An investigation of the pharmacokinetics and autoinduction of rifabutin metabolism in mice treated with 10 mg/kg/day six times a week for 8 weeks.

Plasma, lung and spleen concentrations of rifabutin have been measured in mice after single and multiple oral administrations of the drug. Rifabutin concentrations in spleen were similar to those measured in plasma, whereas concentrations in lung were higher. No significant autoinduction of rifabutin metabolism was observed.

In-vitro and in-vivo activity of rifabutin against Toxoplasma gondii.

The activity of rifabutin against Toxoplasma gondii was investigated in vitro and in vivo. One set of in-vitro studies used either a low virulence or a high virulence T. gondii strain subcultured in drug-free conditions after exposure to various drug concentrations. No parasite growth was observed after subculture at 1 month after exposure to 6 mg/L of rifabutin for the low virulence and 12 mg/L for the high virulence strain. The IC50 of rifabutin was 26.5 mg/L in a different series of experiments using an enzyme-linked immunoassay) and the T. gondii high virulence strain. In similar experiments with clarithromycin, low virulence and high virulence parasites grew in drug-free subcultures following exposure to drug concentrations as high as 100 mg/L; the IC50 of clarithromycin exceeded 100 mg/L for the high virulence strain. In the acute toxoplasmosis murine model, mice received a 12 day treatment starting 5 days before infection with high virulence parasites. Survival was significantly improved compared with untreated controls in response to 50, 100 and 200 mg/kg/day rifabutin and 100 and 200 (but not 50) mg/kg/day clarithromycin, and with the combination of the two drugs at 25, 50 and 100 mg/kg/day. Survival was significantly improved when combination therapy was administered. The calculated ED50 values (mg/kg/day) were 160.5 for rifabutin, 119.4 for clarithromycin, and 114.8 for the combination. In the present experimental conditions rifabutin proved effective in vitro and in vivo against T. gondii and showed potentiation with clarithromycin in vivo.

Effectiveness of rifabutin alone or in combination with isoniazid in preventive therapy of mouse tuberculosis.

The ever-increasing incidence of tuberculosis calls for the implementation of control measures, including new efficient, short-term preventive therapies to replace 6 to 12 months of isoniazid therapy. The efficacies of 12-week regimens of rifabutin or isoniazid given daily and the combination of the two drugs administered intermittently were evaluated in mice infected with Mycobacterium tuberculosis after vaccination with the bacillus Calmette-Guérin (BCG) to imitate some features of the natural infection in humans with a low number of persisting bacteria. Rifabutin at 10 mg/kg of body weight per day was highly effective as early as the eighth week of treatment: all spleens were sterilized and the number of bacteria was drastically reduced in the lungs (mean +/- standard deviation log CFU, 0.2 +/- 0.3, compared with 5.9 +/- 0.6 for untreated controls). No bacilli were found in the spleens or lungs of any of the animals treated for 12 weeks. The combination of rifabutin at 10 mg/kg plus isoniazid at 25 mg/kg twice weekly was almost as effective as rifabutin daily: after 8 weeks of treatment only two of six mice harbored a small number of mycobacteria in their spleens and lungs; at week 12, all spleens were sterilized and a total of eight colonies were isolated from the lungs of two of six mice. Daily isoniazid and once-weekly rifabutin plus isoniazid therapies were less effective. Colonies randomly isolated from the spleens and lungs of mice from different experimental groups were also tested for their susceptibilities to the two drugs. The three surviving colonies from rifabutin-treated mice and all colonies from those administered rifabutin plus isoniazid remained fully susceptible to either drug. In contrast, 2 (18%) of the 11 colonies randomly selected from isoniazid-treated mice became resistant to isoniazid (MIC, > 2 micrograms/ml), although they were still susceptible to rifabutin. Three months of treatment with rifabutin, either daily alone or twice a week combined with isoniazid, proved to be a valid candidate for tuberculosis preventive therapy.

Synthesis and structure-activity relations in the class of 2-(pyridyl)penems.

The isosteric CH----N substitution in the class of 2-arylpenems results in improved antibacterial activity, with retention of the favorable characteristic of stability towards renal dehydropeptidase. High therapeutic efficacy was demonstrated in experimental mice septicemias with the 2-(3-pyridyl) derivative 2b and its orally absorbed acetoxymethyl ester prodrug 4n.

New mechanism for methicillin resistance in Staphylococcus aureus: clinical isolates that lack the PBP 2a gene and contain normal penicillin-binding proteins with modified penicillin-binding capacity.

Seventeen clinical isolates of Staphylococcus aureus (from the United States and Europe) selected for low (borderline)-level methicillin resistance (MIC of methicillin, 2 to 4 micrograms/ml; MIC of oxacillin, 0.5 to 8 micrograms/ml) were examined for their mechanisms of resistance. Five strains were typical of heterogeneous S. aureus: they gave positive reactions with a DNA probe specific for mec and contained a small fraction (10(-6] of highly resistant cells (MIC, greater than 100 micrograms/ml). The rest of the 12 strains were homogeneous with respect to their methicillin resistance: the MIC of methicillin for all cells was 2 to 4 micrograms/ml, and no cells for which MICs were 50 micrograms/ml or higher were detectable (less than 10(-9]. None of these strains reacted with the mec-specific DNA probe. One representative strain of each group was characterized in more detail. Strain CDC-1, prototype of heterogeneous methicillin-resistant S. aureus, contained penicillin-binding protein (PBP) 2a; its DNA could transform a methicillin-susceptible and novobiocin-resistant recipient to methicillin resistance with ca. 35% linkage to Novr. Introduction of the "factor X" determinant (K. Murakami and A. Tomasz, J. Bacteriol. 171:874-879, 1989) converted strain CDC-1 to high, homogeneous resistance. Strain CDC-6, prototype of the second group of isolates, showed completely homogeneous MICs of methicillin, oxacillin, and cefotaxime. The strain contained modified "normal" PBPs: PBPs 1 and 2 showed low drug reactivity (and/or cellular amounts), and PBP 4 was present in elevated amounts. No PBP 2a could be detected. DNA isolated from strain CDC-6 could transform the methicillin-susceptible and novobiocin-resistant strain to methicillin resistance in a multistep fashion, but this resistance showed no genetic linkage to the Nov marker. We suggest that staphylococci with borderline resistance may contain at least three different classes of mechanism: heterogeneous, methicillin-resistant S. aureus, PBPs of modified drug reactivities, and the previously reported hyperproduction of beta-lactamase (L.K. McDougal and C. Thornsberry, J. Clin Microbiol. 23:832-839, 1986).

FCE 22101 and FCE 22891: in-vitro antibacterial activity at concentrations simulating human plasma levels following intravenous, intramuscular and oral administration.

The plasma concentrations of FCE 22101 observed following slow intravenous infusions (1 and 4 h), intramuscular injection and after oral administration of the prodrug FCE 22891 were simulated in a glass chamber containing bacterial cultures. The bacteria used were Staphylococcus aureus ATCC 13709, Staph. aureus 2101 (methicillin-resistant), Streptococcus faecium ATCC 8043, Escherichia coli ATCC 12407, Enterobacter cloacae 1321E and Ent. cloacae P99 (cefazolin-resistant). Addition of FCE 22101 was found to result in a reduction in number of all bacterial strains except Str. faecium, with which only bacteriostasis was observed.

Lytic and bactericidal activity of FCE 22101.

We have examined the lytic and cidal activities of FCE 22101 against bacteria exhibiting genetic tolerance (pneumococcal mutants) and bacteria phenotypically tolerant to penicillin (Escherichia coli, deprived of an essential amino acid). The pneumococcal strains included lyt- mutants in which the autolysin gene was inactivated or deleted and clinical isolates with penicillin MIC greater than 1.0 mg/l. The killing activity of FCE 22101 was superior to that of penicillin for all strains. FCE 22101 was also capable of inducing considerable lysis in all the lyt- strains in spite of the virtually complete inhibition (or actual absence) of the major autolysin. FCE 22101 also possessed bacteriolytic and cidal activity against a lysine-starved E. coli auxotroph (5 log kill in 24 h by 10 x MIC). Assays of the binding of FCE 22101 to the pneumococcal penicillin binding proteins (PBPs) suggest that the superior performance of FCE 22101 may be related to a uniquely high affinity for bacterial targets specifically involved with the bactericidal activity of beta-lactam antibiotics.

Penicillin-binding protein families: evidence for the clonal nature of penicillin resistance in clinical isolates of pneumococci.

In view of the worldwide emergence of penicillin-resistant pneumococci among clinical isolates it was of importance to examine a large number of strains to test the uniformity of the resistance mechanism. Among 160 clinical isolates of pneumococci (minimum inhibitory concentration [MIC], 0.005-16 micrograms/mL), susceptible strains showed a common pattern of five penicillin-binding proteins (PBPs) with high penicillin affinities (PBP 3 greater than 1A greater than or equal to 2A greater than 1B greater than 2B). PBPs 1A, 2A, and 2B (but not PBP 3) each showed distinct stepwise decreases in penicillin affinities parallel with increasing levels of antibiotic resistance. The number and molecular sizes of PBPs became variable in strains with MIC values greater than 1.0 microgram/mL; among 39 strains with a MIC of greater than or equal to 1.0 microgram/mL, 11 distinct and stable PBP patterns could be identified. Using PBP profiles, serotypes, and antibiotic resistance patterns, as well as data on isolation dates and sites, we identified at least three groups of resistant strains that showed clear indication of clonal origin.

LM 427, a new spiropiperidylrifamycin: in vitro and in vivo studies.

The spiropiperidylrifamycin LM 427 (4-deoxo-3,4-[2-spiro-N-isobutyl-4-piperidyl]-(1H)-imidazo-(2,5-dihydro) rifamycin S) displays a broad spectrum of potent antibacterial activity in vitro. In vivo it is particularly effective in the therapy of experimental tubercular infections of mice. Three schedules of treatment were employed and the best results were obtained when intermittent administrations were used (ED50 of LM 427; 7 times lower than rifampicin). LM 427 is well distributed in tissues of mice and rats, with lung concentrations 10 to 20 times higher than plasma levels.