Interactions of quinupristin-dalfopristin with eight other antibiotics as measured by time-kill studies with 10 strains of Staphylococcus aureus for which quinupristin-dalfopristin alone was not bactericidal

Limitations of antibiotic options for invasive infections caused by methicillin-resistant Staphylococcus aureus: is combination therapy the answer?

Invasive infections caused by methicillin-resistant Staphylococcus aureus (MRSA), particularly those involving persistent bacteraemia, necrotizing pneumonia, osteomyelitis and other deep-seated sites of infections, are associated with high mortality and are often difficult to treat. The response to treatment of severe MRSA infection with currently available antibiotics active against MRSA is often unsatisfactory, leading some physicians to resort to combination antibiotic therapy. Now, with the emergence of community-associated MRSA (CA-MRSA) clones that display enhanced virulence potentially related to up-regulated toxin production, the use of adjuvant protein synthesis-inhibiting antibiotics to reduce toxin production also has been advocated by some experts. In this review, we discuss the limitations of antibiotics currently available for the treatment of serious invasive MRSA infections and review the existing literature that examines the potential role of combination therapy in these infections.

In vitro combinations of five intravenous antibiotics with dalfopristin-quinupristin against Staphylococcus aureus in a 3-dimensional model

We compared the in vitro activity of dalfopristin and quinupristin combined with five intravenous antibiotics in a 3-dimensional model. We tested six strains of Staphylococcus aureus selected with different patterns of resistance to methicillin and erythromycin. Dalfopristin and quinupristin displayed a very synergistic activity against all the strains with a mean 16- or 32-fold decrease of inhibitory concentrations in combination. That synergy was even better against erythromycin-resistant strains. In combination with tigecycline or fosfomycin, the antibacterial activity could be consistently enhanced with the same decrease of inhibitory concentrations. A synergy was also observed, less regularly and at a lower level, with rifampin, gentamicin or vancomycin. Combinations of dalfopristin and quinupristin with tigecycline or fosfomycin could be very interesting in clinical practice because the inhibitory effect could be achieved with very low concentrations of each component, even when erythromycin-resistant strains are concerned.

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.

Methicillin-resistant Staphylococcus aureus: impact on dermatology practice

Methicillin (meticillin)-resistant Staphylococcus aureus (MRSA) emerged in the 1960s and is now commonly seen in hospitals, clinics and, since the mid-1990s, the community. Risk factors for the acquisition of MRSA include chronic dermatoses, underlying medical illnesses, attending healthcare facilities, use of prescription antibacterials, surgery, intravenous lines, hospitalization in an intensive care unit, and proximity to patients colonized with MRSA. Recent community-associated strains often occur in patients without these risk factors. Staphylococci are readily spread from person to person and readily contaminate the environment. Infection control measures thus involve identifying the infected patients, separating them from other non-infected patients, cleaning of the environment and, most important of all, scrupulous attention to hand hygiene. Alcoholic antiseptic hand rubs offer an alternative to antiseptic hand washes and increase compliance. Treatment of MRSA skin infections is challenging. Topical agents such as mupirocin or fusidic acid can be used, but the organisms often become resistant. Systemic therapy involves non-beta-lactams. Parenteral treatment is generally with glycopeptides such as vancomycin; oral therapy is more complex. Monotherapy with quinolones, rifampin (rifampicin), and fusidic acid often results in the development of resistance and so, if any of these agents are chosen it should be in combination. There are no data on combination therapy, although rifampin-containing combinations are often chosen. Fourth-generation quinolones and linezolid are expensive but promising alternatives.

Vancomycin resistance: occurrence, mechanisms and strategies to combat it

Vancomycin has long been considered the antibiotic of last resort against serious and multi-drug-resistant infections caused by Gram-positive bacteria. However, vancomycin resistance has emerged, first in enterococci and, more recently, in Staphylococcus aureus. Here, the authors attempt to review the prevalence and the mechanisms of such resistance. Furthermore, they focus on strategies that have been developed or are under current investigation to overcome infections caused by vancomycin-resistant strains. Among these are glycopeptide derivatives with higher potency than vancomycin, small molecules that resensitise bacteria to the antibiotic and novel non-glycopeptide antibiotics. These agents are targeted to interfere with protein and/or peptidoglycan (PG) synthesis and integrity or with membrane permeability. Whilst most of these agents are still in clinical or preclinical development, some have entered the clinic and currently represent the only option for treating vancomycin-resistant enterococci (VRE).

Efficacies of quinupristin-dalfopristin combined with vancomycin in vitro and in experimental endocarditis due to methicillin-resistant Staphylococcus aureus in relation to cross-resistance to macrolides, lincosamides, and streptogramin B- type antibiotics

A beneficial effect of the combination of quinupristin-dalfopristin and vancomycin was observed against two methicillin-resistant strains of Staphylococcus aureus harboring or not harboring the ermC gene, which codes for constitutive macrolide, lincosamide, and streptogramin B resistance. The beneficial effect was observed in time-kill studies, in which the drugs were used at inhibitory concentrations, and in a rabbit model of endocarditis, in which the combination was highly bactericidal and more active than monotherapies.

Quinupristin/dalfopristin bonding in combination with intraperitoneal antibiotics prevent infection of knitted polyester graft material in a subcutaneous rat pouch model infected with resistant Staphylococcus epidermidis

OBJECTIVE

to investigate the efficacy of quinupristin/dalfopristin in the prevention of prosthetic graft infection in a rat subcutaneous pouch model.

METHODS

graft infections were established in the subcutaneous tissue of 140 male Wistar rats by implantation of Dacron prostheses followed by topical inoculation with Staphylococcus epidermidis with intermediate resistance to glycopeptides. The study included one group without contamination, one contaminated group without prophylaxis, one contaminated group that received 50mg/l quinupristin/dalfopristin-soaked graft, one contaminated group that received 10mg/kg intraperitoneal levofloxacin, one contaminated group that received 3mg/kg intraperitoneal doxycycline, and two contaminated groups that received 50mg/l quinupristin/dalfopristin-soaked plus 10mg/kg intraperitoneal levofloxacin or 3mg/kg intraperitoneal doxycycline. Each group included 20 animals. The grafts were removed after 7 days and evaluated by quantitative culture.

RESULTS

quinupristin/dalfopristin showed a significantly higher efficacy than levofloxacin and doxycycline, even though quantitative graft cultures for rats that received only quinupristin/dalfopristin-soaked graft showed bacterial growth. Otherwise, the efficacy of levofloxacin was similar to that of doxycycline. Only the group treated with quinupristin/dalfopristin combined with levofloxacin or doxycycline showed no evidence of staphylococcal infection.

CONCLUSIONS

quinupristin/dalfopristin as adjunctive topical antibiotic prophylaxis can be useful for the prevention of vascular graft infections caused by staphylococcal strains with high levels of resistance.

Efficacy of quinupristin-dalfopristin in preventing vascular graft infection due to Staphylococcus epidermidis with intermediate resistance to glycopeptides

A rat model was used to investigate the efficacy of quinupristin-dalfopristin (Q-D) in the prevention of vascular prosthetic graft infection due to methicillin-resistant Staphylococcus epidermidis with intermediate resistance to glycopeptides. The in vitro activity of the compound was compared to that of vancomycin by MIC determination and time-kill study. Moreover, the efficacy of collagen-sealed Q-D-soaked Dacron was evaluated in a rat model of graft infection. Graft infections were established in the subcutaneous tissue of the backs of 120 adult male Wistar rats. The in vivo study included a control group, one contaminated group that did not receive any antibiotic prophylaxis, two contaminated groups that received grafts soaked with 10 and 100 micro g of Q-D per ml, respectively, and two contaminated groups that received grafts soaked with 10 and 100 micro g of vancomycin per ml, respectively. Rats that received Dacron grafts soaked with 100 micro g of Q-D per ml showed no evidence of infection (<10 CFU/ml). In contrast, for rats that received Dacron grafts soaked with 10 micro g of Q-D per ml and Dacron grafts soaked with 10 or 100 micro g of vancomycin per ml, the quantitative graft cultures demonstrated 2.2 x 10(2) +/- 1.3 x 10(2), 2.2 x 10(6) +/- 1.9 x 10(5), and 5.6 x 10(2) +/- 0.3 x 10(2) CFU/ml, respectively. Taken together the results of the study demonstrate that the use of Dacron grafts soaked with Q-D can result in significant bacterial growth inhibition and show that this compound is potentially valuable for prevention of vascular prosthetic graft infection.