Eugene L. Moss

In vitro and in vivo activities of SCH 56592 (Posaconazole), a new triazole antifungal agent, against Aspergillus and Candida

ABSTRACT SCH 56592 (posaconazole), a new triazole antifungal agent, was tested in vitro, and its activity was compared to that of itraconazole against 39 Aspergillus strains and to that of fluconazole against 275 Candida and 9 Cryptococcus strains. The SCH 56592 MICs for Aspergillus ranged from ≤0.002 to 0.5 μg/ml, and those of itraconazole ranged from ≤0.008 to 1 μg/ml. The SCH 56592 MICs for Candida andCryptococcus strains ranged from ≤0.004 to 16 μg/ml, and those of fluconazole ranged from ≤0.062 to >64 μg/ml. SCH 56592 showed excellent activity against Aspergillus fumigatus andAspergillus flavus in a pulmonary mouse infection model. When administered therapeutically, the 50% protective doses (PD50s) of SCH 56592 ranged from 3.6 to 29.9 mg/kg of body weight, while the PD50s of SCH 56592 administered prophylactically ranged from 0.9 to 9.0 mg/kg; itraconazole administered prophylactically was ineffective (PD50s, >75 mg/kg). SCH 56592 was also very efficacious against fluconazole-susceptible, -susceptible dose-dependent, or -resistantCandida albicans strains in immunocompetent or immunocompromised mouse models of systemic infection. The PD50s of SCH 56592 administered therapeutically ranged from 0.04 to 15.6 mg/kg, while the PD50s of SCH 56592 administered prophylactically ranged from 1.5 to 19.4 mg/kg. SCH 56592 has excellent potential for therapy against seriousAspergillus or Candida infections.

Comparative Activity of Sisomicin, Gentamicin, Kanamycin, and Tobramycin

Gentamicin, sisomicin, tobramycin, and kanamycin were compared in parallel tests in vitro and in vivo against a variety of bacterial strains and species. A number of differences were seen in vitro, in particular: (i) the lower activity of kanamycin, (ii) the greater activity of tobramycin against Pseudomonas, (iii) the greater activity of gentamicin and sisomicin against Serratia, and (iv) the generally similar results with tobramycin, gentamicin, and sisomicin against species other than Pseudomonas and Serratia, with the ranking in order of decreasing activity being sisomicin, gentamicin, and tobramycin. Analysis of disc test results suggested that the gentamicin disc is not adequate for testing the susceptibility of all bacteria to sisomicin or tobramycin. In vivo tests did not confirm all specifics of in vitro tests; results of in vivo tests indicated that sisomicin may be the most active. It is suggested that the place of each of the antibiotics in human therapy can best be evaluated by more rigorous in vivo tests and clinical studies rather than extensive in vitro comparisons.

In vitro and in vivo activities of SCH 42427, the active enantiomer of the antifungal agent SCH 39304.

SCH 39304, a new triazole antifungal agent, is a 50:50 racemic mixture of two enantiomers, SCH 42427 and SCH 42426. The activities of these three compounds were compared in a series of in vitro and in vivo experiments. SCH 42427 was twofold more active in vitro against a variety of yeasts and dermatophytes than SCH 39304, while SCH 42426 was inactive (MICs greater than 64 micrograms/ml). In a systemic Candida albicans infection in mice, SCH 42427 administered orally (p.o.) (50% protective dose [PD50], 0.17 mg/kg of body weight; 50% effective dose, [ED50], 0.47 mg/kg) had greater efficacy than SCH 39304 (PD50, 0.21 mg/kg; ED50, 0.62 mg/kg) and SCH 42426 (greater than 100 mg/kg for PD50 and ED50). In a pulmonary Aspergillus flavus infection in mice, SCH 42427 p.o. (PD50, 13 mg/kg) was also more effective than SCH 39304 (18 mg/kg) and SCH 42426 (greater than 250 mg/kg). In a C. albicans vaginal infection in hamsters, SCH 42427 p.o. (ED50, 3.5 mg/kg) was more active than SCH 39304 (8.5 mg/kg) and SCH 42426 (320 mg/kg). Following topical administration, against a Trichophyton mentagrophytes infection in guinea pigs, SCH 42427 was about 2-fold more active than SCH 39304 and about 100-fold more active than SCH 42426. These and other results indicated that SCH 42427 is the active enantiomer, responsible for all the antifungal activity observed with SCH 39304.

Selective chemical modifications of polymyxin B

Polymyxin B (1) monohydrochloride was converted to the tetra-BOC derivatives 1b and 1c by reaction with di-tert-butyl dicarbonate. The structures of these protected intermediates were established utilizing a degradative sequence that afforded 3 and 5. A method for the deprotection 2,4-dinitrophenylamines to the free amine, utilizing a strongly basic ion-exchange resin, was developed for use in the degradative sequence. The tetra-BOC derivatives 1b and 1c were used to prepare several Polymyxin B derivatives 6-27 at the DAB1 and DAB9-gamma-amine. The antibacterial activity of these selectively functionalized derivatives is reported here.

Chemotherapeutic Evaluation of 5-Episisomicin (Sch 22591), a New Semisynthetic Aminoglycoside

5-episisomicin (Sch 22591) is a novel semisynthetic aminoglycoside with a spectrum and potency similar to gentamicin in its activity against susceptible bacterial strains, but with increased potency against Pseudomonas, Providencia, and Proteus rettgeri. It is also more active than tobramycin and amikacin against these last-mentioned species. Against resistant strains, Sch 22591 is significantly more active than gentamicin or tobramycin. Against resistant gram-negative bacteria other than Pseudomonas, Sch 22591 has activity similar to that of amikacin, but Sch 22591 is more potent. Against Pseudomonas strains, it is active against most gentamicin- and tobramycin-resistant strains and is more active than the other three antibiotics. Some Pseudomonas strains are resistant to Sch 22591, but susceptible to amikacin. Against a selection of aminoglycoside-resistant staphylococci, Sch 22591 has very good activity against strains resistant to tobramycin, amikacin, and gentamicin. The superior in vitro potency of Sch 22591 against Pseudomonas has been confirmed in vivo in experimental infections in mice. Absorption in dogs is similar to that of other aminoglycoside antibiotics. The acute toxicity of Sch 22591 in mice is greater than that of gentamicin; its vestibular toxicity potential and nephrotoxicity potential in cats and rats appear to be similar to those of gentamicin.

Biological Activity of Antibiotic G-418, a New Micromonospora-Produced Aminoglycoside with Activity Against Protozoa and Helminths

On the basis of parallel in vitro studies with antibiotic G-418, gentamicin, neomycin, and kanamycin, antibiotic G-418 was found to be less potent than gentamicin but more active than either kanamycin or neomycin against most strains, with the exception of Pseudomonas, for which neomycin was more active than antibiotic G-418, and enterococci, for which antibiotic G-418 was more active than the other three antibiotics. Mouse protection tests indicated that antibiotic G-418 is approximately half as potent as gentamicin and its acute toxicity is one-half to one-third that of gentamicin.

Comparison of SCH 39304, fluconazole, and ketoconazole for treatment of systemic infections in mice.

SCH 39304 was compared with fluconazole and ketoconazole in a systemic Candida albicans infection in mice (10(6) CFU per mouse). Results were based on survival rates and CFU in kidneys following once-daily oral treatment of 2, 5, or 10 days duration. In normal mice, SCH 39304 (dose to reduce kidney counts by 4 log units, 0.5 mg/kg of body weight) was 3 and 200 times more active than fluconazole and ketoconazole, respectively. In immunocompromised mice (gamma irradiation, 600 rads), SCH 39304 (dose to reduce kidney counts by 4 log units, 1.3 mg/kg) was 35 and greater than 100 times more active than fluconazole and ketoconazole, respectively. In normal mice, when the infecting inoculum varied from 10(5) to 10(7) CFU, only a fivefold increase in the dose to reduce kidney counts by 4 log units was observed with SCH 39304. Excellent protection was also seen when mice were treated with a single oral dose of SCH 39304 up to 24 h prior to infection with C. albicans. Studies in a systemic C. albicans infection model indicated that SCH 39304 is equally efficacious following either oral or intravenous administration. In a systemic Aspergillus flavus infection, mice treated with SCH 39304 (5 mg/kg) survived twice as long (16 days) as those treated with fluconazole (50 mg/kg) or controls did.

Biological Activity of Sch 14342, an Aminoglycoside Antibiotic Coproduced in the Gentamicin Fermentation

Sch 14342 is an aminoglycoside antibiotic coproduced as a minor component in the gentamicin fermentation. Sch 14342 was found to have the same antibacterial spectrum as gentamicin in vitro and in vivo, and was approximately one-third as active in mouse protection tests. Sch 14342 relative to gentamicin was one-third as toxic in acute tests in mice, one-eighth as toxic in renal toxicity tests in dogs, and an estimated one-tenth as toxic in cat ataxia tests. Sch 14342 possesses a significantly improved therapeutic index relative to gentamicin with reference to ataxia potential and renal toxicity.