Treatment of hospitalized patients with complicated gram-positive skin and skin structure infections: two randomized, multicentre studies of quinupristin/dalfopristin versus cefazolin, oxacillin or vancomycin. Synercid Skin and Skin Structure Infection Group

Successful administration of quinupristin/dalfopristin in the outpatient setting

Intravenous administration of quinupristin/dalfopristin outside the hospital setting has not been reported previously. We describe 37 outpatients receiving quinupristin/dalfopristin iv for infections including osteomyelitis, bacteraemia, abscesses and cellulitis. The most frequent aetiological pathogens found were Enterococcus faecium, Staphylococcus aureus and coagulase-negative staphylococci. Patients received an average of 9 days therapy as inpatients and 22 days as outpatients. Quinupristin/dalfopristin was administered using various access devices, most commonly peripherally inserted central catheters and tunnelled central catheters. The bacteriological and clinical success rates were both 89.2%. Five patients were readmitted to hospital; one patient developed catheter-related bacteraemia. The most frequently reported non-venous adverse events were nausea (18.9% of patients), myalgia (18.9%) and arthralgia (13.5%). Sixteen patients experienced venous access-related events, most commonly infusion pain, oedema and phlebitis. In this group of patients, for those who had difficult-to-treat infections, intravenous quinupristin/dalfopristin therapy was generally effective and safe outside the hospital setting.

Linezolid for the treatment of community-acquired pneumonia in hospitalized children. Linezolid Pediatric Pneumonia Study Group

OBJECTIVE

To determine the safety, tolerance, pharmacokinetics and efficacy of linezolid, a new oxazolidinone antibiotic in the treatment of community-acquired pneumonia in hospitalized children.

DESIGN

A Phase II, open label multicenter study of intravenous linezolid followed by oral linezolid suspension, both at a dose of 10 mg/kg every 12 h. Efficacy was assessed at 7 to 14 days after the last dose of linezolid.

PATIENTS

Children 12 months to 17 years old with community-acquired pneumonia admitted to the hospital of 14 participating centers.

RESULTS

From July 21, 1998, through May 14, 1999, 79 children were enrolled and 78 received linezolid. Sixty-six children completed treatment and follow-up and were evaluable for clinical outcome. The median age of the evaluable patients was 3 years (range, 1 to 12 years); 47 were 2 to 6 years old. Pathogens were isolated from blood or pleural fluid cultures in 8 children: Streptococcus pneumoniae, 6 (2 penicillin-resistant); Group A Streptococcus, 1; methicillin-resistant Staphylococcus aureus, 1. Chest tubes were placed in 9 patients. The mean total duration of intravenous and oral administration was 12.2 +/- 6.2 days (range, 6 to 41 days). The mean peak and trough plasma concentrations of linezolid were 9.5 +/- 4.8 and 0.8 +/- 1.2 microg/ml, respectively. At the follow-up visit 7 to 14 days after the last dose of linezolid, 61 patients (92.4%) were considered cured including all the patients with proven pneumococcal pneumonia, one failed (methicillin-resistant Staphylococcus aureus) and 4 were considered indeterminate. The most common adverse effects in the intent to treat group were diarrhea (10.3%), neutropenia (6.4%) and elevation in alanine aminotransferase (6.4%).

CONCLUSIONS

Linezolid was well-tolerated and could be considered an alternative to vancomycin for treating serious infections caused by antibiotic-resistant Gram-positive cocci in children pending results of additional studies.

Arthralgias and myalgias related to quinupristin-dalfopristin administration

This study evaluated the frequency of and potential risk factors for arthralgias and/or myalgias associated with quinupristin-dalfopristin administration. Of 32 patients who received quinupristin-dalfopristin treatment, at least 15 (47%) developed arthralgias and/or myalgias. Clinicians should be aware of these adverse events associated with quinupristin-dalfopristin, which may occur more frequently than has been previously reported.

Novel streptogramin antibiotics

Streptogramins represent a unique class of antibiotics remarkable for their antibacterial activity and their unique mechanism of action. These antibiotics are produced naturally as secondary metabolites by a number of Streptomyces species and have been classified into two main groups. They consist of at least two structurally unrelated compounds, group A or M (macrolactones) and group B or S (cyclic hexadepsipeptides). Both groups bind bacterial ribosomes and inhibit protein synthesis at the elongation step and they act synergistically in vitro against many microorganisms. Streptogramins A and B act synergistically in vivo; the mixture of the two compounds is more powerful than the individual components and their combined action is irreversible. The pharmacokinetic parameters of group A and B streptogramins in blood are similar. The major gap, limiting the therapeutic use of the natural compounds, was represented by the lack dissolution in water. The synthesis of water-soluble derivatives of pristinamycin I(A) and II(B) has allowed the development of injectable, first represented by quinupristin/dalfopristin (Synercid) and oral formulations, represented by RPR-106972, streptogramins with fixed compositions. Streptogramins have demonstrated activity against Gram-positive microorganisms in vitro and in vivo, including those with multi-drug resistance. Moreover, the absence of cross-resistance to macrolides in many of these microorganisms and the rarity of cross-resistance between the two groups of antibiotics associated with the rapid bacterial killing are the principal features of the streptogramins, offering the possibility for treating the rising number of infections that are caused by multi-resistant Gram-positive bacteria.

Quinupristin/dalfopristin: a therapeutic review

BACKGROUND

The proliferation of multidrug-resistant gram-positive bacteria, including methicillin-resistant Staphylococcus aureus and vancomycin-resistant Enterococcus faecium (VREF), has created a pressing need for effective alternative antibiotics. Quinupristin/dalfopristin is a new combination streptogramin product with a selective spectrum of antibacterial activity, mainly against gram-positive aerobic bacteria. It has been assessed primarily in emergency-use protocols, in hospitalized patients with skin and skin-structure infections, and in patients with VREF bacteremia.

OBJECTIVES

The objectives of this review were to summarize important results of in vitro microbiologic studies; to provide information on relevant pharmacokinetic parameters, drug interactions, and Y-site compatibility; and to assess efficacy and safety data from clinical studies of quinupristin/dalfopristin.

METHODS

Articles included in this review were identified by a MEDLINE search of the literature published between 1966 and September 2000 using the terms Synercid, quinupristin, and dalfopristin. Additional articles were retrieved from the reference lists of articles identified in the MEDLINE search.

RESULTS

In vitro analysis of the spectrum of activity of quinupristin/dalfopristin has confirmed its relatively selective coverage of gram-positive aerobic bacteria. Both quinupristin and dalfopristin undergo hepatic metabolism and are extensively excreted in the feces. Combination quinupristin/dalfopristin inhibits the cytochrome P450 3A4 pathway, and caution is warranted with concomitant use of other medications eliminated via this pathway. In trials in patients with VREF infections, treatment success with quinupristin/dalfopristin varied depending on the site of infection, ranging from 51.9% in bacteremia of unknown origin to 88.9% in urinary tract infections. The results of comparative clinical trials suggest that quinupristin/dalfopristin has similar efficacy to that of commonly used antibiotics, including cefazolin, oxacillin, and vancomycin, in patients with skin and skin-structure infections or nosocomial pneumonia. The most frequently reported adverse effects with administration of quinupristin/dalfopristin were infusion-site inflammation, pain, and edema; other infusion-site reactions; and thrombophlebitis. Arthralgia, myalgia, nausea, diarrhea, vomiting, and rash occurred in 2.5% to 4.6% of patients and were the most frequently reported systemic adverse events.

CONCLUSIONS

Outcomes data from clinical trials indicate that quinupristin/dalfopristin has the potential to play an important role in the treatment of bacteremia, complicated skin and skin-structure infections, and nosocomial pneumonia caused by VREF. Issues of bacterial resistance to quinupristin/dalfopristin and other appropriate uses of this combination agent remain to be elucidated.

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.

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.

Effect of subinhibitory antibiotic concentrations on polysaccharide intercellular adhesin expression in biofilm-forming Staphylococcus epidermidis

Biofilm production is an important step in the pathogenesis of Staphylococcus epidermidis polymer-associated infections and depends on the expression of the icaADBC operon leading to the synthesis of a polysaccharide intercellular adhesin. A chromosomally encoded reporter gene fusion between the ica promoter and the beta-galactosidase gene lacZ from Escherichia coli was constructed and used to investigate the influence of both environmental factors and subinhibitory concentrations of different antibiotics on ica expression in S. epidermidis. It was shown that S. epidermidis biofilm formation is induced by external stress (i.e., high temperature and osmolarity). Subinhibitory concentrations of tetracycline and the semisynthetic streptogramin antibiotic quinupristin-dalfopristin were found to enhance ica expression 9- to 11-fold, whereas penicillin, oxacillin, chloramphenicol, clindamycin, gentamicin, ofloxacin, vancomycin, and teicoplanin had no effect on ica expression. A weak (i.e., 2.5-fold) induction of ica expression was observed for subinhibitory concentrations of erythromycin. The results were confirmed by Northern blot analyses of ica transcription and quantitative analyses of biofilm formation in a colorimetric assay.

New Gram-positive agents in nosocomial infection

Multidrug-resistant Gram-positive pathogens such as vancomycin-resistant enterococci, methicillin-resistant Staphylococcus aureus, and methicillin-resistant coagulase-negative staphylococci account for a significant number of nosocomial infections, and new options for therapy have been lacking. During the past year, two agents have been released that have activity against these organisms: quinupristin/dalfopristin and linezolid. Although neither agent is a panacea, these recently released agents offer new options for therapy.

New agents for Gram-positive bacteria

Infections caused by multiple-resistant Gram-positive organisms continue to occur at an alarming rate worldwide. Two new and unique antimicrobial agents targeted specifically against such organisms, quinupristin/dalfopristin and linezolid, have been approved for use in the USA in the past year and will play an important role in the treatment of life-threatening infections. In addition, several new fluoroquinolones have been approved recently or will be available in the near future to aid in the treatment of infections caused by resistant strains of Streptococcus pneumoniae.

Nationwide German multicenter study on prevalence of antibiotic resistance in staphylococcal bloodstream isolates and comparative in vitro activities of quinupristin-dalfopristin

Antibiotic-resistant gram-positive bacteria have become an increasing problem in the last two decades. In order to evaluate the prevalence of antibiotic resistance in staphylococcal bloodstream isolates in Germany, 2,042 staphylococci collected in 21 tertiary-care hospitals were investigated during a 3-year period (March 1996 to March 1999). Altogether, 1,448 S. aureus isolates and 594 coagulase-negative staphylococci (CoNS) that comprised 13 different species were included. Furthermore, the antistaphylococcal activities of quinupristin-dalfopristin were compared with those of eight other compounds by the broth microdilution method. The rates of oxacillin resistance in Staphylococcus aureus, S. epidermidis, S. haemolyticus, and other CoNS were 13.5, 69, 90, and 34%, respectively. In oxacillin-resistant strains high rates of resistance (up to 100%) to erythromycin, clindamycin, ciprofloxacin, and gentamicin were also observed. However, no strain appeared to be resistant to vancomycin or quinupristin-dalfopristin. The streptogramin combination exhibited excellent in vitro activity against all staphylococcal species tested, regardless of the patterns of resistance to other drug classes. In terms of MICs at which 90% of the isolates are inhibited, quinupristin-dalfopristin was 2 times more active against S. aureus isolates, 4 to 16 times more active against S. haemolyticus, and 8 to 32 times more active against S. epidermidis than vancomycin or teicoplanin.

Characterization of isolates associated with emerging resistance to quinupristin/dalfopristin (Synercid) during a worldwide clinical program

Quinupristin/dalfopristin (Synercid) is an i.v. antibiotic active against serious Gram-positive infections. Its unique dual mode of action means that the potential for resistance development is expected to be low. To determine the incidence of in vitro emerging resistance in worldwide clinical studies, susceptibility to quinupristin/dalfopristin was measured for baseline pathogens and corresponding on- or post-study isolates from 880 evaluable patients. In comparative studies of community-acquired pneumonia, complicated skin and skin structure infections, and nosocomial pneumonia, the incidence of emerging resistance was low (1 of 453; 0.22%; 95% CI: 0. 01-1.4%). Resistance development occurred in only one pathogen (methicillin-resistant Staphylococcus aureus). In noncomparative studies, six instances (1.8% of 338 evaluable cases; 95% CI: 0.7 to 4.0%) of emerging resistance (all vancomycin-resistant Enterococcus faecium) were confirmed, accompanied by therapeutic failure in four cases. Molecular typing did not confirm the identity of one pair of strains. Overall, the incidence of emerging resistance to quinupristin/dalfopristin was low.

Quinupristin-Dalfopristin

The incidence of infection with multidrug-resistant or pan-resistant gram-positive bacteria has drastically limited or eliminated the conventional antimicrobial options available to clinicians. Quinupristin-dalfopristin, a unique parenteral streptogramin that lacks cross-resistance with other antimicrobials, has shown clinical efficacy against many of these important bacteria. This review focuses on quinupristin-dalfopristin"s mechanism of action, in vitro spectrum of activity, clinical efficacy and toxicity, and likely future role in the management of serious gram-positive infections.

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.