In vitro and in vivo effects of rifabutin alone or combined with atovaquone against Toxoplasma gondii.

The efficacy of rifabutin (RIFA) alone or in combination with atovaquone (ATO) was examined in vitro and in a murine model of acute toxoplasmosis. In vitro studies were performed with MRC5 fibroblast tissue cultures, with quantification of Toxoplasma growth by enzyme-linked immunosorbent assay. For in vivo studies, mice were acutely infected with 10(4) tachyzoites of the virulent RH strain and were then treated perorally for 10 days from day 1 or day 4 postinfection. The efficacy of each drug regimen was assessed by determination of survival rates and sequential titration of parasites in blood, brain, and lungs by a tissue culture method. In vitro, RIFA was inhibitory for Toxoplasma growth at concentrations between 0.5 and 20 micrograms/ml; the 50% inhibitory concentration was estimated to be 1.68 micrograms/ml. When RIFA and ATO were combined, synergistic effects were noted for RIFA at 20 micrograms/ml combined with ATO at 0.01 or 0.02 microgram/ml and RIFA at 1, 2, or 5 micrograms/ml combined with ATO at 0.02 microgram/ml. In vivo, administration of RIFA at 200 mg/kg of body weight per day from day 1 to day 10 resulted in a 100% protection during treatment, with clearance of parasites from the blood, brain, and lungs. After the cessation of therapy, relapses occurred in the brain and lungs; the mortality was 46% at the end of the experiment (day 30). Among the mice treated with RIFA at 200 mg/kg/day from day 4 to day 14, no death was recorded during the treatment period and a marked reduction in parasite burdens was observed in blood and tissues; however, relapses occurred and 10% of mice survived until day 30. Administration of RIFA at 200 mg/kg/day in combination with ATO at 100 mg/kg/day resulted in a marked prolongation of survival compared with that for mice that received ATO or RIFA alone. However, in mice receiving the combination, parasite burdens in blood and organs were similar to those in mice treated with RIFA alone. These results confirmed the activity of RIFA in the treatment of acute toxoplasmosis and the potential of the combination of RIFA-ATO since the two drugs act synergistically against Toxoplasma gondii.

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.

Activity of FCE 22891 compared with cefuroxime axetil and cefixime in pulmonary and subcutaneous infections in mice.

The therapeutic activity of FCE 22891 was compared with that of two new oral cephalosporins, cefuroxime axetil and cefixime against Streptococcus pneumoniae respiratory infection and subcutaneous abscesses induced by mixed aerobes and anaerobes in mice. In experimental pneumonia FCE 22891 was the most active antibiotic. In aerobic abscesses FCE 22891 proved the most active agent in infections induced by methicillin susceptible and resistant Staphylococcus aureus while all three compounds were very active, against Str. pyogenes. In abscesses caused by Gram-negative bacteria, FCE 22891 showed good and constant efficacy. Cefixime was the most active drug against the two susceptible strains of Escherichia coli and Enterobacter cloacae and also against resistant Esch. coli but was inactive against a strain of Ent. cloacae that produced cephalosporinase. Cefuroxime axetil was less active than the other two drugs against Gram-negative bacteria with adequate efficacy only against a susceptible strain of Ent. cloacae. FCE 22891 was more effective than cefixime and cefuroxime axetil in preventing and reducing the size of abscesses induced by Bacteroides fragilis 101. We conclude that FCE 22891, despite its short half life of 6 min in mice, exerts comparable and sometimes better activity than the two oral cephalosporins characterized by longer half lives.

Activity of FCE 22101 and other beta-lactam antibiotics against experimental genital infections in the rat and mouse.

The therapeutic activities of the parenterally administered penem FCE 22101, cefuroxime and ampicillin were compared in an experimental model of genital infections in progesterone-treated virgin rats and normal female mice. Treatment with FCE 22101 significantly inhibited the proliferation of Staphylococcus aureus ATCC 13709, Escherichia coli G and Enterobacter cloacae 1321 E, as compared with untreated controls. Against Staph. aureus ampicillin was slightly more active than cefuroxime, which showed equivalent activity to FCE 22101, while against Esch. coli and Ent. cloacae cefuroxime and ampicillin were less active than FCE 22101. The activity of the antibiotics against beta-lactamase-producing strains was also tested and here FCE 22101 exhibited the greatest inhibitory effect on bacterial growth.

Synthesis and antimicrobial spectrum of FCE 22101 and its orally available ester FCE 22891.

The most efficient routes for the synthesis of FCE 22101, a penem antibiotic characterized by a carbamoyloxymethyl sidechain at C-2 identical to that of cefuroxime and cefotaxime, and of FCE 22891, its orally absorbed pro-drug, are described. On the basis of in-vitro antimicrobial profile and other characteristics the compounds have been considered worthy of further development.

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.

Laboratory evaluation of a new long-acting 3-azinomethylrifamycin FCE 22250.

FCE 22250 (3-(N-piperidinomethylazino)methylrifamycin SV) is a member of the new class of 3-azinomethylrifamycins characterized by a long persistance in animals, a good oral absorption and a broad antibacterial spectrum including mycobacteria. In the experimental mice infection sustained by Mycobacterium tuberculosis H37Rv, FCE 22250 shows an efficacy 14 times higher than rifampicin and is still therapeutic when administered once every three weeks.

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.

Novel rifamycins. III. Synthesis and antibacterial activity of 3-amidino- and of 4-aminoimidazolo[4,5-c]rifamycin derivatives.

A number of semisynthetic rifamycin derivatives modified at position 3 and/or 4, belonging to general structures 2 and 4 (see Scheme 1), have been obtained. The synthesis and the biological activities of the new compounds are described. Compounds 4p and 4q display very good antimycobacterial activity in mice.