Advances in the management of Pseudomonas aeruginosa infections in cancer patients

Multidrug-resistant Enterobacteriaceae, Pseudomonas aeruginosa, and vancomycin-resistant Enterococcus: Three major threats to hematopoietic stem cell transplant recipients

Hematopoietic stem cell transplant (HSCT) recipients are uniquely threatened by the emergence of multidrug-resistant (MDR) bacteria because these patients rely on immediate active antimicrobial therapy to combat bacterial infections. This review describes the epidemiology and treatment considerations for three challenging MDR bacterial pathogens in HSCT recipients: MDR Enterobacteriaceae, including extended-spectrum β-lactamase (ESBL)-producing and carbapenem-resistant Enterobacteriaceae (CRE), Pseudomonas aeruginosa, and vancomycin-resistant Enterococcus (VRE). These bacteria are common causes of infection in this population and bacteremias caused by these organisms are associated with high mortality rates. Carbapenems remain the treatments of choice for serious infections due to ESBL-producing Enterobacteriaceae in HSCT recipients. Administration of β-lactam agents as an extended infusion is associated with improved outcomes in patients with severe infections caused by P. aeruginosa. Older agents used for the treatment of CRE and MDR P. aeruginosa infections, such as polymyxins and aminoglycosides, have major limitations. Newer agents, such as ceftazidime-avibactam and ceftolozane-tazobactam have great potential for the treatment of Klebsiella pneumoniae carbapemenase-producing CRE and MDR P. aeruginosa, respectively, but more pre-clinical and clinical data are needed to better evaluate their efficacy. Daptomycin dosages ≥8 mg/kg/day are recommended to treat VRE infections in this population, particularly in the setting of increasing daptomycin resistance. Strategies to prevent these infections include strict adherence to recommended infection control practices and multidisciplinary antimicrobial stewardship. Last, gastrointestinal screening to guide empirical therapy and the use of polymerase chain reaction-based rapid diagnostics may decrease the time to administration of appropriate therapy for these infections, thereby leading to improved outcomes.

The growing threat of multidrug-resistant Gram-negative infections in patients with hematologic malignancies

Prolonged neutropenia and chemotherapy-induced mucositis render patients with hematologic malignancies highly vulnerable to Gram-negative bacteremia. Unfortunately, multidrug-resistant (MDR) Gram-negative bacteria are increasingly encountered globally, and current guidelines for empirical antibiotic coverage in these patients may not adequately treat these bacteria. This expansion of resistance, coupled with traditional culturing techniques requiring 2-4 days for bacterial identification and antimicrobial susceptibility results, have grave implications for these immunocompromised hosts. This review characterizes the epidemiology, risk factors, resistance mechanisms, recommended treatments, and outcomes of the MDR Gram-negative bacteria that commonly cause infections in patients with hematologic malignancies. We also examine the infection prevention strategies in hematology patients, such as infection control practices, antimicrobial stewardship, and targeted decolonization. Finally, we assess the strategies to improve outcomes of the infected patients, including gastrointestinal screening to guide empirical antibiotic therapy, new rapid diagnostic tools for expeditious identification of MDR pathogens, and use of two new antimicrobial agents, ceftolozane/tazobactam and ceftazidime/avibactam.

The global challenge of carbapenem-resistant Enterobacteriaceae in transplant recipients and patients with hematologic malignancies

Carbapenem-resistant Enterobacteriaceae (CRE) are emerging global pathogens. The spread of CRE to transplant recipients and patients with hematologic malignancies has ominous implications. These patients rely on timely, active antibacterial therapy to combat gram-negative infections; however, recommended empirical regimens are not active against CRE. Approximately 3%-10% of solid organ transplant (SOT) recipients in CRE-endemic areas develop CRE infection, and the infection site correlates with the transplanted organ. Mortality rates associated with CRE infections approach 40% in SOT recipients and 65% in patients with hematologic malignancies. Given that the current antimicrobial armamentarium to combat CRE is extremely limited, a multifaceted approach that includes antimicrobial stewardship and active surveillance is needed to prevent CRE infections in immunocompromised hosts. Improving outcomes of established infections will require the use of risk factor-based prediction tools and molecular assays to more rapidly administer CRE-active therapy and the development of new antimicrobial agents with activity against CRE.

The Norwegian experience with penicillin G plus an aminoglycoside as initial empiric therapy in febrile neutropenia; a review

BACKGROUND

The occurrence of antibiotic resistance and the use of broad-spectrum antibiotics are relatively low in Norway. The national recommendation in febrile neutropenia (FN) is prompt initial therapy with penicillin G plus an aminoglycoside. We sought to evaluate the evidence behind this recommendation.

METHODS

We did a literature search in Medline and EMBASE with search terms penicillin, aminoglycoside and febrile neutropenia.

RESULTS

Seven Norwegian studies (six adult and one pediatric) conducted over the last 25 years were identified. They all conclude that penicillin G plus an aminoglycoside are effective and safe initial empiric antibiotic therapy in FN provided the regimen is modified if the clinical response is unsatisfactory. Overall 40-50% of the patients required only penicillin G and an aminoglycoside during their FN episode. The overall fatality rate was similar in the Norwegian and in international studies.

CONCLUSION

Many countries use a broad-spectrum β-lactam as initial therapy in FN. International experts are sceptic towards the Norwegian recommendations. We discuss the arguments for and against penicillin G plus an aminoglycoside in FN. The main arguments to continue the Norwegian treatment tradition are the satisfactory clinical results and the reason to believe that it contributes to the low levels of antibiotic resistance in Norway.

Tobramycin once versus three times daily, given with penicillin G, to febrile neutropenic cancer patients in Norway: a prospective, randomized, multicentre trial

OBJECTIVES

Penicillin G with an aminoglycoside is the standard initial empirical treatment in febrile neutropenia in Norway. It has been argued that giving the aminoglycoside once daily to neutropenic patients with Gram-negative bacteraemia may be hazardous when penicillin G is the beta-lactam antibiotic. We questioned this argument and hypothesized that tobramycin once daily was as efficacious as three times daily.

METHODS

We conducted a randomized prospective multicentre study, comparing the efficacy of tobramycin 6 mg/kg once (arm A) versus three times (arm B) daily, plus penicillin G 5 million IU x 4, in febrile neutropenic cancer patients.

PRIMARY OUTCOME

modification of the antibiotic regimen.

RESULTS

One hundred and seventy-four patients were evaluable for intention-to-treat analyses. One hundred and fifty-five patients had lymphoma or leukaemia as the underlying cancer diagnosis. In arm A, 35 of 88 patients and in arm B, 34 of 86 patients, that is 40% in both arms had no modification of the antibiotic regimen. No patients died while participating in the study. Upon modification of the antibiotic regimen, all patients were successfully treated. The increase in serum creatinine was modest and similar in the two treatment groups.

CONCLUSIONS

When administered with penicillin G, tobramycin given once daily was as efficacious and safe as tobramycin given three times daily in cancer patients with febrile neutropenia in Norway, provided the regimen was modified according to the clinical response.

Interventional antimicrobial therapy in febrile neutropenic patients

In febrile neutropenic patients, prompt empiric antimicrobial intervention is mandatory. Numerous studies have demonstrated the benefit of broad-spectrum beta-lactams active against Gram-negative aerobes as well as against streptococci and Staphylococcus aureus in this setting. With this interventional strategy, a reduction of infection-related mortality to < or = 10% of patients undergoing intensive remission induction or consolidation chemotherapy could be obtained. Thereby, subgroups of patients have been identified who require an empiric modification of antimicrobial treatment, e.g., patients with catheter-related infections, with pulmonary infiltrates, or with unexplained fever (FUO) not responding to first-line antibacterials. In two consecutive, prospectively randomized trials conducted by the German Paul Ehrlich Society it could be shown that empiric antifungal therapy is beneficial for second-line treatment in patients with persistent FUO and improves first-line treatment results in patients with lung infiltrates. The addition of glycopeptides, however, should be restricted to patients with catheter-related infections due to coagulase-negative staphylococci or with infections due to multiresistant Gram-positive pathogens.

Occurrence of a 29 kDa polysaccharide in the slime layer of both smooth and rough strains of Pseudomonas aeruginosa

1. The lipopolysaccharide (LPS) and the extracellular products (slime) of a smooth, nonmucoid Pseudomonas aeruginosa strain (PAC IR) and its rough mutant (PAC 605) were subjected to a comparative biochemical analysis. 2. Chemical and electrophoretic analyses suggested that the slime preparation of both strains are composed mainly of similar carbohydrate components which are different from those of the respective lipopolysaccharides. 3. Chromatographic analysis of the two slime preparations on gel permeation HPLC columns revealed the presence of a major polysaccharide in both strains with an apparent molecular weight 29 kDa and a minor high molecular weight polysaccharide in the PAC IR strain.

Antibacterial therapy in patients with malignancies

Patients with malignant disease may be predisposed to bacterial infections because of neoplastic disruption of normal tissue barriers, exogenous immunosuppressive therapy (drugs with or without radiation), and intrinsic host immune deficits secondary to these diseases. Diminished polymorphonuclear leukocyte numbers or function and impaired humoral immunity are highly correlated with the development of serious bacterial infections. The usual signs and symptoms of infection may be absent or altered in a compromised host. Therapy must be instituted promptly upon clinical suspicion of bacterial infection, and empirical choices should usually include combinations that are synergistic for likely pathogens based on knowledge of the local predominant flora and susceptibility data. Synergism has most often been demonstrated in combinations that utilize a beta-lactam (semisynthetic penicillin or cephalosporin) and an aminoglycoside. Triple drug therapy has not been shown to be advantageous. Monotherapy with third generation cephalosporins, carbapenems, monobactams, or ureidopenicillins has not been proven to offer advantages over 2-drug regimens for these patients. Patients with blood deficient in granulocytes (granulocytopenic) who respond to 2-drug therapy but remain deficient in neutrophils (neutropenic) may need continued treatment until the neutropenia subsides. Those who do not respond and remain febrile with an unclear focus of infection may need to be started on antifungal therapy in addition to the antibacterial agent. The use of oral agents for the prophylaxis of neutropenic patients against bacteremia remains controversial. If drugs are used, co-trimoxazole and nystatin suspension may be preferable.

Bacteremia and fungemia in patients with neoplastic disease

This study reviewed 431 episodes of septicemia occurring in 356 patients with cancer at Memorial Sloan-Kettering Cancer Center during 1982. The most frequent organisms causing 273 episodes in 239 non-neutropenic patients were Escherichia coli (20 percent), Staphylococcus aureus (13 percent), polymicrobic (12 percent), Pseudomonas species (8 percent), Klebsiella species (7 percent), Candida species (7 percent), Bacteroides species (6 percent), Enterobacter species (4 percent), and Clostridium species (4 percent). The overall mortality was 31 percent (21 percent with adequate therapy; 50 percent with inadequate therapy). The most frequent organisms causing 158 episodes in 117 neutropenic patients were polymicrobic (21 percent), E. coli (16 percent), Klebsiella species (15 percent), Pseudomonas species (8 percent), Candida species (6 percent), S. aureus (6 percent), Streptococcus faecalis (5 percent), S. epidermidis (4 percent), and Corynebacterium CDC-JK (3 percent). The overall mortality was 52 percent (36 percent with adequate therapy; 88 percent with inadequate therapy). Since a review a decade ago, the spectrum of organisms changed in that the gram-positive organisms, S. faecalis, S. epidermidis, and C. CDC-JK, emerged as important pathogens. Neutropenic patients had a high incidence (42 percent) of septicemia due to multiple organisms, occurring concurrently or sequentially. The overall mortality of these patients was exceptionally high (80 percent). In contrast, the overall mortality of neutropenic patients with single-organism septicemia was comparable to that of non-neutropenic patients with single-organism septicemia (37 percent versus 29 percent).

Use of cephalosporins in the immunologically compromised patient

Infection is a major threat to patients with neutropenia, particularly those with haematological malignancies who are undergoing chemotherapy. Early use of an empirical antibiotic regimen with the broadest possible spectrum of activity is recommended until culture data can guide the choice. A standard combination in many centres is an amino-glycoside and a semisynthetic penicillin with antipseudomonal activity or a cephalosporin. However, no regimen can adequately cover all potential pathogens and in these patients, who are exposed to many toxic insults, the choice of antibiotics may significantly increase the incidence of side effects, particularly nephrotoxicity. There has, therefore, been considerable interest in simpler, less toxic (and less expensive) regimens and the concept of monotherapy has been explored. Although recent studies using ceftazidime alone have supported this as an effective approach, there remain several issues to resolve; and on a more cautionary note preliminary results from the latest EORTC study, which recruited more than 1200 patients, suggest that in Gram-negative bacteraemia, conventional combination therapy remains the treatment of choice in neutropenia. While monotherapy is attractive in an environment of low drug resistance when exposure to third generation cephalosporins is infrequent, this is rarely the case. In addition, the widespread use of tunnelled catheters for venous access had led to an increase in Gram-positive infections, and the more intensive immunosuppression to the emergence of fungal infections. Although these tend not to be rapidly fatal, their presence must be considered in designing treatment strategies. The influence of the host and treatment on the type of infection and the relative merits of the differing concepts in therapy are explored in detail in this article.

Serological failure of Pseudomonas vaccination in patients receiving multiple chemotherapy

Patients undergoing induction chemotherapy for malignant disease were immunized with a polyvalent Pseudomonas vaccine using a three or four dose schedule. A control group was immunized with a two dose schedule. Despite the more intensive administration of vaccine to the patients they produce a markedly subnormal and brief antibody response. A large clinical trial of this vaccine in patients with cancer seems unjustified in light of these data.

Quantitative determination of the effect of granulocytes on the course of experimental infections during antibiotic treatment

We are presenting a quantitative determination of the effect of granulocytes, monocytes and lymphocytes on the course of infection during antibiotic treatment. The animal model was a short-term infection of the thigh muscle in normal or irradiated mice. Two kinds of antibiotics were used: tobramycin for Pseudomonas aeruginosa infections and ampicillin for Escherichia coli infections. The number of granulocytes was changed by irradiating the mice before they were infected. The dose-effect relations for both combinations of bacteria and antibiotics were determined on various days after irradiation. Analysis of the results shows that the effect of an antibiotic was predominantly potentiated by granulocytes. This means that under the conditions of granulopenia, the dose of an antibiotic must be increased to obtain the same antibacterial effect. The present results indicate that the interrelation between host factors, bacterial proliferation and antibiotic treatment can be quantitated and may offer a useful model for screening antimicrobial drugs before they are clinically applied.

Therapy with antibiotics in leukemic patients

The recovery of an adequate granulocyte count after chemotherapy is the most important prognostic factor in neutropenic patients. In granulocytopenic patients, the risk of infection is very high and its course usually severe. Empiric antibiotic treatment must be started as soon as fever rises and blood cultures have been taken. The combination of an anti-pseudomonas penicillin with an aminoglycoside is presently the standard empiric therapy for febrile granulocytopenic patients. If the clinical response is inadequate, antimicrobial therapy should be adjusted to a bactericidal activity of greater than 1:16 in the serum. If antibiotic therapy fails, a fungal infection should be considered and amphotericin B added empirically. Patients must be closely supervised for superinfections. Therapeutic transfusions of granulocytes have proven useful in severe granulocytopenia and when antibiotic therapy has failed.

Safety and immunogenicity of high molecular weight polysaccharide vaccine from immunotype 1 Pseudomonas aeruginosa

The safety and immunogenicity of a high molecular weight polysaccharide from immunotype 1 Pseudomonas aeruginosa were tested in a dose response fashion in adult volunteers. The vaccine lacked toxicity and pyrogenicity for experimental animals. Doses of 50, 75, 150, or 250 microgram were given to groups of individuals as a single dose subcutaneous injection. Doses of 150 and 250 microgram were associated with a significant rise in binding and opsonic antibody at 2 wk postimmunization. Titers remained unchanged for up to 6 mo. The vaccine was almost devoid of toxicity, eliciting no more than a slightly sore and tender arm at the site of injection. High molecular weight polysaccharide antigen appears to induce a good immune response following vaccination that is effective in mediating opsonophagocytic killing of live P. aeruginosa organisms.

Antibacterial efficacy of cefazolin and cephradine in neutropenic mice

The activity of cefazolin (CEZ) and cephradine (CED) was studied in experimentally infected neutropenic mice. Neutropenia was induced by 600 rad whole-body irradiation; an infection was induced by the injection of 5 X 10(6) Escherichia coli into the thigh on Day 5 after irradiation. Antibiotics were administered 1 h later, and antibacterial activity was estimated from bacteria counts made in the homogenized individual thighs 3 h after infection. The effect of a low dose of each of the cephalosporins on the infection was significantly lower in the absence of granulocytes than in animals with intact host defence; at higher dosages the effect of both antibiotics on the infection was the same in neutropenic and unirradiated mice. In the neutropenic mice, CEZ was 2.95 times more active than CED against E. coli in vivo, this difference in activity being similar to that found earlier in normal mice.

Amikacin in the treatment of genito-urinary tract infections in cancer patients

Amikacin was used in the treatment of severe urinary tract infections in twenty-five seriously ill patients. In twenty-four of the patients, cystitis or pyelonephritis complicated carcinoma of the bladder. Structural changes in the urinary tract, resulting from schistosomiasis, presented additional obstacles to treatment in many of the patients. The most commonly isolated pathogens were Escherichia coli and Pseudomonas. Most patients received 500 mg of amikacin every twelve hours. Three patients experienced adverse renal reactions which showed subsequent improvement. Amikacin effected twenty-one (84%) complete cures and four (16%) clinical cures in the twenty-five patients. This represents 100% clinical success in this study.

Ticarcillin: pharmacokinetics in man according to different administration schedules

The pharmacokinetic characteristics of ticarcillin, a semisynthetic penicillin more active than carbenicillin against Pseudomonas, were studied. Following a rapid intravenous infusion of 1 g, 2 g, 5 g and 10 g ticarcillin respectively the serum half-life was 72-4 minutes independent of the dosage administered. If ticarcillin is administered under steady-state conditions, e.g. continuous infusion of either 2g/hr or 1g/hr following a loading dose of 1g (total dose 5 g) the average steady-state serum concentrations are 125 microgram/ml and 105 microgram/ml respectively.

Synergistic activity of carbenicillin and gentamicin in experimental Pseudomonas bacteremia in neutropenic rats

Rats made neutropenic with cyclophosphamide were infected intraperitoneally with Pseudomonas aeruginosa. The challenge organism was killed synergistically in vitro by the combination of gentamicin and carbenicillin. Untreated neutropenic rats infected with 3 x 10(6)Pseudomonas died between days 2 and 7, and the overall mortality was 70%. Groups of infected neutropenic rats were treated intramuscularly with 1.5 or 6 mg of gentamicin per kg per dose, 100 or 400 mg of carbenicillin per kg per dose, or 1.5 mg of gentamicin and 100 mg of carbenicillin per kg per dose. Treatment was begun at 2 h postinfection and was continued every 8 h for about 72 h. Cultures of blood and peritoneal washings were performed in control and treated rats at 1, 4, 24, 48, and 72 h postinfection. Gentamicin at either dose level was ineffective in preventing death, but mortality was significantly reduced by high-dose carbenicillin and low-dose combination therapy. In addition, the latter regimens sterilized the peritoneal fluid and blood. Carbenicillin and gentamicin showed in vivo synergy in the treatment of neutropenic Pseudomonas-infected rats.

Interaction of purulent material with antibiotics used to treat Pseudomonas infections

To define factors contributing to the adverse prognosis of patients with gram-negative bacillemia and abscess formation, we studied the interaction between polymyxin B, colistin sulfate, gentamicin, or carbenicillin with purulent material. Carbenicillin activity was not significantly altered by incubation with pus. Equal volumes of antibiotic and purulent sediment decreased the effective concentration of polymyxin B, colistin sulfate, or gentamicin from 100 mug/ml to 3 to 6 mug/ml. One milliliter of purulent sediment bound more than 700 mug of gentamicin and 1,500 mug of polymyxin B or colistin sulfate. This effect occurred rapidly, proceeded at 4 and 37 C, was stable for 24 to 48 h, and was altered, but not abolished, by varying the pH of the solution. Antibiotic activity could be removed from pus by high concentrations of protamine sulfate, heparin, sodium chloride, or potassium chloride, suggesting binding rather than inactivation.