Combination amphotericin B-rifampin therapy for pulmonary aspergillosis in a leukemic patient

Dual Inhibition of Klebsiella pneumoniae and Pseudomonas aeruginosa Iron Metabolism Using Gallium Porphyrin and Gallium Nitrate

Iron- and heme-uptake pathways and metabolism are promising targets for the development of new antimicrobial agents, as their disruption would lead to nutritional iron starvation and inhibition of bacterial growth. Salts of gallium(III) (Ga), an iron mimetic metal, disrupt iron-dependent biological processes by binding iron-utilizing proteins and competing with iron for uptake by bacterial siderophore-mediated iron uptake systems. Ga porphyrins, heme mimetic complexes, disrupt heme-utilizing hemoproteins. Because Ga(NO₃)₃ and Ga porphyrin disrupt different pathways of bacterial ion acquisition and utilization, we hypothesized that if used in combination, they would result in enhanced antimicrobial activity. Antimicrobial activity of Ga porphyrins (Ga protoporphyrin, GaPP, or Ga mesoporphyrin, GaMP) alone and in combination with Ga(NO₃)₃ were evaluated against Pseudomonas aeruginosa, Klebsiella pneumoniae, Acinetobacter baumannii, and methicillin-resistant Staphylococcus aureus (MRSA) under iron-limited conditions. The Ga porphyrin/Ga(NO₃)₃ combination demonstrated substantial synergism against K. pneumoniae, P. aeruginosa, and MRSA. Time-kill assays revealed that the synergistic combination of GaPP/Ga(NO₃)₃ was bacteriostatic against K. pneumoniae and MRSA and bactericidal against P. aeruginosa. The GaPP/Ga(NO₃)₃ combination significantly disrupted K. pneumoniae and P. aeruginosa biofilms on plasma-coated surfaces and increased the survival of Caenorhabditis elegans infected with K. pneumoniae or P. aeruginosa. When assessing the antibacterial activity of the Ga(III)/antibiotic combinations, GaPP/colistin and Ga(NO₃)₃/colistin combinations also showed synergistic activity against K. pneumoniae and P. aeruginosa. Our results demonstrate that GaPP and Ga(NO₃)₃ have significant synergistic effects against several important human bacterial pathogens through dual inhibition of iron and heme metabolism.

Synergism between Medihoney and rifampicin against methicillin-resistant Staphylococcus aureus (MRSA)

Skin and chronic wound infections caused by highly antibiotic resistant bacteria such as methicillin-resistant Staphylococcus aureus (MRSA) are an increasing and urgent health problem worldwide, particularly with sharp increases in obesity and diabetes. New Zealand manuka honey has potent broad-spectrum antimicrobial activity, has been shown to inhibit the growth of MRSA strains, and bacteria resistant to this honey have not been obtainable in the laboratory. Combinational treatment of chronic wounds with manuka honey and common antibiotics may offer a wide range of advantages including synergistic enhancement of the antibacterial activity, reduction of the effective dose of the antibiotic, and reduction of the risk of antibiotic resistance. The aim of this study was to investigate the effect of Medihoney in combination with the widely used antibiotic rifampicin on S. aureus. Using checkerboard microdilution assays, time-kill curve experiments and agar diffusion assays, we show a synergism between Medihoney and rifampicin against MRSA and clinical isolates of S. aureus. Furthermore, the Medihoney/rifampicin combination stopped the appearance of rifampicin-resistant S. aureus in vitro. Methylglyoxal (MGO), believed to be the major antibacterial compound in manuka honey, did not act synergistically with rifampicin and is therefore not the sole factor responsible for the synergistic effect of manuka honey with rifampicin. Our findings support the idea that a combination of honey and antibiotics may be an effective new antimicrobial therapy for chronic wound infections.

Rifampin combination therapy for nonmycobacterial infections

The increasing emergence of antimicrobial-resistant organisms, especially methicillin-resistant Staphylococcus aureus (MRSA), has resulted in the increased use of rifampin combination therapy. The data supporting rifampin combination therapy in nonmycobacterial infections are limited by a lack of significantly controlled clinical studies. Therefore, its current use is based upon in vitro or in vivo data or retrospective case series, all with major limitations. A prominent observation from this review is that rifampin combination therapy appears to have improved treatment outcomes in cases in which there is a low organism burden, such as biofilm infections, but is less effective when effective surgery to obtain source control is not performed. The clinical data support rifampin combination therapy for the treatment of prosthetic joint infections due to methicillin-sensitive S. aureus (MSSA) after extensive debridement and for the treatment of prosthetic heart valve infections due to coagulase-negative staphylococci. Importantly, rifampin-vancomycin combination therapy has not shown any benefit over vancomycin monotherapy against MRSA infections either clinically or experimentally. Rifampin combination therapy with daptomycin, fusidic acid, and linezolid needs further exploration for these severe MRSA infections. Lastly, an assessment of the risk-benefits is needed before the addition of rifampin to other antimicrobials is considered to avoid drug interactions or other drug toxicities.

Considerations in Clinical Trials of Combination Antifungal Therapy

The cure rate for serious fungal diseases with currently available agents used as monotherapy is not optimal. The introduction of new classes of antifungal drugs in the last few years naturally leads to the hypothesis that antifungal drugs used in combination may be more effective than the same drugs used alone. The design and interpretation of combination therapy studies raise challenges beyond those encountered when drugs are studied as monotherapy in the treatment of a disease. The definition of combination therapy, the study design, the selection of appropriate patient populations, and the selection of end points, as well as practical considerations, are all important in the design and interpretation of clinical trials of combination therapies. Although combination therapies hold the promise of improved efficacy, it is important to prove this hypothesis, because they also may be associated with increased toxicity and increased drug costs. A careful consideration of study design factors before the initiation of a trial will help obtain the most useful information for patients in this important area.

Interventional antimicrobial therapy in febrile neutropenic patients. Study Group of the Paul Ehrlich Society for Chemotherapy

In this prospective multicenter trial, treatment strategies for 1573 patients with neutropenia < 1000/microliters and fever > or = 38.5 degrees C after cytotoxic chemotherapy were compared. Patients with unexplained fever were randomized to a three-phase sequential study for different established drug regimens. If an infection could be defined microbiologically or clinically, treatment modifications were determined. In phase I, treatment for all patients consisted of acylaminopenicillin (PEN) plus aminoglycoside (AMG); or third-generation cephalosporin (CEPH) plus AMG; or PEN plus CEPH. In 800 patients with unexplained fever the response rates were: PEN/AMG (n = 258): 74.4%, CEPH/AMG (n = 252): 73.4%; PEN/CEPH (n = 290): 70.0%. Total response rate was 72.5%. In phase II, patients not responding after 3 days received PEN/CEPH/vancomycin (n = 70) or PEN/CEPH/AMG (n = 74). The respective response rates were 52.9% and 55.4%, total 54.2%. If fever did not resolve, the patients received either PEN/CEPH (n = 40) or imipenem/cilastatin (n = 59) both in combination with amphotericin-B/5-flucytosin/rifampin. The response rates were 62.5% and 79.7%, respectively (p = 0.07), total 72.7%. No significant differences between the treatment modalities compared were found. Analyzing all three phases together, 91.3% of patients with unexplained fever were cured. The response rate was also analyzed according to patients with gram-positive bacteremia (n = 183), response rate = 82.5%; gram-negative organisms (n = 145) 78.6%; fungemia (n = 51) 43.1% (p < 0.001); lung infiltrates (n = 269) 61.3% (p < 0.001); clinically documented infections (n = 198) 84.4%; and clinically and microbiologically documented infections (n = 84) 82.1%. If infections were diagnosed after at least 5 febrile days, more lung infiltrates and fungal infections occurred (p < 0.001). Leukocytes rising above 500/mu during the infection predicted better response rates (p < 0.001): in unexplained fever 97.8% vs 86.5% and lower death rates 1.5% vs 8.5%. In documented infections the response rates were then 89.9% vs 62.3% and the death rates 7.0% vs 20.5%. Therapy of neutropenic fever and infections must be adapted according to risk factors and should include early empiric antifungal therapy. The therapeutic and prophylactic use of hematopoietic growth factors to overcome neutropenia should be evaluated.

Pulmonary infiltrations in febrile patients with neutropenia. Risk factors and outcome under empirical antimicrobial therapy in a randomized multicenter study

BACKGROUND

Different empirical approaches to antimicrobial treatment of lung infiltrates in patients with neutropenia were studied within a prospective, randomized multicenter trial.

METHODS

Patients with neutropenia with hematologic malignancies and fever of 38.5 degrees C or higher associated with newly diagnosed lung infiltrates were randomized for an initial therapy with acylaminopenicillin plus aminoglycoside (Group A), third-generation cephalosporin plus aminoglycoside (Group B), or the double beta-lactam combination (Group C), each in combination with rifampin. Nonresponders were given empirical amphotericin B plus 5-fluorocytosine beginning on day 4, day 5, or day 6 under study.

RESULTS

Of 295 patients entered, 91.2% were evaluable. Complete response was obtained in 61.3% with no significant difference between treatment groups. The addition of rifampin did not improve treatment results. Only 27.1% of patients achieved a complete response by antibiotic therapy without additional antifungal therapy. Fungi dominated in cases of microbiologically documented infections and were associated with a poorer outcome compared with bacterial pneumonias. The trend of leukocyte counts under study had a highly significant effect on the outcome of infection.

CONCLUSIONS

Lung infiltrates in febrile patients with neutropenia represent a high risk of treatment failure. Persistent neutropenia has a significantly adverse effect on the outcome of infection. Incorporation of systemic antifungal agents into first-line therapy, particularly in selected high-risk subgroups, might improve future treatment results. The quality of diagnostic techniques to establish the etiology of pulmonary infiltrates needs to be improved.

Use of rifampin in nonstaphylococcal, nonmycobacterial disease

Rifampin has very broad antimicrobial properties with in vitro activities against many bacteria, mycobacteria, higher bacteria, chlamydia, fungi, parasites, and viruses (Table 1). The clinical use of rifampin is more limited, in part because of the lack of in vivo human clinical studies demonstrating its efficacy. Investigators have valid concerns regarding the emergence of resistance of mycobacteria if widespread use of rifampin becomes common, although this has not been well documented. Because rifampin obtains therapeutic levels intracellularly and is distributed widely throughout the body, the antibiotic potentially could be used on a broader scale, but more studies will be needed to demonstrate its clinical utility.

Synergistic action of amphotericin B and rifampin against Rhizopus species

A 16-year-old diabetic patient developed Rhizopus pneumonia and was initially treated with amphotericin B for 7 days. Because of clinical deterioration of the patient, rifampin was added empirically. The patient improved clinically, and lung tissue removed surgically 8 weeks later showed no fungal elements by histopathological studies or by culture. An in vitro study of amphotericin B alone and in combination with rifampin against the isolate from the patient and 11 additional isolates of Rhizopus spp. was designed. The activity of amphotericin B in the presence of rifampin (10 or 5 micrograms/ml) increased fourfold against 9 of 10 clinical and 1 of 2 environmental isolates. Amphotericin B activity in the presence of 2 micrograms of rifampin per ml increased fourfold against 6 of 10 clinical isolates and increased twofold against an additional 3 clinical isolates. Amphotericin B in the presence of 1 microgram of rifampin per ml inhibited 9 of 10 isolates at a concentration of one-half the MIC of amphotericin B alone. These findings were confirmed by dose-response curves calculated from fungal dry weight determinations of Rhizopus spp. incubated in serial dilutions of amphotericin B combined with rifampin. These observations demonstrate in vitro, and possibly in vivo, synergy between amphotericin B and rifampin against Rhizopus spp.

Serum fungistatic and fungicidal activity in volunteers receiving antifungal agents

The serum levels of two imidazoles, ketoconazole and Bayer n7133, when administered alone or in combination with rifampin, were measured in volunteers and the serum antifungal activity was determined against various fungal strains. Serum levels were measured by high pressure liquid chromatography and correlated with serum fungistatic activity as determined in microtiter plates. Ketoconazole showed a wide range of serum levels, suggesting individual variations. The addition of two doses of rifampin significantly decreased serum levels of both imidazoles and no synergism was observed. Serum fungicidal activity could only occasionally be demonstrated against one strain of Candida albicans and Candida stellatoidea. Serum fungistatic activity significantly correlated with the serum levels of both imidazoles. This approach should be investigated in patients to establish its potential clinical relevance for managing invasive fungal infections.

Parasitic adaptation of pathogenic fungi to mammalian hosts

Pathogenic fungi involved in medical and veterinary mycology can be classified in three different groups according to their level of adaptation to parasitism. Only a few species belonging to dermatophytes can be considered genuine parasites as opposed to molds or fungi involved in systemic mycoses. Ecological, ethological, biochemical, and immunological factors can play a role in preadaptation or adaptation to parasitic life and are discussed.

In vitro activities of amphotericin B in combination with four antifungal agents and rifampin against Aspergillus spp

Strains of Aspergillus fumigatus, Aspergillus flavus, and Aspergillus niger were tested for in vitro susceptibility with a microtiter plate system in buffered yeast-nitrogen base and in buffered minimal essential medium. Isolates were tested against amphotericin B, flucytosine, rifampin, ketoconazole, ICI 153,066, and Bay n 7133 and against combinations of amphotericin B with each of the other five drugs. Combinations of amphotericin B and rifampin were the most active against all three species of Aspergillus. Flucytosine combined with amphotericin B produced little or no reduction of the MICs at which 90% of the strains were inhibited compared with amphotericin B alone. With one exception, the addition of ketoconazole, ICI 153,066, or Bay n 7133 to amphotericin B did not consistently alter the MICs. The addition of ICI 153,066 markedly increased the MICs of amphotericin B against the A. flavus isolates in both media. When the azoles were tested alone, Bay n 7133 was the most active against A. fumigatus, but was two- to fivefold less active against A. flavus. Ketoconazole was the most active azole against A. flavus.

Growth inhibition of Leishmania tropica amastigotes in vitro by rifampicin combined with amphotericin B

Rifampicin and Amphotericin B (AMB) were studied separately and in combination to determine their effect in vitro on intracellular Leishmania tropica amastigotes. On the fourth day of treatment, rifampicin at 200 micrograms ml-1 or AMB at 0.15 microgram ml-1 reduced the parasites' survival index (PSI) to 10% compared with the untreated control. In combination, there was a significant synergistic effect at several concentrations. The synergistic therapeutic effects were not accompanied by toxicity to the host cells, although each drug alone caused cellular degeneration in the ultrastructure of the parasites with the formation of large autophagic-like vacuoles, while the combination increased the percentage of degenerate cells.

Antifungal chemotherapy

When the decision to treat a fungal infection is made, there are several antifungal agents available for use. AmB remains the first-line drug in the treatment of most systemic fungal infections. Miconazole should be used to treat patients who cannot tolerate AmB or who are infected with AmB-resistant organisms. Ketoconazole has a distinct advantage in that it is a relatively nontoxic oral agent and may prove very effective in treating non-life-threatening chronic fungal infections. Clinical experience with miconazole and ketoconazole is too limited at present to recommend them as first-line therapeutic agents, except in a limited number of clinical situations. 5-FC should only be used in combination with AmB to treat yeast infections.

Invasive aspergillosis of the lung and pericardium in a nonimmunocompromised 33 year old man

In a 33 year old man with no discernible immunologic defect, invasive aspergillosis developed in both the pericardium and lung with marked granulomatous reaction. The patient received 2 g of intravenous amphotericin B over eight weeks, with partial regression of the pulmonary infiltrate and disappearance of symptoms. However, five months later, he returned with marked progression of his disease. Evaluation of host defense, including granulocyte and lymphocyte function, was normal. The patient was given an additional 3g of amphotericin B over nine weeks with marked improvement in symptoms and chest roentgenogram. At six-month follow-up, he was asymptomatic with a stable radiographic appearance. A recurrence in symptoms and the pulmonary infiltrate was noted two months later. He was treated with an additional course of amphotericin and currently is receiving ketoconazole in hopes of suppressing the infection. We could find no immune impairment to explain the severe pulmonary and pericardial disease due to Aspergillus flavus in this young man.

Invasive aspergillosis with massive fatal hemoptysis in patients with neoplastic disease

Two patients had fatal episodes of massive hemoptysis secondary to invasive aspergillosis, complicating in one with acute leukemia and in the other with lung carcinoma. Review of the literature reveals that these cases are among the very few in which invasive aspergillosis has been documented as the etiology of massive hemoptysis in cancer patients. Both patients had been previously treated with corticosteroids and/or other immunosuppressive agents. In one of the two patients, the diagnosis was made ante mortem and antifungal therapy instituted, but dissemination progressed despite treatment.

Invasive aspergillosis presenting as pericarditis and cardiac tamponade

A 38-year-old leukemic patient developed pericarditis and cardiac tamponade due to Aspergillus niger one month after undergoing bone marrow transplantation. She failed to improve even though amphotericin B and rifampin therapy had been initiated before infection was evident. Her unique case illustrates both the unusual presentations of invasive aspergillosis and the difficulty of diagnosing and treating this increasingly common disease.

Aspergillus vegetative endocarditis and complete heart block in a patient with acute leukemia

Aspergillus flavus vegetative endocarditis together with myocardial abscesses and pneumonitis developed in a patient with acute lymphocytic leukemia. The initial diagnosis was not suspected until 67gallium imaging revealed a radiographically undetectable thoracic abnormality. Despite apparently "early" diagnosis, antifungal therapy was inadequate to prevent disruption of the bundle of His, complete heart block and death.