Gerald E. Wagner

In Vitro Studies with Combinations of 5-Fluorocytosine and Amphotericin B

Synergistic antifungal activity of 5-fluorocytosine (5-FC) and amphotericin B was studied using an abbreviated checkerboard titration scheme. 5-FC was titrated in twofold increments (100 to 0.05 μg/ml) in the absence and presence of graded increments of amphotericin B (1.0. 0.5, 0.1, 0.05, and 0.01 μg/ml) in buffered yeast nitrogen base. A limited number of experiments were performed using expanded dual titration checkerboard schemes and growth curve studies. Forty-eight isolates of yeastlike organisms were tested; two were inhibited by the buffer system. Evidence of synergy, as indicated by a fourfold or greater reduction of the minimal inhibitory concentration of 5-FC in the presence of subinhibitory concentrations of amphotericin B, was seen with 11 of 46 isolates, or 24%, at the fungistatic level and with three isolates, or 7% at the fungicidal level. Indifferent results were obtained for 44 and 74% of the isolates, respectively, at the fungistatic and fungicidal levels. Antagonism was observed with three isolates.

In Vitro Activities of Five Oral Cephalosporins Against Aerobic Pathogenic Bacteria

Cefaclor (Lilly 99638) and cefatrizine (BL-S640, SK&F 70771) are orally absorbed, broad-spectrum semisynthetic cephalosporins. They were compared in vitro with cephalexin, cephaloglycin, and cepharadine against a variety of aerobic pathogenic bacteria by an agar dilution procedure. Cefaclor and cefatrizine were found to be similar or superior to cephalexin, cephaloglycin, and cephradine in terms of activity against gram-positive cocci other than enterococci. Only cefatrizine demonstrated any potentially useful activity against some susceptible isolates of enterococci. Cefaclor and cefatrizine also were highly active, equally or more so than the other oral cephalosporins, against several gram-negative species including Escherichia coli, Enterobacter aerogenes, and Klebsiella pneumoniae. None of the cephalosporins were particularly active against Enterobacter cloacae. Both cefaclor and cefatrizine were active against Proteus mirabilis; cefatrizine was uniquely active against indolepositive Proteus species.

In vitro and in vivo studies with BL-S786, cefoxitin, and cefamandole.

The in vitro antimicrobial activities of BL-S786, cefoxitin, and cefamandole against 90 isolates of Enterobacteriaceae, including Escherichia coli, Klebsiella pneumoniae, Proteus mirabilis, Enterobacter cloacae and E. aerogenes, were studied by using an agar dilution procedure. Comparison of geometric mean minimal inhibitory concentrations showed that BL-S786 was half as active as cefamandole against Enterobacter species, 2 to 4 times more active than cefamandole against all other species, and 4 to 25 times more active than cefoxitin against all species. In vivo experiments employed acute protection tests in infected mice, using five isolates each of the five genera. Drugs were administered intramuscularly in two doses 3 h apart at dosages of 2.5, 5, 10, 20, and 40 mg per mouse. In most instances, BL-S786 was the most efficacious drug, being some 1.3 to 9.1 times more active than cefoxitin in all experiments and 1.5 to 8.7 times more active than cefamandole in most experiments. BL-S786 and cefamandole were comparable in activity in experiments with E. aerogenes, whereas BL-S786 was superior in experiments with E. cloacae.

In vitro comparison of the antifungal activities of R34,000, miconazole and amphotericin B.

In vitro susceptibilities of 78 isolates of pathogenic filamentous fungi to the imidazole compounds R34,000 and miconazole and to amphotericin B were determined using an agar dilution technique. Allescheria boydii, Sporothrix schenckii and the dematiaceous fungi (Cladosporium, Fonsecaea and Phialophora spp.) were most susceptible to miconazole with minimum inhibitory concentration (MIC) values ranging from less than or equal to 0.25 to 32 microgram/ml and with geometric mean MIC (G-MIC) values of 0.56-1.24 microgram/ml. Isolates of Aspergillus fumigatus were more susceptible to amphotericin B and miconazole than to R34,000 with G-MIC values of 1.20 and 3.48 microgram/ml, respectively. Coccidioides immitis, Histoplasma capsulatum and Blastomyces dermatitidis were highly susceptible to all three drugs (G-MICs greater than 1 microgram/ml); R34,000 was the most active of the three compounds against C. immitis (G-MIC = 0.44 microgram/ml).

New Method for Susceptibility Testing with Antifungal Agents

A new method for the determination of minimal inhibitory and fungicidal concentrations of antifungal agents for filamentous fungi is described. 5-Fluorocytosine (5-FC) was used as a representative agent and was tested against the following genera: Allescheria, Aspergillus, Cladosporium, Fonsecaea, and Phialophora. 5-FC was found to be inhibitory but not fungicidal for many of the fungi tested, including eight of clinical origin. Images

Studies on the Mode of Action of 5-Fluorocytosine in Aspergillus Species

The mode of action of 5-fluorocytosine (5-FC) was studied in three isolates of pathogenic Aspergillus with varying degrees of susceptibility to the drug. Distribution studies showed that susceptibility or resistance to 5-FC was not dependent on uptake of the drug. While only a small percentage of the total 5-FC taken up was found in the RNA fraction of the cells, most remained in the acid-soluble intracellular pool. 5-FC, 5-fluorouracil (5-FU) and 5-fluorodeoxyuridine monophosphate (5-Fd-UMP) were among metabolites identified in the pool. In addition, fluoroorotic acid appeared to be a major constituent of the metabolites derived from 5-FC. The aspergilli also were capable of utilizing cytosine as a nitrogen source and this is suggested as a possible mechanism of resistance. A dual mode of action for 5-FC in the aspergilli is proposed. This consists of, first, incorporation of 5-FU into RNA and, second, inhibition of DNA synthesis by production of 5-FdUMP.

In vitro studies with ambruticin, a new antifungal antibiotic.

The in vitro antifungal inhibitory activities of ambruticin and of various antifungal drugs of choice against 190 fungal pathogens representative of the major human mycoses were compared using a modification of the ICS agar dilution technique. Ambruticin compared favorably with amphotericin B and miconazole when tested against the dimorphic pathogens Coccidioides immitis, Histoplasma capsulatum, and Blastomyces dermatitidis and against Aspergillus fumigatus. Miconazole was the most active compound against Sporothrix schenckii, Allescheria (Petriellidium) boydii, and selected dematiaceous fungi, with ambruticin giving minimal inhibitory, concentrations from 3- to 74-fold higher. Ambruticin compared unfavorably with amphotericin B and 5-fluorocytosine when tested against Candida and Torulopsis species. Ambruticin was not as active in vitro as tolnaftate when tested against the three genera of dermatophytic fungi, but compared favorably with miconazole.

Effects of Purines and Pyrimidines on the Fungistatic Activity of 5-Fluorocytosine in Aspergillus Species

The ability of some exogenously supplied purines, pyrimidines, and their nucleosides to antagonize the in vitro fungistatic activity of 5-fluorocytosine (5-FC) in Aspergillus species was examined. All compounds tested except thymidine were capable of altering the minimal inhibitory concentration of 5-FC for seven strains of aspergilli tested. In most instances, there was a reciprocal correlation between the ability of a compound to antagonize the fungistatic activity of 5-FC and the quantity of 5-FC taken up by cells in the presence of the compound over a 72-h period.

In Vitro Studies with Cephanone

A new parenteral cephalosporin, cephanone, was studied in vitro.

Chapter 13. Antifungal Agents

Publisher Summary This chapter discusses essential aspects of the history, pathological diagnosis and physiology, mycological aspects, host response, serology, treatment, clinical manifestation, and laboratory diagnosis of human aspergillosis, and the more recent topic of aflatoxins. The superinfections most commonly seen in illicit drug users are discussed followed by commonly seen fungal infections such as candidiasis and aspergillosis. The role of the radiologist in the diagnosis of opportunistic pulmonary fungal infections and their symptoms are discussed. The chapter also discusses specific fungal infections that include phycomycosis, aspergillosis, and nocardiosis. Chronic mucocutaneous candidiasis in immunosuppressed patients and patients with genetically determined diseases is reviewed; treatment with immunoreconstitution, 5-FC, clotrimazole or amphotericin B is discussed. The combination of immunoreconstitution, drug therapy, the importance of iron deficiency and other nutritional factors are also discussed followed by a review of clinical aspects of the mycotoxicoses in man and animals.