Comparative in-vitro activity of RP 59500 against clinical bacterial isolates

Role of macrolide therapy in chronic obstructive pulmonary disease

Chronic obstructive pulmonary disease (COPD) is a leading cause of death and disability worldwide. The Global Burden of Disease study has concluded that COPD will become the third leading cause of death worldwide by 2020, and will increase its ranking of disability-adjusted life years lost from 12th to 5th. Acute exacerbations of COPD (AECOPD) are associated with impaired quality of life and pulmonary function. More frequent or severe AECOPDs have been associated with especially markedly impaired quality of life and a greater longitudinal loss of pulmonary function. COPD and AECOPDs are characterized by an augmented inflammatory response. Macrolide antibiotics are macrocyclical lactones that provide adequate coverage for the most frequently identified pathogens in AECOPD and have been generally included in published guidelines for AECOPD management. In addition, they exert broad-ranging, immunomodulatory effects both in vitro and in vivo, as well as diverse actions that suppress microbial virulence factors. Macrolide antibiotics have been used to successfully treat a number of chronic, inflammatory lung disorders including diffuse panbronchiolitis, asthma, noncystic fibrosis associated bronchiectasis, and cystic fibrosis. Data in COPD patients have been limited and contradictory but the majority hint to a potential clinical and biological effect. Additional, prospective, controlled data are required to define any potential treatment effect, the nature of this effect, and the role of bronchiectasis, baseline colonization, and other cormorbidities.

Combining Quinupristin/Dalfopristin with Other Agents for Resistant Infections

OBJECTIVE

To review the resistance mechanisms of Enterococcus and Staphylococcus spp. and summarize quinupristin/dalfopristin's (QD's) effects on these resistant organisms when combined with other antibiotics via review of the literature and unpublished data.

DATA SOURCES

Data were identified by a PubMed search (1996—May 2003) using the search terms quinupristin/dalfopristin, synergy, in vitro, in vivo, vancomycin-resistant Enterococcus faecium (VREF), methicillin-resistant Staphylococcus aureus (MRSA), and individual antibiotic names. Bibliographies of the resultant PubMed searches were reviewed and included if applicable.

STUDY SELECTION AND DATA EXTRACTION

All studies reviewed were analyzed; specific drug data were included only if clinically pertinent. In vitro data from studies with adequate design were discussed, whereas all case reports and clinical trials were utilized.

DATA SYNTHESIS

In the treatment of VREF, available information seems conflicting, although some clear differences have become apparent. QD—ampicillin and QD—doxycycline combinations have demonstrated beneficial activity, usually displaying synergistic or additive effects even in macrolide-, lincosamine-, and streptogramin-resistant (MLSB) isolates. Vancomycin and chloramphenicol have shown some efficacy, but antagonistic or null results also have been observed. Regarding MRSA, results from many studies of QD combinations have been ambiguous. More common combinations displayed synergy or additive effects against MRSA, but only QD—rifampin showed consistent beneficial activity against MRSA and MLSB isolates. Most other combinations displayed antagonism when tested in vitro.

CONCLUSIONS

Data supporting the use of various QD—antibiotic combinations against VREF and MRSA are increasing, but further in vitro and in vivo data are needed to confirm the findings.

Daptomycin

Daptomycin, the first in a class of agents known as lipopeptides, is a novel antimicrobial agent used for the treatment of gram-positive infections. The compound has a distinctive mechanism of action that exerts its bactericidal activity by disrupting plasma membrane function without penetrating into the cytoplasm. The agent has received much interest because of its activity against multidrug-resistant, gram-positive bacteria such as methicillin-resistant Staphylococcus aureus, vancomycin-resistant enterococci, and glycopeptide-intermediate and -resistant S. aureus. Daptomycin demonstrates concentration-dependent killing and is eliminated primarily by glomerular filtration. It was approved in September 2003 for the treatment of complicated skin and soft tissue infections. It has a safety profile similar to other agents commonly administered to treat gram-positive infections. Daptomycin is a welcome addition to the antimicrobial armamentarium for the treatment of bacterial infections. Further clinical experience with this compound will help define its role in the treatment of resistant gram-positive organisms.

Plasmid-encoded metallo-beta-lactamase (IMP-6) conferring resistance to carbapenems, especially meropenem

In 1996, Serratia marcescens KU3838 was isolated from the urine of a patient with a urinary tract infection at a hospital in northern Japan and was found to contain the plasmid pKU501. Previously, we determined that pKU501 carries bla(IMP) and the genes for TEM-1-type beta-lactamases as well as producing both types of beta-lactamases (H. Yano, A. Kuga, K. Irinoda, R. Okamoto, T. Kobayashi, and M. Inoue, J. Antibiot. 52:1135-1139, 1999). pKU502 is a recombinant plasmid that contains a 1.5-kb DNA fragment, including the metallo-beta-lactamase gene, and is obtained by PCR amplification of pKU501. The sequence of the metallo-beta-lactamase gene in pKU502 was determined and revealed that this metallo-beta-lactamase gene differed from the gene encoding IMP-1 by one point mutation, leading to one amino acid substitution: 640-A in the base sequence of the IMP-1 gene was replaced by G, and Ser-196 was replaced by Gly in the mature enzyme. This enzyme was designated IMP-6. The strains that produced IMP-6 were resistant to carbapenems. The MICs of panipenem and especially meropenem were higher than the MIC of imipenem for these strains. The k(cat)/K(m) value of IMP-6 was about sevenfold higher against meropenem than against imipenem, although the MIC of meropenem for KU1917, which produced IMP-1, was lower than that of imipenem, and the MIC of panipenem was equal to that of imipenem. These results support the hypothesis that IMP-6 has extended substrate profiles against carbapenems. However, the activity of IMP-6 was very low against penicillin G and piperacillin. These results suggest that IMP-6 acquired high activity against carbapenems, especially meropenem, via the point mutation but in the process lost activity against penicillins. Although IMP-6 has reduced activity against penicillins due to this point mutation, pKU501 confers resistance to a variety of antimicrobial agents because it also produces TEM-1-type enzyme.

Quinupristin-dalfopristin: an overview

Synercid (RP 59500), the first injectable streptogramin antibiotic, is composed of two semisynthetic pristinamycin derivatives, quinupristin and dalfopristin. Individually, each component has bacteriostatic activity against staphylococci and streptococci, but together, the agents exhibit synergy, leading to bactericidal activity. The combination drug, however, is bacteriostatic against Enterococcus faecium and has poor activity against Enterococcus faecalis. Despite a short half-life, an extended postantibiotic effect allows the agent to be dosed every 8-12 hours. Both drugs are largely hepatically metabolized and excreted in bile. Although not metabolized by cytochrome P450 3A4, quinupristin-dalfopristin can inhibit agents that are metabolized through this pathway. Dosage adjustments may be necessary in patients with hepatic dysfunction. Alterations in renal function have minimal effects on the agent's pharmacokinetics. Adverse events include arthralgia, myalgias, and infusion-related pain. Based on available data, quinupristin-dalfopristin appears to have a role in treating severely ill patients with infections due to multiresistant gram-positive pathogens.

Pulsed-field gel electrophoresis analysis of nasopharyngeal flora in children attending a day care center

To investigate how bacterial pathogens spread from child to child in a day care center, we monitored six children, two boys and four girls, born between August 1995 and November 1997, attending a day care center and analyzed nasopharyngeal samples from them using pulsed-field gel electrophoresis (PFGE). We obtained nasopharyngeal cultures from all of the affected children and almost all of the unaffected children between September 1998 and March 1999 after some children presented simultaneously with purulent rhinorrhea. Moreover, when a child was found to have acute otitis media, nasopharyngeal secretions from the child were independently cultured during treatment. During this period, 28 isolates of Moraxella catarrhalis, 13 of Streptococcus pneumoniae, and 4 of Haemophilus influenzae were recovered. PFGE gave 8 patterns for M. catarrhalis, 10 for S. pneumoniae, and 1 for H. influenzae. PFGE patterns demonstrated spread of M. catarrhalis between children. However, each occurrence of clusters of infection with M. catarrhalis lasted 2 to 6 weeks, with a change in PFGE pattern between occurrences of clusters. The M. catarrhalis strain infecting each child also changed. Similarly, the S. pneumoniae strain in each child also changed. In contrast, infection with H. influenzae persisted for about 3 months in an affected child.

Quinupristin/dalfopristin: a review of its use in the management of serious gram-positive infections

Quinupristin/dalfopristin is the first parenteral streptogramin antibacterial agent, and is a 30:70 (w/w) ratio of 2 semisynthetic pristinamycin derivatives. The combination has inhibitory activity against a broad range of gram-positive bacteria including methicillin-resistant staphylococci, vancomycin-resistant Enterococcus faecium (VREF), drug-resistant Streptococcus pneumoniae, other streptococci, Clostridium perfringens and Peptostreptococcus spp. The combination also has good activity against selected gram-negative respiratory tract pathogens including Moraxella catarrhalis, Legioniella pneumophila and Mycoplasma pneumoniae. Quinupristin/dalfopristin has poor activity against E. faecalis. The combination is bactericidal against staphylococci and streptococci, although constitutive erythromycin resistance can affect its activity. As for many other agents, quinupristin/dalfopristin is generally bacteriostatic against E. faecium. In patients with methicillin-resistant S. aureus (MRSA) or VREF infections participating in prospective emergency-use trials, quinupristin/dalfopristin 7.5 mg/kg every 8 or 12 hours achieved clinical or bacteriological success in > or =64% of patients. Emergence of resistance to quinupristin/dalfopristin was uncommon (4% of patients) in those with VREF infections. Quinupristin/dalfopristin 7.5 mg/kg 8- or 12-hourly also achieved similar clinical success rates to comparator agents in patients with presumed gram-positive complicated skin and skin structure infections or nosocomial pneumonia (administered in combination with aztreoman) in 3 large multicentre randomised trials. Systemic adverse events associated with quinupristin/dalfopristin include gastrointestinal events (nausea, vomiting and diarrhoea), rash and pruritus. Myalgias and arthralgias also occur at an overall incidence of 1.3%, although higher rates (2.5 to 31%) have been reported in patients with multiple comorbidities. Venous events are common if the drug is administered via a peripheral line; however, several management options (e.g. use of central venous access, increased infusion volume) may help to minimise their occurrence. Hyperbilirubinaemia has been documented in 3.1% of quinupristin/dalfopristin recipients versus 1.3% of recipients of comparator agents. Quinupristin/dalfopristin inhibits cytochrome P450 3A4 and therefore has the potential to increase the plasma concentrations of substrates of this enzyme.

CONCLUSIONS

Quinupristin/dalfopristin, the first parenteral streptogramin, offers a unique spectrum of activity against multidrug-resistant gram-positive bacteria. In serious gram-positive infections for which there are other treatment options available, the spectrum of activity and efficacy of quinupristin/ dalfopristin should be weighed against its tolerability and drug interaction profile. However, in VREF or unresponsive MRSA infections, where few proven treatment options exist, quinupristin/dalfopristin should be considered as a treatment of choice for these seriously ill patients.

Antimicrobial activity of quinupristin/dalfopristin, a new injectable streptogramin with a wide Gram-positive spectrum

Quinupristin/dalfopristin (Synercid) is a new injectable streptogramin antibiotic proposed for the treatment of severe antimicrobial infections, that has been shown to be active against Gram-positive, multi-resistant cocci. We compared the in vitro activity of quinupristin/dalfopristin with that of amoxycillin, ampicillin, penicillin, cefixime, ceftriaxone, clindamycin, erythromycin, imipenem, meropenem, oxacillin, piperacillin/tazobactam, teicoplanin and vancomycin. The susceptibility of 37 Staphylococcus aureus (14 MS, 23 MR), 26 Staphylococcus epidermidis (16 MS, 10 MR), 20 Streptococcus pneumoniae, 33 Group A Streptococcus pyogenes, 15 Streptococcus agalactiae, 10 Enterococcus faecalis (1 vancomycin-resistant), 15 Enterococcus faecium (9 van A) was evaluated. Quinupristin/dalfopristin was active against all Gram-positive species tested, including met-R S. aureus (MIC < or = 2 mg/l), met-R S. epidermidis (MIC < or = 2 mg/l), S. pneumoniae (MIC < or = 1 mg/l), ery-R and ery-S streptococci (MIC < or = 1 mg/l). The strains of E. faecalis were generally less susceptible. Time-kill studies confirmed that quinupristin/dalfopristin at 4 x MIC concentration showed a complete bactericidal effect (3 log reduction) in about 4 6 h against all strains tested. A post-antibiotic effect (PAE) of 3.9-5.2 h was observed at 4 x MIC concentration of quinupristin/dalfopristin against staphylococci. A prolonged PAE was obtained for S. pneumoniae (8 h), S. pyogenes (9 h) and S. agalactiae (7 h), while the shortest PAE was seen for E. faecalis and E. faecium (about 4 h).

In vitro activity of quinupristin/dalfopristin and newer quinolones combined with gentamicin against resistant isolates of Enterococcus faecalis and Enterococcus faecium

In a study designed to obtain data on compounds active against enterococci, the minimum inhibitory concentrations (MICs) of quinupristin/dalfopristin (RP 59500) and the novel quinolones DU-6859a, trovafloxacin, levofloxacin, and sparfloxacin were determined for 122 Enterococcus faecalis and seven Enterococcus faecium isolates. In addition, 15 Enterococcus faecalis isolates resistant to gentamicin, DU-6859a, and trovafloxacin were exposed over time to combinations of DU-6859a plus gentamicin and trovafloxacin plus gentamicin. DU-6859a and trovafloxacin were found to be the most active compounds against Enterococcus faecalis and DU-6859a and RP 59500 against Enterococcus faecium. Synergy between either DU-6859a or trovafloxacin and gentamicin was observed with 27 to 35% of the isolates. It is concluded that DU-6859a and trovafloxacin are very potent against enterococci, especially when combined with gentamicin.

In vitro activity of LY333328, an investigational glycopeptide antibiotic, against enterococci and staphylococci

The in vitro activities of LY333328 were compared with those of vancomycin, teicoplanin, and quinupristin-dalfopristin (Synercid) against 219 strains of enterococci and staphylococci, including vancomycin-resistant enterococci and methicillin-resistant Staphylococcus aureus. MICs and MBCs were determined by a microtiter dilution protocol. LY333328 demonstrated superior activity against vancomycin-resistant enterococci and was the only antibiotic which was bactericidal. Its potency was comparable or superior to those of other antibiotics tested against methicillin-resistant staphylococci.

Quinupristin-dalfopristin

Quinupristin-dalfopristin (RP 59500) is an injectable streptogramin antibiotic. It possesses a wide spectrum of activity against Gram-positive bacteria including methicillin-resistant staphylococci, glycopeptide-resistant. Enterococcus faecium and penicillin-resistant pneumococci. Quinupristin-dalfopristin has activity against some anaerobes and selected Gram-negative pathogens. Quinupristin-dalfopristin, by way synergism of between its 2 components, is unaffected by most forms of bacterial resistance. Rare forms of macrolide-lincosamide-streptogramin group B resistance may affect its activity; however, at present the incidence of strains with this type of resistance remains low. Quinupristin-dalfopristin is bactericidal against streptococci and staphylococci but has weak or no bactericidal activity against enterococci. In a compassionate use programme, 67% of 95 evaluable patients with vancomycin-resistant Gram-positive infections or intolerant of vancomycin showed improvement with eradication of infection.

In-vitro activity of RP 59500, a new semisynthetic injectable pristinamycin against staphylococci

We compared the in vitro activity of RP 59500, a new streptogramin, with that of vancomycin and ciprofloxacin against 130 strains of S. aureus and 117 strains of coagulase-negative staphylococci, using the agar dilution method. The antistaphylococcal activity of RP 59500 was similar to that of vancomycin. All staphylococcal strains were inhibited by < or = 2 micrograms/mL, including 61 methicillin-resistant S. aureus, 28 methicillin-resistant S. epidermidis and 23 methicillin-resistant S. haemolyticus strains. In contrast to ciprofloxacin, the in vitro activity of RP 59500 as well as of vancomycin remained almost unchanged, irrespective of the resistance phenotype for methicillin.

Antibacterial activity of quinupristin/dalfopristin. Rationale for clinical use

Most Gram-positive organisms are highly susceptible to the streptogramin, quinupristin/dalfopristin (RP 59500; Synercid). Minimum inhibitory concentrations for 90% of isolates (MIC90) were < or = 1 mg/L for Staphylococcus aureus, S. epidermidis, S. haemolyticus, Streptococcus pneumoniae, S. pyogenes and Listeria monocytogenes. Importantly, quinupristin/dalfopristin shows similar activity against methicillin-susceptible and -resistant strains of S. aureus, and streptococci with benzylpenicillin (penicillin G)- or erythromycin-acquired resistance. Enterococci have varying susceptibility to quinupristin /dalfopristin, although most isolates tested are susceptible to the drug, including vancomycin-resistant and multiresistant Enterococcus faecium. E. faecalis are generally the least susceptible. Among the Gram-negative respiratory pathogens Moraxella catarrhalis is susceptible and Haemophilus influenzae is moderately susceptible to quinupristin/ dalfopristin; however, Enterobacteriaceae, Pseudomonas aeruginosa and Acinetobacter spp. are resistant. The drug is active against anaerobic organisms tested, including Clostridium perfringens, Lactobacillus spp., Bacteroides fragilis and Peptostreptococcus. Synergy has been demonstrated in vancomycin-resistant and multiresistant E. faecium, and methicillin-sensitive and -resistant S. aureus with the combination of vancomycin and quinupristin/ dalfopristin. Quinupristin/dalfopristin shows antibacterial activity in vivo in animal models of infection, including methicillin-sensitive and -resistant S. aureus infection in rabbits, S. aureus and S. pneumoniae in mice, and erythromycin-sensitive and -resistant viridans group streptococci infections in rats. The drug is rapidly bactericidal against Gram-positive organisms (with the exception of enterococci) at concentrations similar to or within 4-fold of the MIC, and it has a long postantibiotic effect both in vitro and in vivo.

Quinupristin/dalfopristin (RP 59500): a new streptogramin antibiotic

OBJECTIVE

To review the current knowledge on RP 59500 (quinupristin/dalfopristin, Synercid), a new streptogramin antibiotic, with respect to its pharmacology, pharmacokinetics, pharmacodynamics, mechanism of resistance, and in vitro inhibitory and bactericidal activity.

DATA SOURCES

A MEDLINE search using keywords RP 59500, pristinamycin, virginiamycin, and streptogramin was performed. Relevant abstracts presented at recent scientific conferences also were consulted.

STUDY SELECTION

Because RP 59500 is a relatively new investigational agent, relevant in vitro and animal studies were selected. All available human studies were included as well.

DATA EXTRACTION

Data from in vitro and in vivo studies were included, with particular emphasis on human studies.

DATA SYNTHESIS

RP 59500 is a new injectable streptogramin antibiotic consisting of a mixture o 2 synergistic pristinamycin compounds. RP 59500 possesses in vitro inhibitory and bactericidal activity against most isolates of gram-positive organisms including vancomycin-resistant Enterococcus faecium, selected gram-negative bacteria, and most anaerobic organisms. Based on preliminary data, the drug appears to be metabolized rapidly and extensively while exhibiting a significant postantibiotic effect. Data from ongoing clinical trials suggests that RP 59500 is well-tolerated except for mild injection site irritations. However, before the role of RP 59500 within the vast armamentarium of antimicrobials can be elucidated, additional studies need to be conducted to document its clinical efficacy.

CONCLUSIONS

Based on in vitro susceptibility testing, in vivo studies, and preliminary clinical data, RP 59500 may be an alternative to the glycopeptides, especially for inherently resistant organisms. Further studies are needed to confirm this agent's in vitro activity and to establish its clinical efficacy.

Treatment of experimental endocarditis due to erythromycin-susceptible or -resistant methicillin-resistant Staphylococcus aureus with RP 59500

RP 59500 is a new injectable streptogramin composed of two synergistic components (quinupristin and dalfopristin) which are active against erythromycin-susceptible and -resistant gram-positive pathogens. The present experiments compared the therapeutic efficacy of RP 59500 with that of vancomycin against experimental endocarditis due to either of two erythromycin-susceptible or two constitutively erythromycin-resistant isolates of methicillin-resistant Staphylococcus aureus. RP 59500 had low MICs for the four test organisms as well as for 24 additional isolates (the MIC at which 90% of the isolates were inhibited was < 1 mg/liter) which were mostly inducibly (47%) or constitutively (39%) erythromycin resistant. Aortic endocarditis in rats was produced with catheter-induced vegetations. Three-day therapy was initiated 12 h after infection, and the drugs were delivered via a computerized pump, which permitted the mimicking of the drug kinetics produced in human serum by twice-daily intravenous injections of 7 mg of RP 59500 per kg of body weight or 1 g of vancomycin. Both antibiotics reduced vegetation bacterial titers to below detection levels in ca. 70% of animals infected with the erythromycin-susceptible isolates (P < 0.05 compared with titers in controls). Vancomycin was also effective against the constitutively resistant strains, but RP 59500 failed against these isolates. Further experiments proved that RP 59500 failures were related to the very short life span of dalfopristin in serum (< or = 2 h, compared with > or = 6 h for quinupristin), since successful treatment was restored by artificially prolonging the dalfopristin levels for 6 h. Thus, RP 59500 is a promising alternative to vancomycin against methicillin-resistant S. aureus infections, provided that pharmacokinetic parameters are adjusted to afford prolonged levels of both of its constituents in serum. This observation is also relevant to humans, in whom the life span of dalfopristin in serum is also shorter than that of quinupristin.

Cefotaxime in the treatment of staphylococcal infections. Comparison of in vitro and in vivo studies

Staphylococcus aureus strains are well-established pathogens that may cause mild to serious life-threatening disease. Coagulase-negative staphylococci, particularly Staphylococcus epidermidis, also have a pathogenic role in humans and cause infections primarily associated with prosthetic devices and indwelling catheters, whereas Staphylococcus saprophyticus usually causes urinary tract infections. Cefotaxime is a "third-generation" cephalosporin that is stable to the staphylococcal beta-lactamases. In vitro studies over the last 15 years have shown that this parenteral cephalosporin has remained highly active (MIC90 ranges of < or = 2-8 micrograms/ml) against oxacillin-susceptible staphylococci. Cefotaxime therapy of staphylococcal infections has resulted in clinical cure/improvement rates ranging from 78%-100% and bacteriologic eradication rates ranging from 85%-100% in a wide variety of infections. Contrary to contemporary dogma, this "third-generation" cephalosporin appears to be efficacious against staphylococcal infections from a review of 15 years of clinical experience.

In vitro activity of RP 59500 (quinupristin/dalfopristin) against antibiotic-resistant strains of Streptococcus pneumoniae and enterococci

The activity of RP 59500 (quinupristin/dalfopristin) was evaluated in vitro against antibiotic-resistant strains of Streptococcus pneumoniae (N = 15) and Enterococcus spp. (N = 43). By broth dilution MIC tests RP 59500 was highly active against penicillin-resistant S. pneumoniae and vancomycin-resistant Enterococcus faecium, but showed poor activity against E. faecalis. In time-kill studies the drug was rapidly bactericidal against S. pneumoniae but failed to kill most enterococci, even in the presence of gentamicin or human serum.