Multicenter Study of the Real-World Use of Ceftaroline versus Vancomycin for Acute Bacterial Skin and Skin Structure Infections

The objective of this study was to determine if real-world ceftaroline treatment in adults hospitalized for acute bacterial skin and skin structure infections (ABSSSI) is associated with decreased infection-related length of stay (LOSinf) compared to that with vancomycin. This was a retrospective, multicenter, cohort study from 2012 to 2017. Cox proportional hazard regression, propensity score matching, and inverse probability of treatment weighting (IPTW) were used to determine the independent effect of treatment group on LOSinf The patients were adults hospitalized with ABSSSI and treated with ceftaroline or vancomycin for ≥72 h within 120 h of diagnosis at four academic medical centers and two community hospitals in Arizona, Florida, Michigan, and West Virginia. A total of 724 patients were included (325 ceftaroline treated and 399 vancomycin treated). In general, ceftaroline-treated patients had characteristics consistent with a higher risk of poor outcomes. The unadjusted median LOSinf values were 5 (interquartile range [IQR], 3 to 7) days and 6 (IQR, 4 to 8) days in the vancomycin and ceftaroline groups, respectively (hazard ratio [HR], 0.866; 95% confidence interval [CI], 0.747 to 1.002). The Cox proportional hazard model (adjusted HR [aHR], 0.891; 95% CI, 0.748 to 1.060), propensity score-matched (aHR, 0.955; 95% CI, 0.786 to 1.159), and IPTW (aHR, 0.918; 95% CI, 0.793 to 1.063) analyses demonstrated no significant difference in LOSinf between groups. Patients treated with ceftaroline were significantly more likely to meet criteria for discharge readiness at day 3 in unadjusted and adjusted analyses. Although discharge readiness at day 3 was higher in ceftaroline-treated patients, LOSinf values were similar between treatment groups. Clinical and nonclinical factors were associated with LOSinf.

Impact of High-Level Daptomycin Resistance in the Streptococcus mitis Group on Virulence and Survivability during Daptomycin Treatment in Experimental Infective Endocarditis

Among the viridans group streptococci, the Streptococcus mitis group is the most common cause of infective endocarditis. These bacteria have a propensity to be β-lactam resistant, as well as to rapidly develop high-level and durable resistance to daptomycin (DAP). We compared a parental, daptomycin-susceptible (DAPs) S. mitis/S. oralis strain and its daptomycin-resistant (DAPr) variant in a model of experimental endocarditis in terms of (i) their relative fitness in multiple target organs in this model (vegetations, kidneys, spleen) when animals were challenged individually and in a coinfection strategy and (ii) their survivability during therapy with daptomycin-gentamicin (an in vitro combination synergistic against the parental strain). The DAPr variant was initially isolated from the cardiac vegetations of animals with experimental endocarditis caused by the parental DAPs strain following treatment with daptomycin. The parental strain and the DAPr variant were comparably virulent when animals were individually challenged. In contrast, in the coinfection model without daptomycin therapy, at both the 106- and 107-CFU/ml challenge inocula, the parental strain outcompeted the DAPr variant in all target organs, especially the kidneys and spleen. When the animals in the coinfection model of endocarditis were treated with DAP-gentamicin, the DAPs strain was completely eliminated, while the DAPr variant persisted in all target tissues. These data underscore that the acquisition of DAPr in S. mitis/S. oralis does come at an intrinsic fitness cost, although this resistance phenotype is completely protective against therapy with a potentially synergistic DAP regimen.

Novel combinations of vancomycin plus ceftaroline or oxacillin against methicillin-resistant vancomycin-intermediate Staphylococcus aureus (VISA) and heterogeneous VISA

We demonstrated a significant inverse correlation between vancomycin and beta-lactam susceptibilities in vancomycin-intermediate Staphylococcus aureus (VISA) and heterogeneous VISA (hVISA) isolates. Using time-kill assays, vancomycin plus oxacillin or ceftaroline was synergistic against 3 of 5 VISA and 1 of 5 hVISA isolates or 5 of 5 VISA and 4 of 5 hVISA isolates, respectively. Beta-lactam exposure reduced overall vancomycin-Bodipy (dipyrromethene boron difluoride [4,4-difluoro-4-bora-3a,4a-diaza-s-indacene] fluorescent dye) binding but may have improved vancomycin-cell wall interactions to improve vancomycin activity. Further research is warranted to elucidate the mechanism behind vancomycin and beta-lactam synergy.

Successful treatment of a left ventricular assist device infection with daptomycin non-susceptible methicillin-resistant Staphylococcus aureus: case report and review of the literature

Recipients of left ventricular assist devices (LVADs) are highly susceptible to the development of infections with multidrug-resistant (MDR) organisms. We describe the case of a patient with an LVAD who developed a device-related, daptomycin non-susceptible, methicillin-resistant Staphylococcus aureus infection, highlighting this patient population as highly vulnerable to the development of such antimicrobial resistance. This report includes a thorough review of the literature on the mechanisms of development of daptomycin non-susceptibility and suggests ways to prevent its emergence. We also provide and underscore the appropriate guidelines to abide by when attempting to control infections with such resistant isolates. This case also demonstrates the importance of definitive treatment with LVAD removal and transplantation as a component of appropriate management of invasive LVAD infections. In addition, we suggest that even infections with MDR organisms may not adversely affect post-transplant outcomes.

The efficacy and safety of daptomycin: first in a new class of antibiotics for Gram-positive bacteria

In the face of increasing resistance to currently available antibiotics, there is a continued interest in the development of new drugs to treat Gram-positive infections. One such agent is the cyclic lipopeptide daptomycin-licensed in the USA for treatment of Gram-positive complicated skin and skin structure infections (cSSSIs) in 2003 and currently awaiting European approval for a similar indication (complicated skin and soft tissue infections). Daptomycin exerts its rapid bactericidal effect through insertion into and subsequent depolarisation of the bacterial cell membrane, a mode of action unlike that of any other available antibiotic. This novel mechanism of action makes the development of cross-resistance between daptomycin and other antibiotic classes unlikely. Daptomycin is highly active in vitro against a range of Gram-positive pathogens, including both susceptible and multidrug-resistant staphylococci and enterococci. Bactericidal activity has also been demonstrated against both growing and stationary-phase organisms, suggesting potential utility in the treatment of deep-seated infections. Two pivotal clinical studies comparing daptomycin 4 mg/kg per day intravenously with vancomycin or oxacillin-class antibiotics demonstrated the efficacy of daptomycin for treatment of cSSSIs. Daptomycin was well tolerated, with most adverse events considered to be unrelated to study medication, of mild-to-moderate intensity, and with a frequency and distribution similar to those associated with comparator antibiotics. The favourable clinical profile and low potential for development of resistance combine to make daptomycin a promising alternative to current agents for treatment of Gram-positive bacterial infections.

Oxazolidinones: new players in the battle against multi-resistant Gram-positive bacteria

For many years the pharmaceutical industry did not pursue the development of antimicrobial agents that specifically targeted Gram-positive bacteria. Semi-synthetic penicillins and vancomycin were the mainstays of therapy for methicillin-susceptible and -resistant strains of staphylococci, respectively, as was penicillin for Streptococcus pneumoniae and beta-lactam-aminoglycoside combinations for serious enterococcal infections. In the 1980s enterococci resistant to glycopeptides emerged, followed shortly thereafter by a dissemination of penicillin-insensitive S. pneumoniae and, more recently, the occurrence of vancomycin-intermediately susceptible Staphylococcus aureus. The emergence of fully glycopeptide-resistant S. aureus is clearly on the horizon. Multi-resistant Gram-positive bacteria now pose an important therapeutic challenge for clinicians. New drugs with activity against some of these dangerous pathogens have recently been pursued, and linezolid, the first member of the oxazolidinone class, has now been licensed for clinical use in many countries. This drug has excellent in vitro and in vivo activity against all clinically relevant multi-resistant Gram-positive cocci and fills an important void in infectious disease chemotherapy.

Therapeutic options for Gram-positive infections

Gram-positive infections impose a major burden on patients and the healthcare systems globally. The need to treat these infections correctly in an empirical fashion is of paramount importance. Further complicating this changing aetiology is the emergence of resistant strains which are no longer predictably susceptible to standard first-line antimicrobials such as oxacillin or vancomycin. Thus new agents such as linezolid have been developed to assist with initial empirical prescribing in infections where Gram-positive pathogens may be present. The characteristics of linezolid, including spectrum of activity, pharmacodynamic profile, tolerablility and overall efficacy should strengthen confidence when considering initial antimicrobial therapy in patients in risk areas. Future agents also being developed to fight multi-resistant Gram-positive infections include oritavancin, daptomycin and the glycylcyclines; however, these are still in the development phase.

Activities of newer fluoroquinolones against ciprofloxacin-resistant Streptococcus pneumoniae

The incidence of ciprofloxacin resistance in Streptococcus pneumoniae is low but steadily increasing, which raises concerns regarding the clinical impact of potential cross-resistance with newer fluoroquinolones. To investigate this problem, we utilized an in vitro pharmacodynamic model and compared the activities of gatifloxacin, grepafloxacin, levofloxacin, moxifloxacin, and trovafloxacin to that of ciprofloxacin against two laboratory-derived, ciprofloxacin-resistant derivatives of S. pneumoniae (strains R919 and R921). Ciprofloxacin resistance in these strains involved the activity of a multidrug efflux pump and possibly, for R919, a mutation resulting in an amino acid substitution in GyrA. Gatifloxacin, grepafloxacin, levofloxacin, moxifloxacin, and trovafloxacin achieved 99.9% killing of both R919 and R921 in < or =28 h. With respect to levofloxacin, significant regrowth of both mutants was observed at 48 h (P < 0.05). For gatifloxacin, grepafloxacin, moxifloxacin, and trovafloxacin, regrowth was minimal at 48 h, with each maintaining 99.9% killing against both mutants. No killing of either R919 or R921 was observed with exposure to ciprofloxacin. During model experiments, resistance to gatifloxacin, grepafloxacin, moxifloxacin, and trovafloxacin did not develop but the MICs of ciprofloxacin and levofloxacin increased 1 to 2 dilutions for both R919 and R921. Although specific area under the concentration-time curve from 0 to 24 h (AUC(0--24))/MIC and maximum concentration of drug in serum (C(max))/MIC ratios have not been defined for the fluoroquinolones with respect to gram-positive organisms, our study revealed that significant regrowth and/or resistance was associated with AUC(0-24)/MIC ratios of < or =31.7 and C(max)/MIC ratios of < or =3.1. It is evident that the newer fluoroquinolones tested possess improved activity against S. pneumoniae, including strains for which ciprofloxacin MICs were elevated.

Rhodococcus equi pneumonia in a patient with human immunodeficiency virus: case report and review

Rhodococcus equi is a facultative, intracellular, gram-positive coccobacillus increasingly reported as an opportunistic pathogen in patients positive for human immunodeficiency virus (HIV). An HIV-positive man developed R. equi pneumonia and sepsis. He failed to improve despite surgical drainage of localized infection and many empiric antibiotics. Time-kill studies of R. equi isolated from the patient were performed against various antimicrobial agents to optimize therapy. Levofloxacin seemed to offer excellent in vitro bactericidal activity. Antagonism was observed with certain antibiotic combinations. Our anecdotal case report suggests that fluoroquinolones such as levofloxacin may offer superior efficacy to standard therapy in rhodococcal infections; their clinical utility deserves further investigation. In view of potential antagonism, prospective susceptibility testing for various drugs and drug combinations should be considered when clinically indicated.

Emergence of methicillin-resistant Staphylococcus aureus with intermediate glycopeptide resistance: clinical significance and treatment options

Methicillin-resistant Staphylococcus aureus is a pathogen that is associated with serious infections that pose a significant risk of morbidity and mortality because of their multidrug resistant nature. Until recently, therapeutic options were limited to vancomycin, making the use of this drug widespread. Unfortunately, the continued application of this drug has led to the emergence of glycopeptide intermediate susceptible S. aureus (GISA). By definition, these organisms demonstrated a vancomycin minimum inhibitory concentration (MIC) of >4 mg/L and <32 mg/L. However, although the mechanism of resistance is not fully elucidated at this time, GISA strains have demonstrated thickened or aggregated cell walls, an increase in penicillin binding proteins and greater autolytic activity. At present, the overall number of reported cases of GISA is relatively low. In most cases, thus far, prolonged courses of vancomycin were reported. A few cases reported monitoring serum vancomycin concentrations but because of limited information, no association with outcome can be made. Whether these GISA strains will become more widespread or evolve into fully glycopeptide resistant strains is unknown at this time. Although there are a number of new agents that possess activity against these pathogens, there is no consensus regarding specific recommendations for treatment. Strict infection control practices, routine screening for resistance and controlled use of antibacterial agents, especially vancomycin, are critical steps in preventing the further development of resistance among staphylococci.

Comparison of length of hospital stay for patients with known or suspected methicillin-resistant Staphylococcus species infections treated with linezolid or vancomycin: a randomized, multicenter trial

STUDY OBJECTIVE

To compare hospital length of stay (LOS), weekly discharges, and days of antibiotic treatment with linezolid (intravenous with oral follow-up) and vancomycin (intravenous only).

DESIGN

Multinational, randomized, phase III trial.

SETTINGS

Hospitals in North America, Latin America, and Europe.

PATIENTS

Four hundred sixty hospitalized patients with infections of known or suspected methicillin-resistant Staphylococcus species.

INTERVENTION

Administration of linezolid or vancomycin.

MEASUREMENTS AND MAIN RESULTS

For linezolid recipients, median LOS was 5 and 8 days shorter (p=0.05 and 0.003) in the complicated skin and soft tissue infection intent-to-treat (230 patients) and clinically evaluable (144) samples, and slightly but not significantly shorter in the overall intent-to-treat (460) and clinically evaluable (254) samples. In all samples, linezolid recipients had more discharges in the first week of treatment and fewer days of intravenous therapy than vancomycin recipients.

CONCLUSION

Our results support linezolid's ability to reduce medical resource use.

Activity of oritavancin (LY333328), an investigational glycopeptide, compared to that of vancomycin against multidrug-resistant Streptococcus pneumoniae in an in vitro pharmacodynamic model

In the past 2 decades, multidrug-resistant Streptococcus pneumoniae has been encountered with increasing frequency around the world. This has led to the need for newer agents in the treatment of S. pneumoniae infections. Oritavancin (LY333328) is a new glycopeptide antibiotic with activity against gram-positive organisms; however, there is limited information on the pharmacodynamics of oritavancin with respect to the treatment of S. pneumoniae. We utilized an in vitro pharmacodynamic model to compare the activity of oritavancin to that of vancomycin against two penicillin-, macrolide-, and ciprofloxacin-resistant S. pneumoniae isolates (R919 and R921) over a 48-h period. Both oritavancin and vancomycin achieved 99.9% (3-log) kill, with oritavancin achieving the limit of detection (10(2) CFU/ml) within 1 h and vancomycin achieving this limit at 24 h for both isolates. Detection of resistance was not observed for oritavancin or vancomycin during the 48-h experiments. The key pharmacodynamic parameter for oritavancin has not been well defined. In our experiment, the ratios of the area under the curve from 0 to 24 h to the MIC of oritavancin, oritavancin plus albumin, and vancomycin for both isolates were greater than 944.5, and the ratios of the maximum concentration of drug in serum to the MIC ranged from 73.7 to 7188.5. T>MIC was 100% for oritavancin and vancomycin for both isolates. Oritavancin is a unique and potent antimicrobial that warrants further investigation against multidrug-resistant S. pneumoniae.

Epidemiology, resistance, and outcomes of Acinetobacter baumannii bacteremia treated with imipenem-cilastatin or ampicillin-sulbactam

STUDY OBJECTIVE

To evaluate epidemiology, resistance, and treatment outcomes of Acinetobacter baumannii bacteremia treated with imipenem-cilastatin or ampicillin-sulbactam for 72 hours or longer.

DESIGN

Retrospective analysis.

SETTING

University teaching hospital.

PATIENTS

Forty-eight patients with A. baumannii bacteremia.

INTERVENTION

Evaluation of susceptibility and clinical data from 48 patients treated with either ampicillin-sulbactam or imipenem-cilastatin from 1987-1999.

MEASUREMENTS AND MAIN RESULTS

Comparing ampicillin-sulbactam and imipenem-cilastatin, there were no differences between days of bacteremia (4 vs 2 days, p=0.05), days to resolution of temperature or white blood cell count, success or failure during or at end of treatment, or intensive care unit total or antibiotic-related length of stay (13 vs 10 days, p=0.05). Patients treated with ampicillin-sulbactam had significantly decreased antibiotic treatment costs (1500 dollars vs 500 dollars, p=0.004).

CONCLUSION

Ampicillin-sulbactam is at least as effective as imipenem-cilastatin based on clinical response at days 2, 7, and end of treatment and is a cost-effective alternative for treatment of A. baumannii infections.

Bactericidal activities of two daptomycin regimens against clinical strains of glycopeptide intermediate-resistant Staphylococcus aureus, vancomycin-resistant Enterococcus faecium, and methicillin-resistant Staphylococcus aureus isolates in an in vitro pharmacodynamic model with simulated endocardial vegetations

Daptomycin is an investigational lipopeptide antibiotic active against gram-positive organisms. The mechanism of action is unique, resulting in interference with cell membrane transport. The bactericidal activity of daptomycin was evaluated against glycopeptide-intermediate susceptible Staphylococcus aureus (GISA), vancomycin-resistant Enterococcus faecium (VREF), and methicillin-resistant S. aureus (MRSA) in an in vitro infection model with simulated endocardial vegetations. Simulated regimens of daptomycin at 6 mg/kg/day (D6) and 10 mg/kg/day (D10) were utilized. MICs and MBCs for daptomycin were determined in the absence and in the presence of albumin with the following results (MIC/MBC): for GISA-992, 0.5/1.0 and 16/16; for VREF-590, 2.0/2.0 and 32/32; and for MRSA-494, 0.25/0.25 and 1.0/4.0 microg/ml, respectively. During the first 8 h daptomycin significantly reduced the inoculum for all organisms. Daptomycin at 6 mg/kg/day and 10 mg/kg/day had log(10) CFU/g reductions of 5 and 6, 3.4 and 5, and 6.4 and 6.5 by 8 h for GISA-992, VREF-590, and MRSA-494, respectively. Against both GISA-992 and VREF-590, the D10 regimen achieved the limit of detection at 72 h, with D6 regimens showing slight regrowth. A concentration-dependent killing effect was noted to occur, with daptomycin demonstrating a more rapid and greater kill from the D10 versus the D6 regimen. The results of this study suggest that daptomycin demonstrates significant (P < 0.05) activity against gram-positive organisms in a simulated sequestered infection site.

Activities of LY333328 and vancomycin administered alone or in combination with gentamicin against three strains of vancomycin-intermediate Staphylococcus aureus in an in vitro pharmacodynamic infection model

Staphylococcus aureus with intermediate glycopeptide susceptibility (glycopeptide-intermediate S. aureus [GISA]) has been isolated from patients with apparent therapy failures. We studied the killing activity of vancomycin over a range of simulated conventional doses (1 to 1.5 g every 12 h) against three of these GISA strains in an in vitro pharmacodynamic infection model. We also studied the activity of a new glycopeptide (LY333328) at a simulated dose of 3 mg/kg of body weight every 24 h or 5 mg/kg every 24 h, as well as the potential for vancomycin and gentamicin synergy against these GISA strains. Four doses of vancomycin with or without gentamicin or two doses of LY333328 were administered over the 48-h study period. The vancomycin and LY333328 MICs and minimal bactericidal concentrations (MBCs) for the three GISA strains (strains 14379, 992, and Mu50) were 8 and 8 microgram/ml and 1 and 2 microgram/ml, respectively, for GISA 14379, 6 and 6 microgram/ml and 1 and 1 microgram/ml, respectively, for GISA 992, and 8 and 12 microgram/ml and 2 and 8 microgram/ml, respectively, for GISA Mu50. Vancomycin and LY333328 MICs and MBCs were 0.75 and 1.0 microgram/ml and 1 and 1 microgram/ml, respectively for a vancomycin-susceptible comparator strain (methicillin-resistant S. aureus [MRSA] 494). The addition of albumin to the growth medium increased the LY333328 MICs and MBCs approximately 8- to 16-fold. Vancomycin was bacteriostatic against the three GISA strains at doses of 1, 1.125, and 1.25 g every 12 h. Vancomycin was bactericidal at the dose of 1.5 g every 12 h against all strains; bactericidal activity occurred against the GISA strains at 8- to 10-fold lower ratios of the peak concentration to the MIC and the area under the concentration-time curve from time zero to 24 h (AUC(0-24)) to the MIC compared to those for the vancomycin-sensitive control strain. Overall, vancomycin activity was significantly correlated with the AUC(0-24) (R(2) = 0.79; P < 0.001) by multiple stepwise regression analyses. The addition of gentamicin did not significantly affect killing activity against any strain. LY333328 was bactericidal against GISA strains 14379 and 992 and against MRSA 494 only with the 5-mg/kg/day dose simulations. The higher dose of LY333328 also prevented regrowth over the 48-h experiments for all strains tested. Higher doses of vancomycin (1.5 g every 12 h) and LY333328 (5 mg/kg every 24 h) may represent potential treatment options for infections caused by GISA strains.

Once-daily aminoglycoside in the treatment of Enterococcus faecalis endocarditis: case report and review

Once-daily administration of aminoglycosides (ODA) is effective and safe for many indications. By optimizing pharmacodynamic principles, it enhances bactericidal activity and minimizes toxicity. Its use for the treatment of enterococcal infection is controversial, however, and results of in vitro studies and animal models of endocarditis are conflicting. To date, no case reports or clinical trials have examined its utility in human enterococcal endocarditis. A patient with right-sided endocarditis caused by Enterococcus faecalis was managed by once-daily gentamicin. Clinical and bacteriologic cures of this patient raise questions as to whether enterococcal endocarditis should be regarded as contraindication to ODA. The clinical utility of ODA in this disease deserves further investigation.

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.

In vitro activities of daptomycin, arbekacin, vancomycin, and gentamicin alone and/or in combination against glycopeptide intermediate-resistant Staphylococcus aureus in an infection model

Daptomycin, a lipopeptide antibiotic, has broad activity against gram-positive organisms, similar to vancomycin; however, its mechanism of action differs, resulting in interference with cell membrane transport and a more rapid bactericidal activity. In light of increasing need for alternative treatments against intermediate-resistant Staphylococcus aureus, there is revitalized interest in this antibiotic. We, therefore, evaluated the activity of daptomycin alone or in combination in an in vitro infection model against two glycopeptide intermediate-resistant S. aureus (GISA) isolates. Newly designed regimens of daptomycin at 4 and 6 mg/kg of body weight every 24 h (q24h) were compared to the previous regimen of 3 mg/kg q12h. Daptomycin MICs and minimal bactericidal concentrations (MBCs) (MIC/MBC) for Mu-50, HIP5836 (992), and MRSA-67 were 0.5/1.0, 0.5/1.0, and 0.125/0.5 microgram/ml, respectively. MICs and MBCs of arbekacin for the three strains were 2.0/8.0, 0. 125/0.5, and 0.125/0.25 microgram/ml, respectively. Vancomycin and gentamicin MICs and MBCs for the three strains were 8.0/8.0, 8.0/8.0, and 0.5/1.0 microgram/ml and 128/128, 0.5/1.0, and 0.25/0.5 microgram/ml, respectively. Our experience with daptomycin in an in vitro infection model has shown significant kill against the two GISA strains (Mu-50 and 992) (P < 0.03). We also noted that kill was related to a total dose effect for 992, in which simulated daptomycin in vivo dosages of 6 mg/kg q24h and 3 mg/kg q12h produced similar kill and 4 mg/kg q24h resulted in significant regrowth (P </= 0.05). Combination therapy with arbekacin resulted in synergistic activity against Mu-50. Daptomycin area under the concentration-time curve/MIC and C(max)/MIC ranges for GISA isolates were 80 to 116 and 6 to 12, respectively, and ranges for MRSA-67 were 320 to 461 and 24 to 48, respectively, and appeared to have an association with kill (i.e., decreased CFU/milliliter) at 24 and 48 h. Therefore, these experiments suggest that daptomycin alone or in combination could provide an alternative for the treatment of GISA.

Comparison of a rabbit model of bacterial endocarditis and an in vitro infection model with simulated endocardial vegetations

Animal models are commonly used to determine the efficacy of various antimicrobial agents for treatment of bacterial endocarditis. Previously we have utilized an in vitro infection model, which incorporates simulated endocardial vegetations (SEVs) to evaluate the pharmacodynamics of various antibiotics. In the present study, we compared four experimental rabbit endocarditis protocols to an in vitro infection model in an effort to determine if these models are comparable. We have evaluated the activity of clinafloxacin, trovafloxacin, sparfloxacin, and ciprofloxacin in rabbit models against Staphylococcus aureus and Enterococcus spp. In vitro models were performed simulating the antibiotic pharmacokinetics obtained in the in vivo studies. Models were dosed the same as rabbit models, and SEVs were evaluated at the same time the rabbit vegetations were examined. Clinafloxacin and trovafloxacin were evaluated against methicillin-susceptible (MSSA1199) and -resistant (MRSA494) strains of S. aureus. Ciprofloxacin was studied against MSSA1199 and MSSA487. Sparfloxacin and clinafloxacin were evaluated against Enterococcus faecium SF2149 and Enterococcus faecalis WH245, respectively. We found that reductions in SEV bacterial density obtained in the in vitro model were similar to those obtained in rabbit vegetations, indicating that the SEV model may be a valuable tool for assessing antibiotic potential in the treatment of bacterial endocarditis.

Pharmacodynamics of vancomycin and ampicillin alone and in combination with gentamicin once daily or thrice daily against Enterococcus faecalis in an in vitro infection model

We compared the pharmacodynamic activities of vancomycin and ampicillin with or without gentamicin once daily or thrice daily in an in vitro infection model with fibrin-platelet clots (FPCs) infected with Enterococcus faecalis. Antibiotics were administered as a bolus to simulate human pharmacokinetics with regimens consisting of vancomycin 1 g q12h, ampicillin 2 g q6h and gentamicin 1.3 mg/kg q8h and 5 mg/kg qd. Model experiments were performed in duplicate over 72 h. FPCs were removed from the models in triplicate at 0, 8, 24, 32, 48 and 72 h, weighed, homogenized, diluted and plated to determine colony counts. Additional FPCs were removed at over 72 h post-antibiotic dose to determine antibiotic concentrations. The inoculum density at 72 h was used to compare bactericidal activity between the regimens. Overall, all antibiotic regimens containing either ampicillin or vancomycin significantly (P < 0.01) decreased the bacterial load at 72 h compared with the growth control although monotherapy regimens with either vancomycin or gentamicin had little impact. Ampicillin was superior to vancomycin with or without the addition of gentamicin (P < 0.01). There were no significant differences in reduction of bacterial density at 72 h between the combination of ampicillin or vancomycin plus gentamicin q8h and ampicillin or vancomycin plus gentamicin once daily. This was despite achieving unmeasurable FPC gentamicin concentrations after the 8 h time point during the once-daily aminoglycoside regimen. Vancomycin plus gentamicin either every 8 h or once daily was significantly (P < 0.01) better than vancomycin alone. Ampicillin plus either of the two gentamicin regimens was also better than ampicillin alone but this did not reach statistical significance. Our data suggest that once-daily gentamicin in combination with ampicillin or vancomycin demonstrates equivalent bacterial reductions to combination therapy with thrice-daily gentamicin. Once-daily aminoglycoside combination therapy for the treatment of enterococcal endocarditis warrants further investigation.

Activities of trovafloxacin and ampicillin-sulbactam alone or in combination versus three strains of vancomycin- intermediate Staphylococcus aureus in an in vitro pharmacodynamic infection model

The recent isolation of clinical strains of methicillin-resistant Staphylococcus aureus (MRSA) with intermediate susceptibility (MICs, 8 microg/ml) to vancomycin (vancomycin-intermediate S. aureus [VISA]) emphasizes the importance of developing novel antimicrobial regimens and/or agents for future treatment. We studied the activities of ampicillin-sulbactam and trovafloxacin alone or in combination against three unique strains of VISA in an in vitro infection model. Two VISA strains were trovafloxacin susceptible (MICs, < or =2 microg/ml); one VISA strain was trovafloxacin resistant (MIC, 4 microg/ml). Trovafloxacin was administered to simulate a dose of 200 or 400 mg every 24 h. Ampicillin-sulbactam was administered to simulate a dose of 3 g every 6 h. Samples were removed from the infection models over 48 h, and reductions in colony counts were compared between regimens. Trovafloxacin (200 mg) produced rapid killing of a control MRSA strain over the 48-h experiment but produced only slight killing of all three VISA strains. The higher dose of trovafloxacin improved killing but did not produce bactericidal activity at 48 h. Ampicillin-sulbactam produced rapid bactericidal activity against all four strains tested, and colony counts at 8 h were at the limits of detection. However, regrowth occurred by 48 h for each strain. The combination of ampicillin-sulbactam and trovafloxacin provided additive activity against two of the three VISA strains. In conclusion, trovafloxacin or ampicillin-sulbactam alone did not provide adequate activity against the VISA strains for the 48-h evaluation period, but the combination could help improve activity against some strains of VISA.

Pharmacokinetics and pharmacodynamics of ceftizoxime in patients with dosages adjusted for renal function

STUDY OBJECTIVE

Our institution developed dosing guidelines for patients with renal impairment based on pharmacokinetic data and class-specific pharmacodynamics. Ceftizoxime was chosen as a model agent to evaluate if the modified guidelines achieved similar minimal plasma concentration (Cp(min)) and time above the minimum inhibitory concentration of the infecting organism (T>MIC) in patients with renal impairment versus those with normal renal function.

DESIGN

Prospective pharmacokinetic and pharmacodynamic evaluation of ceftizoxime dosages.

SETTING

University-affiliated hospital.

PATIENTS

Forty-three patients with suspected or documented infection were enrolled and classified into four groups based on creatinine clearance (Cl(cr); ml/min): group 1, above 100; group 2, 61-99; group 3, 31-60; and group 4, 15-30.

INTERVENTIONS

Ceftizoxime serum concentrations were obtained at steady state.

MEASUREMENTS AND MAIN RESULTS

Pharmacokinetic and pharmacodynamic parameters were calculated. As expected, clearance and elimination rate constant were reduced, and half-life tended to be greater in patients with renal impairment. The Cp(min) and area under the concentration-time curve over 24 hours were similar between groups (p=0.39, p=0.42). The T>MIC was 100% for all patient isolates, and 90% or more versus our clinical strain for all groups. Clinical outcomes were similar among all groups.

CONCLUSION

Our dosing guidelines achieved similar Cp(min) among all groups of patients. Our results support that recommendations for dosing adjustments should be based on pharmacokinetic data and must also consider pharmacodynamic parameters.

In vitro activities of daptomycin, vancomycin, linezolid, and quinupristin-dalfopristin against Staphylococci and Enterococci, including vancomycin- intermediate and -resistant strains

The in vitro activity of daptomycin was compared with those of vancomycin, linezolid, and quinupristin-dalfopristin against a variety (n = 203) of gram-positive bacteria, including methicillin-resistant Staphylococcus aureus and S. epidermidis (MRSA and MRSE, respectively), vancomycin-resistant enterococci (VRE), and vancomycin-intermediate S. aureus (VISA). Overall, daptomycin was more active against all organisms tested, except Enterococcus faecium and VISA, against which its activity was similar to that of quinupristin-dalfopristin. In time-kill studies with MRSA, MRSE, VRE, and VISA, daptomycin demonstrated greater bactericidal activity than all other drugs tested, killing > or =3 log CFU/ml by 8 h. Daptomycin may be a potential alternative drug therapy for multidrug-resistant gram-positive organisms and warrants further investigation.

Activities of trovafloxacin, gatifloxacin, clinafloxacin, sparfloxacin, levofloxacin, and ciprofloxacin against penicillin-resistant Streptococcus pneumoniae in an in vitro infection model

We adapted an in vitro pharmacodynamic model of infection to incorporate infected fibrin clots. The bactericidal activities of various fluoroquinolones against two strains of penicillin-resistant Streptococcus pneumoniae were studied over a 48-h period. Bacteria were prepared in Muller-Hinton broth by using colonies from a 24-h tryptic soy agar plus 5% sheep blood plate and were added to a mixture of cryoprecipitate (80%) and thrombin (10%) to achieve approximately 10(6) CFU of organism per fibrin clot. The fibrin clots were suspended into the models and removed, in triplicate, at various time points over 48 h. Control models were also conducted to characterize the growth of S. pneumoniae in the growth medium without antibiotic. Trovafloxacin, gatifloxacin, clinafloxacin, sparfloxacin, levofloxacin, and ciprofloxacin were administered to simulate their pharmacokinetic profiles in humans. Fibrin clot samples were also plated onto antibiotic-containing tryptic soy agar plus 5% lysed horse blood to detect resistance. The newer fluoroquinolones demonstrated better activity than ciprofloxacin against both isolates. In conclusion, the newer quinolones demonstrated significant activity against penicillin-resistant S. pneumoniae, with standard dosing resulting in area under the concentration-time curve/MIC ratios and peak concentration/MIC ratios that resulted in 99.9% killing against these isolates.

Pharmacodynamic characterization of nephrotoxicity associated with once-daily aminoglycoside

STUDY OBJECTIVE

To characterize nephrotoxicity associated with an individualized serum concentration target-specific, once-daily aminoglycoside (ODA) program.

DESIGN

Concurrent and retrospective study.

SETTING

University-affiliated trauma hospital.

PATIENTS

Two hundred patients treated with ODA and 100 treated with individualized traditional dosing (TDA).

INTERVENTIONS

Empiric dosing for both groups was based on patient-specific pharmacokinetics and severity of infection. Regimens were modified according to predetermined target maximum and minimum serum concentrations for both groups.

MEASUREMENTS AND MAIN RESULTS

Nephrotoxicity occurred in 7.5% patients treated with ODA and 14.7% receiving TDA (p=0.05). Minimum serum concentrations, length of aminoglycoside therapy, and cumulative area under the curve (AUC) were all dependently related to nephrotoxicity, and concomitant vancomycin and other nephrotoxic drugs were independently related to the disorder. The cumulative AUC was greatest in patients receiving TDA (p=0.03), and the modeled probability of becoming toxic at any given cumulative AUC was significantly greater with TDA than with ODA (p<0.01). Clinical and microbiologic outcomes were similar between groups. Maximum concentration:minimum inhibitory concentration ratios were higher (p<0.01) and number of days to organism eradication was shorter in the ODA group (p=0.04).

CONCLUSION

The trend was toward decreased nephrotoxicity in patients treated with ODA compared with TDA, and at any given cumulative AUC, the risk of toxicity was lower for ODA.

Pharmacologic and bacteriologic properties of SCH-27899 (Ziracin), an investigational antibiotic from the everninomicin family

SCH-27899 is an investigational antibiotic from the everninomicin family, a group of oligosaccharide antibiotics produced by Micromonospora carbonacea. Information regarding the pharmacology, pharmacodynamics, pharmacokinetics, efficacy, and toxicity of this agent was obtained from a MEDLINE search and a review of abstracts presented at recent scientific meetings. SCH-27899 has in vitro bacteriostatic activity against a wide variety of gram-positive organisms, including highly resistant organisms such as methicillin-resistant Staphylococcus aureus, vancomycin-intermediate-sensitivity S. aureus, Streptococcus pneumoniae (both penicillin-susceptible and -nonsusceptible), and vancomycin-resistant enterococci. In vitro data, animal studies, and preliminary human studies indicate that it is effective and fairly well tolerated. Its place in therapy remains to be determined, and clinical trials continue.

Evaluation of Acinetobacter baumannii infection and colonization, and antimicrobial treatment patterns in an urban teaching hospital

In 1990 there was a sudden increase in the incidence of colonization and infection due to Acinetobacter baumannii (AB) in our intensive care units (ICUs). The isolates were multiply resistant to beta-lactam and aminoglycoside antibiotics, but remained susceptible to imipenem, amikacin, and ampicillin-sulbactam. We examined the frequency of infection and colonization with AB and the effects of increased imipenem and amikacin therapy on Pseudomonas aeruginosa. We also used disease-matched controls to determine the clinical and financial impacts of treating colonization. All patients with at least one AB isolate from January-December 1992 were identified retrospectively and classified as infected or colonized based on published Centers for Disease Control criteria; the control group was selected from a computerized medical records data base matching primary diagnostic codes (102 patients both groups). The 102 patients yielded 140 isolates, 124 resistant AB and 16 sensitive AB. Thirty three patients were infected, 69 colonized. Mortality correlated with APACHE II scores. Patients acquired the organism approximately 2 weeks after admission; they had a mean ICU stay of 27.35 days, compared with 5.53 days for controls. Patients with positive AB cultures required significantly more use of ventilators than those with negative AB cultures. They also had significantly longer hospital stay, more bed transfers, greater duration and number of antibiotics, and higher hospital and pharmacy charges. Unnecessary treatment for colonization with either imipenem or amikacin resulted in a substantial decrease of P. aeruginosa susceptibility to each agent. The financial impact of treating colonization was significant and is a potential area for cost avoidance. Our results emphasize the need to extubate and move patients to non-ICU beds as soon as possible to decrease the risk of nosocomial infection. It also highlights the need to avoid treating colonization, thus avoiding unnecessary antibiotic therapy.

The effects of NorA inhibition on the activities of levofloxacin, ciprofloxacin and norfloxacin against two genetically related strains of Staphylococcus aureus in an in-vitro infection model

NorA is a membrane-associated multidrug efflux protein that can decrease susceptibility to fluoroquinolones in Staphylococcus aureus. We have previously determined that NorA inhibition can increase fluoroquinolone killing activity and post-antibiotic effect. In the current investigation, we studied the killing activity and development of resistance for levofloxacin, ciprofloxacin and norfloxacin with or without the H+/K+ ATPase inhibitor omeprazole, in a wild-type strain of S. aureus (SA-1199) and its NorA hyperproducing mutant (SA-1199-3) in an in-vitro pharmacodynamic model with infected fibrin-platelet matrices. Each drug was administered every 12-24 h for 72 h and human pharmacokinetics were simulated. Levofloxacin was the most potent fluoroquinolone against both strains and its activity was not significantly affected by combination with omeprazole. The addition of omeprazole to ciprofloxacin significantly lowered colony counts at all time-points against both strains and decreased the time to 99.9% kill from 72.2 h to 33.8 h against SA-1199. The addition of omeprazole minimally increased norfloxacin activity against both strains. Omeprazole decreased the frequency of ciprofloxacin resistance nearly 100-fold at the 24 h time-point, but the frequency of resistance was not significantly different for any of the fluoroquinolone regimens after this time-point. No resistance was detected during levofloxacin regimens. The hydrophobic fluoroquinolones such as levofloxacin appear to circumvent NorA efflux, which may contribute to their better activity and decreased resistance rates against staphylococci. More durable and potent NorA inhibitor compounds are needed that can improve killing activity and prevent resistance.

Analysis of vancomycin population susceptibility profiles, killing activity, and postantibiotic effect against vancomycin-intermediate Staphylococcus aureus

Methicillin-resistant Staphylococcus aureus strains with decreased vancomycin susceptibility have been isolated from patients in the United States and Japan. The impact of decreased vancomycin susceptibility on the drug's pharmacodynamic parameters has not been addressed. We studied the activity of vancomycin against three clinical strains of vancomycin intermediate-susceptible Staphylococcus aureus (VISA) under high- and low-inoculum conditions, with stationary- and logarithmic-growth-phase kill curves, and in postantibiotic effect (PAE) experiments. We also investigated the stability of the decreased vancomycin susceptibility by using population susceptibility profiles. The respective vancomycin microdilution MICs and MBCs for VISA strains HIP5836, 14379, and Mu50 were 8 and 8, 8 and 8, and 8 and 16 microg/ml. HIP5836 had the most homogeneous elevation of vancomycin MICs, because the MIC for nearly all bacteria in the inoculum was 8 microg/ml. The population MICs (defined as the lowest vancomycin concentration inhibiting 99. 9% of growth) for the first serial passages of HIP5836, Mu50, and 14379 were 8, 4, and 2 microg/ml, respectively. After 10 passages, they decreased to 4, 2, and 1 microg/ml, respectively. The Mu50 population MIC increased to 12 microg/ml after five serial passages on vancomycin agar. In the low- and high-inoculum kill curves, time to 99.9% killing was significantly (P < 0.05) longer for both Mu50 and HIP5836 than that for 14379 and a control strain. However, colony counts at 24 h were similar to those of the vancomycin-sensitive strain for all VISA strains. The PAE (at 4x MIC) ranged from 1.3 h for 14379 to 2.0 h for HIP5836 and was similar to or greater than the PAE against the vancomycin-sensitive strain. In conclusion, we found that the decreased vancomycin susceptibility increased during persistent exposures to the drug and decreased upon removal of the selective pressure. The decreased vancomycin susceptibility decreased the rate of vancomycin killing, but did not affect the extent of killing or the PAE.

Prospective evaluation of the effect of an aminoglycoside dosing regimen on rates of observed nephrotoxicity and ototoxicity

The nephrotoxicity and ototoxicity associated with once-daily versus twice-daily administration of aminoglycosides was assessed in patients with suspected or proven gram-negative bacterial infections in a randomized, double-blind clinical trial. Patients who received therapy for >/=72 h were evaluated for toxicity. Patients also received concomitant antibiotics as deemed necessary for treatment of their infection. Plasma aminoglycoside concentrations, prospective aminoglycoside dosage adjustment, and serial audiologic and renal status evaluations were performed. The probability of occurrence of a nephrotoxic event and its relationship to doses and daily aminoglycoside exposure served as the main outcome measurement. One hundred twenty-three patients were enrolled in the study, with 83 patients receiving therapy for at least 72 h. For 74 patients plasma aminoglycoside concentrations were available for analysis, and the patients formed the group evaluable for toxicity. The primary infectious diagnosis for the patients who were enrolled in the study were bacteremia or sepsis, respiratory infections, skin and soft tissue infections, or urosepsis or pyelonephritis. Of the 74 patients evaluable for toxicity, 39 received doses twice daily and 35 received doses once daily and a placebo 12 h later. Nephrotoxicity occurred in 6 of 39 (15.4%) patients who received aminoglycosides twice daily and 0 of 35 patients who received aminoglycosides once daily. The schedule of aminoglycoside administration, concomitant use of vancomycin, and daily area under the plasma concentration-time curve (AUC) for the aminoglycosides were found to be significant predictors of nephrotoxicity by multivariate logistic regression analysis (P Collapse

Key Words Collapse

MESH Headings

• Adult
• Aged
• Aged, 80 and over
• Aminoglycosides
• Anti-Bacterial Agents/administration & dosage
• Anti-Bacterial Agents/adverse effects
• Anti-Bacterial Agents/pharmacokinetics
• Double-Blind Method
• Drug Administration Schedule
• Female
• Hearing/drug effects
• Humans
• Kidney/drug effects
• Male
• Middle Aged
• Prospective Studies

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Grants Collapse

Affiliation(s)

M J Rybak The Anti-Infective Research Laboratory, Department of Pharmacy Services, Detroit Receiving Hospital and University Health Center, College of Pharmacy and Allied Health Professions, Wayne State University, Detroit, Michigan 48201, USA.
B J Abate
S L Kang
M J Ruffing
S A Lerner
G L Drusano

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Vancomycin-Resistant Enterococcus: Infectious Endocarditis Treatment

Vancomycin-resistant Enterococcus species represent serious gram-positive pathogens for which there is currently no recommended therapy. There are a number of new antibiotics with activity against these pathogens in development. Although there is a great deal of experience with some of these agents for skin and soft tissue infections, bacteremia, pneumonia, and intra-abdominal infections, there is currently little information available for the treatment of endocarditis. Animal and limited human data thus far suggest that new agents such as quinuprisitin-dalfopristin, LY333328 (a new glycopeptide antibiotic), and daptomycin (a lipopeptide antibiotic) may prove useful for this indication. Additional information, and especially combination treatment, are warranted to improve success and limit the emergence of resistance to these new antibiotics.

Evaluation of bactericidal activities of LY333328, vancomycin, teicoplanin, ampicillin-sulbactam, trovafloxacin, and RP59500 alone or in combination with rifampin or gentamicin against different strains of vancomycin-intermediate Staphylococcus aureus by time-kill curve methods

This in vitro study evaluated the activities of vancomycin, LY333328, and teicoplanin alone and in combination with gentamicin, rifampin, and RP59500 against Staphylococcus aureus isolates with intermediate susceptibilities to vancomycin. Ampicillin-sulbactam and trovafloxacin were also evaluated. LY333328 and ampicillin-sulbactam resulted in bactericidal activity against all isolates. The combination of gentamicin with glycopeptides showed synergistic activity, while rifampin had no added benefit.

Outcome assessment of minimizing vancomycin monitoring and dosing adjustments

An approach to minimize monitoring of vancomycin therapy was evaluated in 120 patients, and results were compared with data from 120 patients in whom vancomycin therapy was monitored and adjusted based on serum peak and trough concentrations and traditional pharmacokinetic methods. Patients dosed by the nomogram (NM) had regimens adjusted based on actual body weight, estimated creatinine clearance, and a targeted trough concentration of 5-20 microg/ml. A single trough serum concentration was drawn only after 5 or more days of therapy. Overall, the average length of therapy was similar between groups (9.9 +/- 9.4 days NM and 8.6 +/- 7.2 days pharmacokinetic). The most common regimen for both groups was 1 g every 12 hours, although NM patients received significantly fewer grams/day (1.9 +/- 0.7 g/day) than the pharmacokinetic group (2.2 +/- 1.0 g/day, p<0.04). Patients dosed by NM also had significantly fewer regimen changes (0.63 +/- 0.96 vs pharmacokinetic 0.92 +/- 0.97, p=0.02) as well as significantly fewer serum concentrations measured/patient (1.08 +/- 1.9 vs 1.96 +/- 2.0, p=0.001). In addition, serum concentrations for NM patients were drawn later in therapy (5.4 +/- 2.5 vs 3.8 +/- 3.4 days, p=0.004). Of patients dosed by NM guidelines, 77 had trough concentrations drawn; these data were used to validate the nomogram. Seventy-two patients (94%) had trough concentrations in the target range of 5-20 microg/ml. No differences were found between groups with respect to cure, improvement, failure, or days to eradication, or with respect to nephrotoxicity. Finally, total drug cost/patient was not different between groups. A considerable cost savings to our institution was noted for patients dosed by NM compared with pharmacokinetics ($232.5 +/- 50.74 vs $403.75 +/- 70.97/mo, p=0.009) based on levels saved. Caution should be applied when generalizing our results to other patient populations.

Effects of NorA inhibitors on in vitro antibacterial activities and postantibiotic effects of levofloxacin, ciprofloxacin, and norfloxacin in genetically related strains of Staphylococcus aureus

NorA is a membrane-associated multidrug efflux protein that can decrease susceptibility to fluoroquinolones in Staphylococcus aureus. To determine the effect of NorA inhibition on the pharmacodynamics of fluoroquinolones, we evaluated the activities of levofloxacin, ciprofloxacin, and norfloxacin with and without various NorA inhibitors against three genetically related strains of S. aureus (SA 1199, the wild-type; SA 1199B, a NorA hyperproducer with a grlA mutation; and SA 1199-3, a strain that inducibly hyperproduces NorA) using susceptibility testing, time-kill curves, and postantibiotic effect (PAE) methods. Levofloxacin had the most potent activity against all three strains and was minimally affected by addition of NorA inhibitors. In contrast, reserpine, omeprazole, and lansoprazole produced 4-fold decreases in ciprofloxacin and norfloxacin MICs and MBCs for SA 1199 and 4- to 16-fold decreases for both SA 1199B and SA 1199-3. In time-kill experiments reserpine, omeprazole, or lansoprazole increased levofloxacin activity against SA 1199-3 alone by 2 log10 CFU/ml and increased norfloxacin and ciprofloxacin activities against all three strains by 0.5 to 4 log10 CFU/ml. Reserpine and omeprazole increased norfloxacin PAEs on SA 1199, SA 1199B, and SA 1199-3 from 0.9, 0.6, and 0.2 h to 2.5 to 4.5, 1.1 to 1.3, and 0.4 to 1.1 h, respectively; similar effects were observed with ciprofloxacin. Reserpine and omeprazole increased the levofloxacin PAE only on SA 1199B (from 1.6 to 5.0 and 3.1 h, respectively). In conclusion, the NorA inhibitors dramatically improved the activities of the more hydrophilic fluoroquinolones (norfloxacin and ciprofloxacin). These compounds may restore the activities of these fluoroquinolones against resistant strains of S. aureus or may potentially enhance their activities against sensitive strains.

Treatment of vancomycin-resistant Enterococcus faecium with RP 59500 (quinupristin-dalfopristin) administered by intermittent or continuous infusion, alone or in combination with doxycycline, in an in vitro pharmacodynamic infection model with simulated endocardial vegetations

Quinupristin-dalfopristin is a streptogramin antibiotic combination with activity against vancomycin-resistant Enterococcus faecium (VREF), but emergence of resistance has been recently reported. We studied the activity of quinupristin-dalfopristin against two clinical strains of VREF (12311 and 12366) in an in vitro pharmacodynamic model with simulated endocardial vegetations (SEVs) to determine the potential for resistance selection and possible strategies for prevention. Baseline MICs/minimal bactericidal concentrations (microg/ml) for quinupristin-dalfopristin, quinupristin, dalfopristin, and doxycycline were 0.25/2, 64/>512, 4/512, and 0.125/8 for VREF 12311 and 0.25/32, 128/>512, 2/128, and 0.25/16 for VREF 12366, respectively. Quinupristin-dalfopristin regimens had significantly less activity against VREF 12366 than VREF 12311. An 8-microg/ml simulated continuous infusion was the only bactericidal regimen with time to 99.9% killing = 90 hours. The combination of quinupristin-dalfopristin every 8 h with doxycycline resulted in more killing compared to either drug alone. Quinupristin-dalfopristin-resistant mutants (MICs, 4 microg/ml; resistance proportion, approximately 4 x 10(-4)) emerged during the quinupristin-dalfopristin monotherapies for both VREF strains. Resistance was unstable in VREF 12311 and stable in VREF 12366. The 8-microg/ml continuous infusion or addition of doxycycline to quinupristin-dalfopristin prevented the emergence of resistance for both strains over the 96-h test period. These findings replicated the development of resistance reported in humans and emphasized bacterial factors (drug susceptibility, high inoculum, organism growth phase) and infectious conditions (penetration barriers) which could increase chances for clinical resistance. The combination of quinupristin-dalfopristin with doxycycline and the administration of quinupristin-dalfopristin as a high-dose continuous infusion warrant further study to determine their potential clinical utility.

Pharmacodynamic analysis of the activity of quinupristin-dalfopristin against vancomycin-resistant Enterococcus faecium with differing MBCs via time-kill-curve and postantibiotic effect methods

Quinupristin-dalfopristin (Q-D) is a new water-soluble, semisynthetic antibiotic that is derived from natural streptogramins and that is combined in a 30:70 ratio. A number of studies have described the pharmacodynamic properties of this drug, but most have investigated only staphylococci or streptococci. We evaluated the relationship between Q-D, quinupristin (Q), and/or dalfopristin (D) susceptibility parameters and antibacterial activities against 22 clinical isolates of vancomycin-resistant Enterococcus faecium (VREF) by using the concentration-time-kill-curve method and by measuring postantibiotic effects. Q-D, Q, and D MICs and minimum bactericidal concentrations (MBCs) ranged from 0.125 to 1 and 0.25 to 64, 8 to 512 and >512, and 2 to 8 and 8 to 512 microgram/ml, respectively. There were no significant relationships between susceptibilities to the individual components and the susceptibilities to the Q-D combination product. In the time-kill-curves studies, Q-D at a concentration of 6 microgram/ml was at least bacteriostatic against all VREF tested. There was increased activity against more susceptible isolates when the isolates were grouped either by Q-D MBCs or by Q MICs. By multivariate regression analyses, the percent change in the inoculum from that at the baseline was significantly correlated with the Q MIC (R = 0.74; P = 0.008) and the Q-D concentration-to-MBC ratio (R = 0.58; P = 0.02) and was inversely correlated with the Q-D MBC-to-MIC ratio (R = 0.68; P = 0.003). A strong correlation existed between the killing rate and the Q-D concentration-to-MBC ratio (R = 0.99; P < 0.0001). Time to 99.9% killing was best correlated with the Q-D MBC (R = 0.96; P < 0.0001). The postantibiotic effect ranged from 0.2 to 3.2 h and was highly correlated with the Q-D concentration-to-MBC ratio (R = 0.96; P < 0.0001) and was less highly correlated with the Q MIC (R = 0.42; P = 0.04). Further study of these relationships with in vitro or in vivo infection models that simulate Q-D pharmacokinetics should further define the utility of these pharmacodynamic parameters in the prediction of Q-D activity for the treatment of VREF infections in humans.

Omeprazole-induced exfoliative dermatitis

A 41-year-old man being treated for severe esophageal reflux disease developed red, exfoliative scaling on his back, trunk, and legs after taking omeprazole 20 mg twice/day for 3 months. He also had redness and extreme sloughing of the skin on his hands. Even after he discontinued omeprazole and after several courses of topical and systemic steroids, symptoms continued to occur 18 months after treatment, mostly localized to the hands. Exfoliative dermatitis is associated with many drugs, but omeprazole has been implicated only once before in the literature.

The pharmacologic and bacteriologic properties of oxazolidinones, a new class of synthetic antimicrobials

The oxazolidinones are a new synthetic class of antimicrobials structurally unrelated to any agent presently marketed. Data pertaining to these compounds, with respect to their pharmacology, pharmacokinetics, pharmacodynamics, mechanism of action, and bacteriologic activity, focusing on the analogs linezolid (PNU 100766) and eperezolid (PNU 100592), were retrieved by MEDLINE search and review of relevant abstracts presented at recent clinical conferences. Since the drugs are still investigational, we obtained in vitro and animal data as well as available human studies. The oxazolidinones have bacteriostatic activity against a number of important pathogens including methicillin-resistant Staphylococcus aureus, penicillin-resistant Streptococcus pneumoniae, and vancomycin-resistant enterococci. They appear to be efficacious and well tolerated both orally and parenterally. Their role remains to be elucidated by clinical trials.

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.

Comparative in vitro activities and postantibiotic effects of the oxazolidinone compounds eperezolid (PNU-100592) and linezolid (PNU-100766) versus vancomycin against Staphylococcus aureus, coagulase-negative staphylococci, Enterococcus faecalis, and Enterococcus faecium

The activities of the oxazolidinone antibacterial agents eperezolid (PNU-100592) and linezolid (PNU-100766) were compared with that of vancomycin against clinical isolates of methicillin-susceptible and -resistant Staphylococcus aureus (n = 200), coagulase-negative staphylococci (n = 100), and vancomycin-susceptible and -resistant Enterococcus faecalis and Enterococcus faecium (n = 50). Eperezolid and linezolid demonstrated good in vitro inhibitory activity, regardless of methicillin susceptibility for staphylococci (MIC at which 90% of the isolates are inhibited [MIC90] range, 1 to 4 microg/ml) or vancomycin susceptibility for enterococci (MIC90 range, 1 to 4 microg/ml). In time-kill studies, eperezolid and linezolid were bacteriostatic in action. A postantibiotic effect of 0.8+/-0.5 h was demonstrated for both eperezolid and linezolid against S. aureus, S. epidermidis, E. faecalis, and E. faecium.

Trimethoprim/sulfamethoxazole-induced tremor in a patient with AIDS

OBJECTIVE

To report a case of trimethoprim/sulfamethoxazole (TMP/SMX)-induced tremor responsive to a reduction in dosage.

CASE SUMMARY

A 55-year-old white man with AIDS and Pneumocystis carinii pneumonia (PCP) developed a tremor after receiving 5 days of therapy with TMP/SMX 19.4 mg/kg/d (TMP). The tremor resolved completely 3 days after a dosage reduction to TMP/SMX 15.1 mg/kg/d.

DISCUSSION

Central nervous system adverse reactions to TMP/SMX have been reported in both the AIDS and non-AIDS populations. To our knowledge, this is the first reported case of TMP/SMX-induced tremor responsive to a reduction in dosage. Pharmacokinetic and clinical data suggest a concentration-dependent etiology for various adverse effects, including tremor. The mechanism of the tremor is unknown; however, toxic metabolites of SMX and disruptions of biogenic amine neurotransmission by TMP have been hypothesized.

CONCLUSIONS

TMP/SMX remains the drug of first choice for treating PCP, but it is clearly not well tolerated by patients with AIDS. Concentration-dependent toxicities such as tremor may lead to premature discontinuation of proven, effective TMP/SMX therapy. Using the lower end of the recommended dosing range for TMP/SMX (TMP 15 mg/kg/d) may reduce the incidence of these toxicities while still achieving acceptable TMP concentrations and antimicrobial efficacy.

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.