Interaction between quinupristin/dalfopristin and cyclosporine

Diagnosis and management of community-associated MRSA infections in children

The history of antibiotic resistance in Staphylococcus aureus spans more than half a century. Methicillin-resistant S. aureus (MRSA) has emerged as an almost ubiquitous pathogen in both the community and hospital settings. The predominant clone responsible for community-associated MRSA, USA300, is a highly successful pathogen, as demonstrated by its rapid global spread and associated morbidity and mortality. The management of MRSA infections in pediatric patients is complicated by the limited number of effective antibiotics that have been well-studied in children. The gold standard antimicrobial, vancomycin, has several shortcomings that have prompted the development of newer agents for the treatment of MRSA disease. Moreover, the emergence of vancomycin-intermediate or -resistant S. aureus, while uncommon, portends a potential new era of resistance that will require research and development of the next generation of antibiotics that act by novel mechanisms.

New therapeutic choices for infections caused by methicillin-resistant Staphylococcus aureus

In recent years, a marked increase in the incidence of infections caused by methicillin-resistant Staphylococcus aureus (MRSA) has occurred in many countries. This review addresses the effectiveness and limitations of drugs classically used for the treatment of MRSA, e.g. vancomycin, and also newer anti-MRSA antimicrobials, e.g. second-generation glycolipopeptides, tigecycline, and beta-lactams.

Drug Interactions Between Antibiotics and Select Maintenance Medications: Seeing More Clearly Through the Narrow Therapeutic Window of Opportunity

OBJECTIVE

Infections often occur while treating patients with long-term medications for chronic illnesses. Treating these infections with systemic antibiotics often leads to pharmacokinetic and pharmacodynamic interactions between the antimicrobials and one or more of the maintenance medications. Previously optimized long-term regimens may become either subtherapeutic or super-therapeutic, with deleterious consequences. This article discusses some of the most significant and commonly encountered antibiotic drug interactions that may occur with medications with "narrow therapeutic windows" including warfarin, phenytoin, carbamazepine, theophylline, and the two calcineurin inhibitors. Given the logistics of many consultant pharmacists' practices, it may not always be possible for them to react prospectively when these combinations are prescribed at their facilities. Therefore, there are several things the pharmacist can do: provide regular and comprehensive inservice raining on this topic, be available as needed to answer patient-specific questions, and provide readily available charts and other educational materials that help identify and characterize these important interactions.

DATA SOURCES

A Medline search of the English literature was performed in October/November 2003, going back to 1980 for the commonly used antibiotics and drug interactions stated in this text. In some cases, cross referencing of articles reviewed also led to older publications. Textbooks dealing with drug interactions also were used as initial sources. However, whenever possible, any data quoted within the text were verified from the original research paper.

STUDY SELECTION

Pharmacokinetic studies, case reports, and general review articles published in the English medical literature were all selected for review. In cases where review articles were cited that summarize groups of data from previous original research papers, the authors made the best possible effort to verify the accuracy by referring to the original research papers.

DATA SYNTHESIS

Because of the breadth of the topic in terms of all the antibiotics discussed, the interacting medications that pertained to each antibiotic, and the lack of homogeneity among the various types of papers (most of which were case reports), most analyses include broad-based summaries based on the aggregate findings of the authors.

CONCLUSION

The addition of antibiotics to a stabilized medical regimen can result in either potentiation or antagonism of the clinical effects of narrow-therapeutic-window medications such as warfarin, phenytoin, theophylline, calcineurin inhibitors, carbamazepine, and numerous other agents. As usual in the clinical arena, awareness is the first step in appropriate management of these encounters.

Pharmacokinetics of Daptomycin in a Critically Ill Adolescent with Vancomycin-Resistant Enterococcal Endocarditis

Daptomycin is a lipopeptide antibiotic active against multidrug-resistant gram-positive organisms. Our search of the literature found no published pediatric pharmacokinetic data. We report the use of pharmacokinetic analysis of daptomycin in a 13-year-old boy with vancomycin-resistant Enterococcus faecium endocarditis. Pharamcokinetic parameters were found to be significantly different from published adult parameters, such as a faster elimination rate, shorter half-life, and increased clearance. These age-related differences in the pharmacokinetic profile of daptomycin have significant dosing implications. As the use of this drug for off-label indications and in pediatric populations increases, it is important for clinicians to better understand the drug's pharmacokinetic profile in these patient populations.

Safety of Newer Parenteral Antibiotics

Several parenteral antimicrobials have been introduced into clinical practice over the course of the last decade. Some of these agents (e.g., linezolid, daptomycin, and tigecycline) are prototypes of new classes of compounds. In comparative clinical trials, these newer anti-infectives have been shown to be safe and to have low rates of discontinuation by patients. However, long-term use has revealed unique toxicities associated with the use of some of these drugs. The adverse events and potential drug interactions associated with the use of these antibiotics are variable and require familiarity with the safety profile of each drug. It is especially important that clinicians be able to recognize serious adverse events associated with the use of specific drugs, because most of the adverse events can be readily reversed by cessation of therapy.

Drug interactions in the hematopoietic stem cell transplant (HSCT) recipient: what every transplanter needs to know

Pharmacokinetic drug interactions among hematopoietic stem cell transplant recipients can result in either increases in serum concentrations of medications, which may lead to enhanced toxicity; or reduced serum concentrations, which can lead to treatment failure and the emergence of post transplant complications. The use of drugs that have a narrow therapeutic index, such as cyclosporine/tacrolimus (calcineurin inhibitors), increases the significance of these interactions when they occur. This report will review the clinical data evaluating the drug interactions of relevance to HSCT clinical practice, focusing on the pharmacokinetic interactions, and provides recommendations for managing these interactions to avoid both toxicity and treatment failure.

Novel antibacterial agents for skin and skin structure infections

With the continuing development of clinical drug resistance among bacteria and the advent of resistance to the recently released agents quinupristin-dalfopristin and linezolid, the need for new, effective agents to treat multidrug-resistant gram-positive infections remains important. With treatment options limited, it has become critical to identify antibiotics with novel mechanisms of activity. Several new drugs have emerged as possible therapeutic alternatives. This review focuses on agents newly introduced and those presently in clinical development for the treatment of skin and skin structure infections. Linezolid, quinupristin-dalfopristin, and daptomycin have been approved by the Food and Drug Administration for the treatment of skin and skin structure infections. Two newer compounds, oritavancin and dalbavancin, are in clinical development for this indication. In addition, the quinolones moxifloxacin and gatifloxacin recently were approved for cutaneous infections.

LEARNING OBJECTIVE

At the conclusion of this learning activity, participants should be familiar with the modes of action, clinical indications, dosage regimens, and contraindications and cautions for several novel antibacterial agents for skin and skin structure infections.

Clinical pharmacokinetics of quinupristin/dalfopristin

Quinupristin/dalfopristin is a streptogramin antibacterial with a wide spectrum of Gram-positive antibacterial activity. The drug has minimal oral absorption and is administered intravenously as a fixed 30 : 70 ratio of quinupristin to dalfopristin. A linear relationship has been observed between the dose administered and maximum plasma concentrations. Single-dose administration of 7.5 mg/kg produced a maximal plasma concentration of 2.3-2.7 mg/L for quinupristin and 6.1-8.2 mg/L for dalfopristin. The area under the concentration-time curve (AUC) obtained with the same dose was 2.7-3.3 and 6.5-7.7 mg. h/L for quinupristin and dalfopristin, respectively. Repeated administration results in 13-21% increases in maximum plasma concentrations and 21-26% increases in AUC for both quinupristin and dalfopristin. Quinupristin and dalfopristin exhibit steady-state volumes of distribution of 0.46-0.54 and 0.24-0.30 L/kg, respectively. Quinupristin exhibits higher protein binding (55-78%) than dalfopristin (11-26%), though both entities distribute well into tissues. Concentrations exceeding those in blood have been reported for the kidney, liver, spleen, salivary glands and white blood cells of primates. Extravascular penetration, as measured in blister fluid, is 40-80%. Both quinupristin and dalfopristin are extensively metabolised via nonenzymatic reactions. Quinupristin is conjugated to form two active compounds, a cysteine moiety and a glutathione moiety. Dalfopristin is hydrolysed to the active metabolite pristinamycin IIA. The metabolites exert antibacterial activity similar to that of the parent compounds. Quinupristin/dalfopristin is excreted primarily in the faeces (75-77%), with lesser renal excretion (15-19%). The elimination half-lives of quinupristin and dalfopristin are similar, and are 0.7-1.3 hours after single doses. The metabolites have slightly longer half-lives, ranging from 1.2 to 1.8 hours. With repeated doses, plasma clearance of quinupristin and dalfopristin is reduced by approximately 20% compared with single doses, resulting in clearances of 0.7-0.8 L/h/kg. Saturable protein binding has been hypothesised as a causative mechanism. Quinupristin/dalfopristin is an inhibitor of cytochrome P450 3A4, resulting in multiple drug interactions. Ciclosporin AUC increased by 5-222% when coadministered with quinupristin/dalfopristin. Careful monitoring of patients receiving drugs that are substrates of cytochrome P450 3A4 is suggested.Quinupristin/dalfopristin is administered at 7.5 mg/kg every 8-12 hours, depending upon the severity of infection. The pharmacodynamic parameter linked with antibacterial activity for quinupristin/dalfopristin appears to be the ratio of AUC to the minimal inhibitory concentration. The additional activity of a prolonged post-antibiotic effect may also be important for efficacy.

New anti-Gram-positive agents

As the prevalence of resistant Gram-positive organisms in the critical care unit has increased, so have the associated morbidity and mortality and the cost of their treatment. As a result, more toxic and less active second-line agents and combinations of agents are used, often with limited evidence of clinical benefit. Although widely used, the role of glycopeptides is limited by increasing resistance and poor pharmacokinetics. New agents now in use, such as quinupristin/dalfopristin and Linezolid (Zyvox; Pharmacia & Upjohn, Kalamazoo, MI), show promise, as do diverse agents in development. The future is likely to bring greater therapeutic choice but, inevitably, further resistance.

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.

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.