5-Fluorocytosine in human cryptococcosis

Because there are few persuasive data for selecting one semisynthetic penicillin or cephalosporin over another for treatment of serious staphylococcal infections, 118 recent clinical isolates of Staphylococcus aureus were studied to determine to what extent the presence of β-lactamase affected the relative anti-staphylococcal activity of six penicillins and seven cephalosporins. In addition, the effect of inoculum was studied for its possible effect on the anti-staphylococcal activity of the 13 β-lactam antibiotics. By all criteria, methicillin and nafcillin were clearly more resistant to both the inoculum effect and the production of staphylococcal β-lactamase, whereas benzylpenicillin and cephaloridine (especially benzyl-penicillin) were the most susceptible to these effects. Cephazolin was clearly more susceptible to staphylococcal β-lactamase and heavy inocula than the other cephalosporins (with the exception of cephaloridine), whereas cephalothin was the most resistant cephalosporin to these factors. The minimal inhibitory concentration for benzylpenicillin for tests with undiluted inoculum, compared to results with inoculum diluted 10⁻⁴, differed by a factor up to 16,384, whereas with methicillin and nafcillin the differences were rarely more than twofold. Ratios for the other 10 antibiotics fell between these extremes. These results suggest that methicillin or nafcillin is most stable to staphylococcal β-lactamase, and that benzylpenicillin and cephaloridine are the most susceptible.

Clinical and laboratory studies of a new micronized preparation of hamycin in systemic mycoses in man

The use of serum rather than broth as the diluent in the serum bactericidal test results in a significant decrease in the test level among patients receiving highly protein-bound semisynthetic penicillins.

In Vivo Susceptibility of Cryptococcus neoformans to Hamycin, Amphotericin B, and 5-Fluorocytosine

Previous investigations have shown that hamycin is 5 to 10 times more active in vitro than amphotericin B against Cryptococcus neoformans , whereas 5-fluorocytosine is approximately 15 times less active. Present studies are concerned with a comparison of these drugs in vivo. Three strains of C. neoformans which varied in both their virulence for mice and their susceptibilities to the antifungal agents were studied. Acute experimental infections were established in mice by using inocula containing approximately 4 × 10 6 cells. The mice were treated by gastric intubation for 28 days; daily dosages of the three drugs ranged from 12.5 to 250 mg/kg. The polyenes were suspended in 5% dimethyl sulfoxide, whereas 5-fluorocytosine was suspended in saline. Amphotericin B was the most effective drug, with almost complete absence of toxic deaths in control mice and increased survival in mice infected with two of the three strains and treated with 25 mg/kg per day or more. 5-Fluorocytosine was nontoxic but provided protection against only one strain. Hamycin was both the least effective and the most toxic compound, providing only slight protection at doses of 12.5 or 25 mg/kg per day and causing toxic deaths in over 50% of uninfected mice at doses above 25 mg/kg per day.

Cryptococcus neoformans and cryptococcosis

Images

In vitro and in vivo activity of hamycin against Blastomyces dermatitidis

Clinical responses of patients with blastomycosis to treatment with hamycin have been variable. An explanation for this was sought in a series of studies in which in vitro and in vivo susceptibilities to hamycin of five strains of Blastomyces dermatitidis were compared. Minimal inhibitory concentrations of hamycin for the five strains indicated uniformly high levels of in vitro susceptibility (0.008 to 0.016 mug/ml). In vivo activity was measured in infected mice treated intraperitoneally for a period of 28 days with doses of the drug ranging from 0.001 to 0.030 mg per mouse. Significant differences in response to treatment among the five strains were noted (P < 0.001), and protective doses were found to vary from 0.001 to >0.030 mg per mouse per day. Further observations of infected mice after treatment revealed marked rates of relapsing infection, and several strains caused death. Persistent inapparent infections were also detected on culture of selected organs. Toxicity due to hamycin alone was not observed. These results suggest that variations in clinical responses to hamycin therapy in treatment of blastomycosis reflect differences in pathogenesis and host response in vivo to the infecting organism rather than differences in susceptibility of B. dermatitidis to hamycin.