieve an initial bacterial density of 10(9) CFU/g. Model experiments were run in duplicate over 72 h. Two FPCs were removed from each model at 0, 12, 24, 36, 48, and 72 h, and the bacterial densities (in CFU per gram) were determined and compared to those of growth control experiments. Additional samples were also removed from the model over the 72-h period for pharmacokinetic evaluation. All regimens significantly (P < or = 0.01) decreased bacterial densities in the infected FPCs for both isolates compared to growth controls. This occurred even though MBCs were equal to or greater than the RP 59500 concentrations achieved in the models. There were no significant differences found between the dosing frequencies and levels of killing when examining each isolate separately. However, examination of the residual bacterial densities (CFU per gram at 72 h) and visual inspection of the overall killing effect (killing curve plots over 72 h) clearly demonstrated a more favorable bactericidal activity against 1199 than against the AW7 isolate. This was most apparent when the q8h and the q12h AW7 regimens were compared to all 1199 treatment regimens by measuring the 72-h bacterial densities (P < or = 0.01). Killing (99.9%) was not achieved against the AW7 isolate. However, a 99.9% kill was demonstrated for all dosing regimens against the 1199 isolate. The area under the concentration-time curve from 0 to 24 h was found to be significantly correlated with reduction in bacterial density for the AW7 isolate (r = 0.74, P = 0.04). No resistance was detected during any experiment for either isolate. RP 59500 efficacy against constitutively erythromycin- and methicillin-resistant S. aureus may be improved by increasing organism exposure to RP 59500 as a function of dosing frequency.