Antibacterial activity of quinupristin/dalfopristin. Rationale for clinical use

Clickable Transformation of Nitriles (RCN) to Oxazolyl Sulfonyl Fluoride Warheads

The protocol for simple, efficient, and mild synthesis of oxazolyl sulfonyl fluorides was developed through Rh₂(OAc)₄-catalyzed annulation of methyl-2-diazo-2-(fluorosulfonyl)acetate (MDF) or its ethyl ester derivative with nitriles. This practical method provides a general and direct route to a unique class of highly functionalized oxazolyl-decorated sulfonyl fluoride warheads with great potential in medicinal chemistry, chemical biology, and drug discovery.

Actinomycete-Derived Polyketides as a Source of Antibiotics and Lead Structures for the Development of New Antimicrobial Drugs

Actinomycetes are remarkable producers of compounds essential for human and veterinary medicine as well as for agriculture. The genomes of those microorganisms possess several sets of genes (biosynthetic gene cluster (BGC)) encoding pathways for the production of the valuable secondary metabolites. A significant proportion of the identified BGCs in actinomycetes encode pathways for the biosynthesis of polyketide compounds, nonribosomal peptides, or hybrid products resulting from the combination of both polyketide synthases (PKSs) and nonribosomal peptide synthetases (NRPSs). The potency of these molecules, in terms of bioactivity, was recognized in the 1940s, and started the "Golden Age" of antimicrobial drug discovery. Since then, several valuable polyketide drugs, such as erythromycin A, tylosin, monensin A, rifamycin, tetracyclines, amphotericin B, and many others were isolated from actinomycetes. This review covers the most relevant actinomycetes-derived polyketide drugs with antimicrobial activity, including anti-fungal agents. We provide an overview of the source of the compounds, structure of the molecules, the biosynthetic principle, bioactivity and mechanisms of action, and the current stage of development. This review emphasizes the importance of actinomycetes-derived antimicrobial polyketides and should serve as a "lexicon", not only to scientists from the Natural Products field, but also to clinicians and others interested in this topic.

Quinupristin/Dalfopristin

Each month, subscribers to The Formulary® Monograph Service receive five to six researched monographs on drugs that are newly released or are in late Phase III trials. The monographs are targeted to your Pharmacy and Therapeutics Committee. Subscribers also receive monthly one-page summary monographs on the agents that are useful for agendas and pharmacy/nursing in-services. A comprehensive target drug utilization evaluation (DUE) is also provided each month. The monographs are published in printed form and on diskettes that allow customization. Subscribers to the The Formulary Monograph Service also receive access to a pharmacy bulletin board called The Formulary Information Exchange (The F.I.X). All topics pertinent to clinical pharmacy are discussed on The F.I.X.

Through the cooperation of The Formulary, Hospital Pharmacy publishes selected reviews in this column. If you would like information about The Formulary Monograph Service or The F.I.X., call The Formulary at 800-322-4349. The February 2000 Formulary monographs are on gatifloxacin, moxifloxacin, levetiracetam, aspirin/extended-release dipyridamole, and aminolevulinic acid HCl. The DUE is on gatifloxacin.

Safety of intravitreal quinupristin/dalfopristin in an animal model

AIM

To determine whether different intravitreal doses of quinupristin/dalfopristin lead to electroretinographic or histological changes in the rabbit retina over one month period after injection.

METHODS

Eighteen New Zealand white rabbits were divided into three treatment groups (groups 1 to 3) and different intravitreal doses of quinupristin/dalfopristin were tested in each group. The right eye was injected with the drug and the left eye received intravitreal injection of 5% dextrose water and served as control eye. The doses delivered to each group were 0.1 mg/0.1 mL, 1 mg/0.1 mL and 10 mg/0.1 mL. Simultaneous, bilateral, dark-adapted electroretinography and clinical images of both eyes were obtained in all groups before injection (baseline) and after 7, 14, 21 and 28d, followed by enucleation for histological examination.

RESULTS

Subjects in the group 1 showed no signs of toxicity in the electroretinogram when compared with groups 2 and 3 (Kruskall-Wallis test, P=0.000). By day 7, no electrical response to light stimuli was recorded in the treated eyes in groups 2 and 3, consistent with severe damage due to retinal toxicity. Light microscopy revealed no significant histopathological changes in the group 1, while rabbits in groups 2 and 3 had signs of granulomatous inflammation in most cases.

CONCLUSION

Intravitreal 0.1 mg/0.1 mL doses of quinupristin/dalfopristin do not lead to electroretinographic or histological signs of retinal toxicity compared with 1 mg/0.1 mL and 10 mg/0.1 mL in this rabbit model.

Endophthalmitis caused by Gram-positive organisms with reduced vancomycin susceptibility: literature review and options for treatment

BACKGROUND

Endophthalmitis caused by Gram-positive organisms with reduced vancomycin susceptibility and/or resistance is an important clinical issue worldwide.

PURPOSE

To review the published literature on endophthalmitis caused by Gram-positive organisms with reduced vancomycin susceptibility and/or vancomycin resistance.

METHODS

The data were analysed from a PubMed search of endophthalmitis cases caused by Gram-positive organisms with reported reduced vancomycin susceptibility and/or vancomycin resistance from 1990 to 2015.

RESULTS

From 18 publications identified, a total of 27 endophthalmitis cases caused by Gram-positive organisms with reduced vancomycin susceptibility and/or vancomycin resistance were identified. The aetiologies of endophthalmitis were exogenous in 19/27 cases (11 post-cataract surgery, 2 post-penetrating keratoplasty, 1 post-glaucoma surgery, 4 post-open globe injury, 1 post-intravitreal injection of ranibizumab), and endogenous in 4/24 cases; no details were available about the four remaining patients. The causative organisms included Enterococcus species (7/27), coagulase-negative staphylococci (4/27), Staphylococcus aureus (4/27), Bacillus species (4/27), Streptococcus species (3/27), Leuconostoc species (3/27), Staphylococcus hominis (1/27), and unidentified Gram-positive cocci (1/27). Visual acuity of 20/400 or better at the final follow-up was recorded in 10/26 patients (38.5%; data were not available for one patient). Treatment options include fluoroquinolones, penicillin, cephalosporins, tetracyclines, and oxazolidinones.

CONCLUSIONS

In the current study, visual acuity outcomes were generally poor. Enterococcus and Staphylococcus species were the most common organisms reported and postoperative endophthalmitis after cataract surgery was the most common clinical setting.

Spectrum and treatment of anaerobic infections

Anaerobes are the most predominant components of the normal human skin and mucous membranes bacterial flora, and are a frequent cause of endogenous bacterial infections. Anaerobic infections can occur in all body locations: the central nervous system, oral cavity, head and neck, chest, abdomen, pelvis, skin, and soft tissues. Treatment of anaerobic infection is complicated by their slow growth in culture, by their polymicrobial nature and by their growing resistance to antimicrobials. Antimicrobial therapy is frequently the only form of therapy needed, whereas in others it is an important adjunct to drainage and surgery. Because anaerobes generally are isolated mixed with aerobes, the antimicrobial chosen should provide for adequate coverage of both. The most effective antimicrobials against anaerobes are: metronidazole, the carbapenems (imipenem, meropenem, doripenem, ertapenem), chloramphenicol, the combinations of a penicillin and a beta-lactamase inhibitors (ampicillin or ticarcillin plus clavulanate, amoxicillin plus sulbactam, piperacillin plus tazobactam), tigecycline, cefoxitin and clindamycin.

Antianaerobic antimicrobials: spectrum and susceptibility testing

Susceptibility testing of anaerobic bacteria recovered from selected cases can influence the choice of antimicrobial therapy. The Clinical and Laboratory Standards Institute (CLSI) has standardized many laboratory procedures, including anaerobic susceptibility testing (AST), and has published documents for AST. The standardization of testing methods by the CLSI allows comparisons of resistance trends among various laboratories. Susceptibility testing should be performed on organisms recovered from sterile body sites, those that are isolated in pure culture, or those that are clinically important and have variable or unique susceptibility patterns. Organisms that should be considered for individual isolate testing include highly virulent pathogens for which susceptibility cannot be predicted, such as Bacteroides, Prevotella, Fusobacterium, and Clostridium spp.; Bilophila wadsworthia; and Sutterella wadsworthensis. This review describes the current methods for AST in research and reference laboratories. These methods include the use of agar dilution, broth microdilution, Etest, and the spiral gradient endpoint system. The antimicrobials potentially effective against anaerobic bacteria include beta-lactams, combinations of beta-lactams and beta-lactamase inhibitors, metronidazole, chloramphenicol, clindamycin, macrolides, tetracyclines, and fluoroquinolones. The spectrum of efficacy, antimicrobial resistance mechanisms, and resistance patterns against these agents are described.

Quinupristin/dalfopristin in Staphylococcus aureus endophthalmitis: a case report

INTRODUCTION

The intravitreal injection of antibiotics remains the mainstay of therapy for postoperative endophthalmitis. Bacterial resistance, however, is still a pitfall in achieving an adequate response to treatment. Quinupristin/dalfopristin might be a feasible therapeutic option in these cases.

CASE PRESENTATION

A 55-year-old Hispanic man had endophthalmitis secondary to Staphylococcus aureus in his right eye and was treated with intravitreal 0.4 mg/0.1 ml quinupristin/dalfopristin injection. Inflammation and pain remission were observed at four days after injection. The final best-corrected visual acuity was 20/40.

CONCLUSION

Although vancomycin remains the first-line intravitreal antibiotic therapy against infectious endophthalmitis caused by Gram-positive bacteria, quinupristin/dalfopristin exhibits similar efficacy and is theoretically more active against vancomycin-resistant strains, with no apparent retinal toxicity.

Antimicrobial resistance in Bacteroides spp.: occurrence and dissemination

Bacteroides spp. organisms, though important human commensals, are also opportunistic pathogens when they escape the colonic milieu. Resistance to multiple antibiotics has been increasing in Bacteroides spp. for decades, and is primarily due to horizontal gene transfer of a plethora of mobile elements. The mechanistic aspects of conjugation in Bacteroides spp. are only now being elucidated at a functional level. There appear to be key differences between Bacteroides spp. and non-Bacteroides spp. conjugation systems that may contribute to promiscuous gene transfer within and from this genus. This review summarizes the mechanisms of action and resistance of antibiotics used to treat Bacteroides spp. infections, and highlights current information on conjugation-based DNA exchange.

Treatment of anaerobic infection

Anaerobic bacteria are the predominant flora in the normal human skin and mucous membranes and are, therefore, a common cause of endogenous infections. Since anaerobic infections are generally polymicrobial, where anaerobes are mixed with aerobic organisms, therapy should provide coverage of both types of pathogens. The isolation of anaerobes requires appropriate methods of collection, transportation and cultivation of specimens. The lack of use of any of these methods can lead to inadequate recovery of anaerobes and inappropriate therapy. Treatment of anaerobic infection is complicated by the slow growth of these organisms and the growing resistance of anaerobic bacteria to antimicrobials. The primary role of antimicrobials is to limit the local and systemic spread of infection. Surgical drainage is of primary importance. This includes debriding of necrotic tissue, draining the pus, improving circulation, alleviating obstruction and increasing tissue oxygenation. The most effective antimicrobials against anaerobic organisms are metronidazole, the carbapenems (imipenem, meropenem and ertapenem), chloramphenicol, the combinations of a penicillin and a beta-lactamase inhibitor (ampicillin or ticarcillin plus clavulanate, amoxicillin plus sulbactam, and piperacillin plus tazobactam), tigecycline and clindamycin.

Methicillin-resistant Staphylococcus aureus: clinical manifestations and antimicrobial therapy

Methicillin-resistant Staphylococcus aureus (MRSA) is a common skin coloniser and less commonly causes infection. MRSA colonisation should be contained by infection control measures and not treated. MRSA infections cause the same spectrum of infection as MSSA infections, i.e., skin/soft tissue infections, bone/joint infections, central IV line infections, and acute bacterial endocarditis (native valve/prosthetic valve). There is a discrepancy between in-vitro sensitivity and in-vivo effectiveness with MRSA. To treat MRSA infections, clinicians should select an MRSA drug with proven in-vivo effectiveness, i.e., daptomycin. Linezolid, quinupristin/dalfopristin, minocycline, or vancomycin, and not rely on in-vitro susceptibility data. For MRSA, doxycycline cannot be substituted for minocycline. Linezolid and minocycline are available for oral administration and both are also effective in treating MRSA CNS infections. Vancomycin is being used less due to side effects, (increasing MICs/resistance, VISA/VRSA), and increased VRE prevalence. The most potent anti-MRSA drug at the present time is daptomycin. Daptomycin is useful when rapid/effective therapy of MRSA bacteraemia/endocarditis is necessary. Daptomycin is also useful to treat persistent MRSA bacteraemias/MRSA treatment failures with other drugs, i.e., vancomycin. There is no difference in virulence between MSSA and MRSA infections if treatment is started early and with an agent that has in-vivo effectiveness.

Designing Antibacterial Compounds through a Topological Substructural Approach

A novel application of TOPological Substructural MOlecular DEsign (TOPS-MODE) was carried out in antibacterial drugs using computer-aided molecular design. Two series of compounds, one containing antibacterial and the other containing non-antibacterial compounds, were processed by a k-means cluster analysis in order to design training and predicting series. All clusters had a p-level < 0.005. Afterward, a linear classification function has been derived toward discrimination between antibacterial and non-antibacterial compounds. The model correctly classifies 94% of active and 86% of inactive compounds in the training series. More specifically, the model showed a global good classification of 91%, i.e., 263 cases out of 289. In predicting series, the model has shown overall predictabilities of 91 and 83% for active and inactive compounds, respectively. Thereby, the model has a global percentage of good classification of 89%. The TOPS-MODE approach, also, similarly compares with respect to one of the most useful models for antimicrobials selection reported to date.

Role of quinupristin/dalfopristin in the treatment of Gram-positive nosocomial infections in haematological or oncological patients

Gram-positive pathogens, primarily Staphylococcus aureus, coagulase-negative staphylococci, viridans group streptococci, and enterococci, are now the predominant causes of infection in neutropenic haematology/oncology patients, but are often resistant to multiple antibiotics. Glycopeptides have been the only alternative antibiotic treatments for multidrug-resistant Gram-positive infections to date. However, glycopeptides are not always effective or well tolerated, and can produce nephrotoxic or ototoxic effects. Quinupristin/dalfopristin is a recently introduced streptogramin antibiotic that is active in vitro against most of the major Gram-positive pathogens causing infection in neutropenic patients. Recent studies of the in vitro susceptibility of clinical isolates of Gram-positive pathogens to quinupristin/dalfopristin are summarized. Pre-clinical and clinical studies of the efficacy and safety of quinupristin/dalfopristin in the treatment of Gram-positive infections are reviewed. Quinupristin/dalfopristin is active in vitro against the vast majority of recent isolates of relevant Gram-positive pathogens, including methicillin-resistant staphylococci, viridans group streptococci, and vancomycin-resistant Enterococcus faecium, but excluding Enterococcus faecalis. Pre-clinical and clinical data indicate the efficacy of quinupristin/dalfopristin in infections caused by these organisms, including bacteraemia and catheter-related infections. Quinupristin/dalfopristin is not associated with nephrotoxicity or ototoxicity. Quinupristin/dalfopristin is a potential alternative to glycopeptides in haematology or oncology patients with multidrug-resistant Gram-positive infections, especially those who are unresponsive to, or intolerant of, glycopeptides.

Dead bugs don't mutate: susceptibility issues in the emergence of bacterial resistance

The global emergence of antibacterial resistance among common and atypical respiratory pathogens in the last decade necessitates the strategic application of antibacterial agents. The use of bactericidal rather than bacteriostatic agents as first-line therapy is recommended because the eradication of microorganisms serves to curtail, although not avoid, the development of bacterial resistance. Bactericidal activity is achieved with specific classes of antimicrobial agents as well as by combination therapy. Newer classes of antibacterial agents, such as the fluoroquinolones and certain members of the macrolide/lincosamine/streptogramin class have increased bactericidal activity compared with traditional agents. More recently, the ketolides (novel, semisynthetic, erythromycin-A derivatives) have demonstrated potent bactericidal activity against key respiratory pathogens, including Streptococcus pneumoniae, Haemophilus influenzae, Chlamydia pneumoniae, and Moraxella catarrhalis. Moreover, the ketolides are associated with a low potential for inducing resistance, making them promising first-line agents for respiratory tract infections.

Osteomyelitis attributable to vancomycin-resistant enterococci

Vancomycin-resistant enterococcus first was described in 1988, and has become a major problem in nosocomial infections. This is a retrospective review of 10 patients, seen at the authors' hospital during a 2-year period, with confirmed vancomycin-resistant enterococcal osteomyelitis: four patients had total joint arthroplasty infections, one patient had an infected tibial nail, three patients had infections associated with external fixators, and two patients had osteomyelitis of the femur. Four of the 10 patients had underlying medical illnesses (diabetes mellitus, systemic lupus erythematosus, human immunodeficiency virus infection); four of the 10 patients were intravenous drug users. Two patients had vancomycin-resistant enterococci on admission, and the other eight patients were admitted to the hospital for a mean of 21.3 days (range, 3-73 days) before vancomycin-resistant enterococci were identified in the bone. Eight of the 10 patients had monomicrobial infections with vancomycin-resistant enterococci. Patients were treated by surgical debridement, removal of hardware, and antibiotics (chloramphenicol in eight patients, quinupristin and dalfopristin (Synercid) in two patients). All patients initially improved with therapy, but one patient had a recurrence of vancomycin-resistant enterococcal osteomyelitis and died of bacteremia. Bone infections with vancomycin-resistant enterococcus still may be uncommon, but with time and selective antibiotic pressures, vancomycin-resistant enterococci may become a more prominent entity in orthopaedic infections.

Successful treatment of vancomycin-resistant enterococcus meningitis with linezolid: Case report and review of the literature

OBJECTIVE

To describe the successful treatment of a case of vancomycin-resistant enterococcus meningitis with linezolid.

DESIGN

Case report and review of the literature.

PATIENTS

The patient is a 35-yr-old man who suffered a cerebellar hemorrhage after embolization of a cerebellar arteriovenous malformation. The patient underwent ventriculostomy drainage and craniectomy. The patient was on broad-spectrum antibiotics for pneumonia including vancomycin. The patient remained febrile and grew vancomycin-resistant Enterococcus faecium from the cerebrospinal fluid.

INTERVENTIONS

The patient was treated with intravenous chloramphenicol without success. On postoperative day 16, the patient was begun on intravenous linezolid.

MAIN RESULTS

The patient received 4 wks of intravenous linezolid with complete eradication of the meningitis.

CONCLUSIONS

Intravenous linezolid appears to be a safe and effective therapy for vancomycin-resistant enterococcus meningitis.

Antimicrobial susceptibility of starter culture bacteria used in Norwegian dairy products

Commercial starter culture bacteria are widely used in the production of dairy products and could represent a potential source for spread of genes encoding resistance to antimicrobial agents. To learn more about the antimicrobial susceptibility of starter culture bacteria used in Norwegian dairy products, a total of 189 isolates of lactic acid bacteria were examined for susceptibility to ampicillin, penicillin G, cephalothin, vancomycin, bacitracin, gentamicin, streptomycin, erythromycin, tetracycline, chloramphenicol, quinupristin/dalfopristin, ciprofloxacin, trimethoprim and sulphadiazine using Etest for MIC determination. Most of the isolates (140) originated from 39 dairy products (yoghurt, sour cream, fermented milk and cheese), while 49 were isolated directly from nine commercial cultures. The bacteria belonged to the genera Lactobacillus, Lactococcus, Leuconostoc and Streptococcus. Only one of the 189 isolates was classified as resistant to an antimicrobial agent included in the study. This isolate, a lactobacillus, was classified as high level resistant to streptomycin. The remaining isolates were not classified as resistant to the antimicrobial agents included other than to those they are known to have a natural reduced susceptibility to. Thus, starter culture bacteria in Norwegian dairy products do not seem to represent a source for spread of genes encoding resistance to antimicrobial agents.

Antibiotic resistance rates and macrolide resistance phenotypes of viridans group streptococci from the oropharynx of healthy Greek children

A total of 200 isolates of viridans group streptococci isolated from the oropharynx of healthy Greek children were studied. Vancomycin, rifampicin, fluoroquinolones and dalfopristin/quinupristin were active against all tested isolates. High level resistance to gentamicin was not seen. Intermediate and high-level penicillin resistance was present in 28.5 and 14.5% isolates, respectively, with 41.3% of the latter group, being also resistant to cefotaxime. Resistance rates to other antimicrobials were as follows - erythromycin 38.5%, clarithromycin 33.5%, clindamycin 7.5% and tetracycline 23%. Penicillin resistance occurred more frequently in Streptococcus mitis isolates, while macrolide resistance was more frequent in S. oralis. MLSB resistance phenotype M was dominant (74%) among erythromycin resistant isolates, with phenotypes IR and CR being represented by 6 and 20% of isolates, respectively.

Systemic antibiotic agents

Understanding the breadth of systemic antimicrobial agents available for use by the dermatologist and their associated side-effect profiles and drug interactions allows the clinician to offer patients optimal care in the management of cutaneous infectious disease.

Antienterococcal antibiotics

The treatment of severe enterococcal infections based on the currently available antibacterial agents is difficult. The help of the microbiology laboratory for determining MICs, MBCs, and most effective synergistic combinations is crucial. There is a need for good prospective multicenter clinical trials to improve the prognosis of such infections by defining therapeutic strategies better. Such a requirement is highly suitable for the treatment of infections caused by enterococci exhibiting acquired resistance mechanisms to the available agents. The current clinical development of new compounds looks promising in these persistently life-threatening infections mostly occurring in deficient hosts.

Quinupristin-dalfopristin combined with beta-lactams for treatment of experimental endocarditis due to Staphylococcus aureus constitutively resistant to macrolide-lincosamide-streptogramin B antibiotics

Quinupristin-dalfopristin (Q-D) is an injectable streptogramin active against most gram-positive pathogens, including methicillin-resistant Staphylococcus aureus (MRSA). In experimental endocarditis, however, Q-D was less efficacious against MRSA isolates constitutively resistant to macrolide-lincosamide-streptogram B (C-MLS(B)) than against MLS(B)-susceptible isolates. To circumvent this problem, we used the checkerboard method to screen drug combinations that would increase the efficacy of Q-D against such bacteria. beta-Lactams consistently exhibited additive or synergistic activity with Q-D. Glycopeptides, quinolones, and aminoglycosides were indifferent. No drugs were antagonistic. The positive Q-D-beta-lactam interaction was independent of MLS(B) or beta-lactam resistance. Moreover, addition of Q-D at one-fourth the MIC to flucloxacillin-containing plates decreased the flucloxacillin MIC for MRSA from 500 to 1,000 mg/liter to 30 to 60 mg/liter. Yet, Q-D-beta-lactam combinations were not synergistic in bactericidal tests. Rats with aortic vegetations were infected with two C-MLS(B)-resistant MRSA isolates (isolates AW7 and P8) and were treated for 3 or 5 days with drug dosages simulating the following treatments in humans: (i) Q-D at 7 mg/kg two times a day (b.i.d.) (a relatively low dosage purposely used to help detect positive drug interactions), (ii) cefamandole at constant levels in serum of 30 mg/liter, (iii) cefepime at 2 g b.i.d., (iv) Q-D combined with either cefamandole or cefepime. Any of the drugs used alone resulted in treatment failure. In contrast, Q-D plus either cefamandole or cefepime significantly decreased valve infection compared to the levels of infection for both untreated controls and those that received monotherapy (P < 0.05). Importantly, Q-D prevented the growth of highly beta-lactam-resistant MRSA in vivo. The mechanism of this beneficial drug interaction is unknown. However, Q-D-beta-lactam combinations might be useful for the treatment of complicated infections caused by multiple organisms, including MRSA.

In vitro activity of quinupristin/dalfopristin against selected bacterial pathogens isolated in Italy

OBJECTIVE: To evaluate the activity of quinupristin/dalfopristin, a new injectable streptogramin, against 732 clinical strains recently isolated in Italy. METHODS: Susceptibility tests were performed according to NCCLS-guided MIC methodology. Pathogens included in the evaluation included 108 Staphylococcus aureus isolates, 124 coagulase-negative staphylococcal isolates, 158 Streptococcus pyogenes isolates, 30 Streptococcus agalactiae isolates, 30 b-hemolytic streptococcal isolates, 18 Streptococcus sanguis isolates, 80 Streptococcus pneumoniae isolates, 69 Enterococcal isolates, 40 Haemophilus influenzae isolates, 30 Moraxella catarrhalis isolates and, finally, 30 Gram-positive and 25 Gram-negative anaerobes. RESULTS: Quinupristin/dalfopristin inhibited Staphylococcus aureus and other Staphylococcus spp., irrespective of their oxacillin or erythromycin resistance phenotypes. Similarly, streptococci were fully inhibited by quinupristin/dalfopristin. Enterococcus faecalis was not included in the spectrum of this streptogramin, while isolates of Enterococcus faecium were inhibited by the new compound. Respiratory pathogens such as H. influenzae and M. catarrhalis were inhibited by quinupristin/dalfopristin as well as all Gram-negative anaerobes tested. CONCLUSIONS: These findings suggest a putative role for quinupristin/dalfopristin in the empirical treatment of severe nosocomial and community-acquired infections caused by pathogens often displaying resistance to multiple antibiotics. This drug may provide an alternative to glycopeptide compounds.

Pharmacokinetics of quinupristin-dalfopristin in continuous ambulatory peritoneal dialysis patients

Quinupristin-dalfopristin may be useful for treatment of organisms causing peritoneal dialysis-related peritonitis, including methicillin-resistant coagulase-negative staphylococci, methicillin-resistant Staphylococcus aureus, and vancomycin-resistant enterococci. The pharmacokinetic profiles of single intravenous doses of this combination streptogramin antibiotic of 7.5 mg/kg of body weight were characterized for eight noninfected patients receiving continuous ambulatory peritoneal dialysis. Comparison was made to pharmacokinetic profiles determined for eight healthy volunteers matched by age, sex, and race. Drug was measured in dialysate up to 6 h following the dose. Plasma and dialysate were assayed for parent compounds and metabolites. Mean pharmacokinetic parameters were compared between groups. No statistically significant differences were observed between groups for maximal concentrations in plasma, times to maximal concentration, areas under the curve, distribution volumes, rates of total body clearance, or half-lives in plasma for quinupristin and dalfopristin. No statistically significant differences were observed in maximal concentrations in plasma, times to maximal concentration, areas under the curve, or half-lives for cysteine, the glutathione conjugates of quinupristin, or the pristinamycin IIA metabolite of dalfopristin. The measurements in dialysate of the parent and most metabolites were below the expected MICs. Dialysis clearance was insignificant. Quinupristin-dalfopristin was well tolerated in both groups, causing only mild adverse events that resolved prior to discharge from the study. The disposition of quinupristin, dalfopristin, or their primary metabolites following a single dose was unaltered in patients receiving peritoneal dialysis. Intravenous dosing of this antibiotic combination is unlikely to be adequate for the treatment of peritonitis associated with peritoneal dialysis.

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.

In vitro antimicrobial activity and MIC quality control guidelines of RPR 106972 (RPR 112808/RPR106950): a novel orally administered streptogramin combination. The Quality Control Study Group

RPR 106972 is a novel oral streptogramin combination with reported therapeutic potency against Gram-positive and certain respiratory tract pathogens. MICs for RPR 106972, quinupristin/dalfopristin, and seven comparison drugs were determined by the reference methods against 337 strains selected to define spectrum and potency. RPR 106972 demonstrated antimicrobial activity against oxacillin-susceptible and -resistant Staphylococcus aureus (MIC ranges of 0.12 to 2 micrograms/ml and 0.5 to 2 micrograms/ml, respectively), and coagulase-negative staphylococci were also inhibited by RPR 106972 (MIC90, < or = 0.5 microgram/ml) and quinupristin/dalfopristin (MIC90, < or = 0.25 microgram/ml). Against all streptococcal strains tested (including penicillin-resistant pneumococcus), RPR 106972 was highly active with MIC results at < or = 1 microgram/ml. RPR 106972 inhibited Corynebacterium jeikeium (MIC90, 0.5 microgram/ml). Moraxella catarrhalis (MIC90, 0.25 microgram/ml), and some Haemophilus influenzae (MIC50, 2 micrograms/ml). RPR 106972 and quinupristin/dalfopristin demonstrated little activity against Enterococcus faecalis (MIC90s, 4 to 32 micrograms/ml) as compared to Enterococcus faecium (MIC90s, 0.5 to 1 microgram/ml) and other Enterococcus ssp. (MIC90s, 1 microgram/ml). Studies to establish MIC quality-control guidelines indicated the following ranges: for E. faecalis ATCC 29212, 0.5 to 4 micrograms/ml; for S. aureus ATCC 29213, 0.25 to 1 microgram/ml; and for Streptococcus pneumoniae ATCC 49619, 0.06 to 0.5 microgram/ml. The results of this study indicate that the in vitro activity of RPR 106972 against Gram-positive bacteria and selected Gram-negative respiratory organisms is promising and warrants additional studies of pharmacokinetics, and in vivo infection model dynamics.