Severe reversible reticulocytopenic anemia associated with quinupristin/dalfopristin RP59500 therapy

Quinupristin-dalfopristin and linezolid: evidence and opinion

Quinupristin-dalfopristin and linezolid demonstrate in vitro activity against a wide range of gram-positive bacteria, including many isolates resistant to earlier antimicrobials. Quinupristin-dalfopristin is inactive against Enterococcus faecalis but has been effective for treatment of infections due to vancomycin-resistant Enterococcus faecium associated with bacteremia. In comparative trials, linezolid proved to be equivalent to comparator agents, resulting in its approval for several clinical indications. The almost-complete bioavailability of linezolid permits oral administration. Each agent can cause adverse effects that may limit use in individual patients. Resistance to these drugs has been encountered infrequently among vancomycin-resistant E. faecium. Resistance to quinupristin-dalfopristin is rare among staphylococci in the United States, and resistance to linezolid is very rare. Whether there is any benefit to use of these agents in combination regimens, and whether there are circumstances in which they might be alternatives to cell-wall active antibiotics for treatment of bone or endovascular infections, are questions that deserve further study.

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.