Takeo Murakawa

Bactericidal Activity of Cephalosporins in an In Vitro Model Simulating Serum Levels

The bactericidal activity of cefazolin, cephaloridine, and cephalothin in a simulated intramuscular study (500 mg) and a simulated intravenous drip infusion study (2 g/2 h) is reported. In both model systems, the bactericidal activity of cefazolin surpassed that of cephalothin, and there were certain differences between cefazolin and cephaloridine in the simulated intramuscular study when human serum was used as a medium. In a routine reference static system, the drug levels were constant at the simulated peak level of each cephalosporin by both routes. In this system the three cephalosporins were equal in activity. In a third experiment, the effect of drug concentrations and exposure time on bactericidal activity of the cephalosporins was studied. The bactericidal activity of cephaloridine was the strongest of the three drugs when exposure time was 2 h and drug concentration was less than four times the minimal inhibitory concentration. At concentrations above four times the minimum inhibitory concentration, all three cephalosporins were equal in activity when the exposure time was 2 h.

Pharmacokinetics of fosmidomycin, a new phosphonic acid antibiotic.

The pharmacokinetics of fosmidomycin was investigated in animals and humans after parenteral and oral dosing. In dogs the serum concentration was 54.8 microgram/ml at 0.25 h after an intravenous dose of 20 mg/kg, and the half-life was 1.14 h. Peak concentration was 41.4 microgram/ml after an intramuscular dose of 20 mg/kg and 16.6 microgram/ml after an oral dose of 40 mg/kg. In volunteers, the serum concentrations 0.25 h after dosing was 157 microgram/ml after an intravenous dose of 30 mg/kg, 12.3 microgram/ml after an intramuscular dose of 7.5 mg/kg, and 2.45 microgram/ml after an oral dose of 500 mg. More than 90% of the given dose was excreted in the 24-h urine in rats and dogs after parenteral dosing with 20 mg/kg. The 24-h urinary recovery was 45.8% of the given dose in rats after oral dosing with 100 mg/kg and 37.8% in dogs after oral dosing with 40 mg/kg. In volunteers 85.5% of the intravenous dose (30 mg/kg), 66.4% of the intramuscular dose (7.5 mg/kg), and 26.0% of the oral dose (500 mg) were excreted unchanged in the 24-h urine. In the multiple-dose study, there was no accumulation of fosmidomycin in the serum even after 21 consecutive intramuscular dosings of 1 g every 6 h or 29 consecutive 0.5-h drip infusions of 2 g every 6 h. Biliary excretion was extremely low in rats. Fosmidomycin was well distributed to the tissues of rats after parenteral and oral dosing. The lymph concentrations in dogs were nearly the same as serum concentrations. Serum protein binding was low (4% or less) to mouse, rat, dog, and human serum. Images

Pharmacokinetics of ceftizoxime in animals after parenteral dosing.

The pharmacokinetic profile of ceftizoxime was studied in mice, rats, dogs, and monkeys given the drug in a single parenteral dose. The serum data after an intravenous injection were analyzed by the two-compartment open model. Cefotiam, cefmetazole, cefotaxime, and cefamandole were used as reference drugs. High concentrations of ceftizoxime were attained in the sera of all test animals and in the tissues of rats after parenteral dosing. The serum concentrations of ceftizoxime were higher than those of the other antibiotics in large animals (dogs and monkeys), but were lower in small animals (mice and rats). About 80% of ceftizoxime was excreted unchanged in the 24-h urine of all species tested. The biliary excretion of ceftizoxime was low: 3.7% in rats and 0.59% in dogs. However, therapeutically significant concentrations of ceftizoxime were found in the bile of dogs. Ceftizoxime was stable in biological fluids such as serum, urine, and tissue homogenates, but cefotaxime was unstable in rat tissue homogenates. Binding of ceftizoxime to serum protein in all species was the lowest of all the antibiotics: 31% for humans, 17% for dogs, and 32% for rats.

New in vitro kinetic model for evaluating bactericidal efficacy of antibiotics.

A new in vitro model was devised for evaluating the bactericidal activity of antibiotics under dynamic conditions. This model accurately reproduced the observed serum levels of antibiotics after intravenous dosing. The apparatus consists of two vessels which correspond to the central and peripheral compartments of a two-compartment open model. The volume of medium in each vessel and flow rates of media were determined from the pharmacokinetic parameters calculated from the observed serum levels selected for simulation. The bactericidal activity of cefazolin against strains of Escherichia coli and Klebsiella pneumoniae showing different minimal inhibitory concentrations was investigated with the apparatus simulating serum levels after intravenous injection, and the bactericidal activity was evaluated with respect to the relationship between the minimal inhibitory concentration and the serum levels.

Exudate levels and bactericidal activity of cefazolin in a new local infection system using rat granuloma pouches.

An experimental local infection system has been developed in which exudates are induced with croton oil in granuloma pouches of rats. This system provided a suitable model for the evaluation of the therapeutic effect of two antibiotics, cefazolin and cephalothin. Exudate levels of cefazolin were found to be higher than those of cephalothin, and these levels correlated with the higher serum level of cefazolin. The therapeutic effect of cefazolin, after intramuscular injection of 20 mg of each antibiotic per kg, was superior to that of cephalothin in eradicating both Staphylococcus aureus and Escherichia coli.

In Vitro and In Vivo Evaluation of Ceftezole, a New Cephalosporin Derivative

Ceftezole, a new cephalosporin derivative, was compared with cefazolin, cephaloridine, and cephalothin. Data obtained indicate that it is a broad-spectrum antibiotic, with almost identical antimicrobial activity against pathogenic organisms isolated from patients. The therapeutic effect of ceftezole on experimental infections in mice was similar to that of cefazolin and was superior to that of cephalothin. The binding of ceftezole to serum proteins was somewhat less than that of cefazolin. The concentrations of ceftezole in the sera of test animals and human volunteers were determined after intramuscular injection of 20 mg/kg and after a single dose of 500 mg, respectively. The concentration of ceftezole in the serum of volunteers peaked at 24.9 μg/ml 15 min after injection and remained effective (about 2.6 μg/ml) at 4 h. The half-life in serum under the same conditions was 56 min, i.e., about one-half that of cefazolin. The 24-h urinary recovery rate was 87.5%. Most of the administered ceftezole was excreted unchanged mainly through the urinary tract. The biliary excretion rate in SD strain rats after intramuscular injection of 20 mg/kg was about 4.4%. As compared with commercially available cephalosporins, ceftezole was second only to cefazolin in biliary excretion rate. Various tissue levels of ceftezole in animals were higher than cephalothin but, with the exception of renal levels in the early stage after administration, were lower than cefazolin.

Effect of Ceftizoxime, a New Cephalosporin Antibiotic, on Binding of Bilirubin to Human Serum Albumin

An investigation and comparison of the competitive effect of ceftizoxime, a new cephalosporin, and other beta-lactam antibiotics on in vitro binding of bilirubin to human serum albumin showed that at a normal range of serum albumin (3.48 g/dl) and bilirubin (0.94 mg/dl) in healthy infants, free bilirubin did not increase in the presence of any of the test antibiotics at concentrations up to 640 micrograms/ml. When the albumin concentration was decreased to one-fifth of the normal human range, only ceftizoxime caused no bilirubin displacement.

Laboratory Evaluation of FR10024, a New Cephalosporin Derivative

FR10024 is a broad-spectrum antibiotic. The in vitro antibacterial activity of FR10024 against clinical isolates of Staphylococcus aureus, Escherichia coli, Klebsiella pneumoniae, and Proteus mirabilis is greater than that of any of the cephalosporins developed to date. Indole-positive Proteus, Enterobacter, and Citrobacter are resistant to FR10024, as is true for the other cephalosporins. However, more than half of the strains of Enterobacter and Citrobacter tested were susceptible to FR10024 at an inoculum of 106 cells/ml. A single subcutaneous injection of FR10024 to mice with peritoneal infections due to S. aureus and several species of gram-negative bacilli gave a protective effect inferior to that of cefazolin but appeared to be superior to that of cephalothin. When given in two divided doses, however, the protective effect of FR10024 was enhanced and almost equaled that of cefazolin. The serum levels and rates of urinary recovery of FR10024 varied in different animal species. The mean peak serum level of FR10024 in humans after a single intramuscular injection of 500 mg was two times higher than that of cephalothin. The serum half-life after intramuscular injections of 250 and 500 mg was slightly shorter than that of cephalothin. After receiving 250 mg of FR10024 intramuscularly the urinary recovery rate was 87.7% in healthy volunteers. The biliary excretion rate of FR10024 was particularly high. The 24-h excretion of FR10024 in rats was 63.3%, this being six to seven times higher than that for cefazolin, which has the highest biliary excretion of the other known cephalosporins. When FR10024 was injected intramuscularly (20 mg/kg), it was found that the hepatic levels of FR10024 in rats were the highest of all the cephalosporins, including cefazolin, but the levels of FR10024 in other tissues were not as high as those of cefazolin.

Characteristics of Biliary Excretion of Cefazolin and Other Cephalosporins with Reference to the Relationship between Serum Levels and Administration Conditions

The biliary excretion of cefazolin was compared with that of cephalothin and cephaloridine in rats and man. In rats, the biliary levels were dose-related with cefazolin and cephalothin but not with cephaloridine. Biliary levels were higher than serum levels after injection of 10--80 mg/kg of cefazolin and cephalothin, whereas serum levels of cephaloridine after injection were higher than biliary levels. The highest biliary levels of cefazolin were obtained by intravenous injection, followed by intramuscular injection and drip infusion. In man, a crossover study was made to compare biliary levels of cefazolin with those of cephaloridine and cephalothin. After a single 1-gram intravenous injection, the peak levels of cefazolin ranged from 0.85 to 21 mug/ml and those of cephaloridine varied from 0.55 to 3.9 mug/ml. After a 3-gram intravenous injection, the peak biliary levels of cefazolin ranged from 35.5 to 270 mug/ml and those of cephalothin from 0.3 to 64 mug/ml. The chemotherapeutic biliary levels of cefazolin able to inhibit susceptible organisms were obtained by 3-gram intravenous injections.

Enterohepatic Circulation of a New Oral Cephalosporin, FR10612, and Its Effect on Serum and Tissue Levels in Rats

Serum levels of FR10612 given orally to rats persisted significantly longer than did those of cephalexin. Since the elucidation of this phenomenon observed in rats is considered to be pertinent to the understanding of the drug kinetics of FR10612 in other animals including man, the present study was undertaken. From the dose-response curve of the serum levels of FR10612 in rats, it is apparent that the maximum oral absorption is obtained in the range of 100-400 mg/kg. Even when the doses were increased from 100 to 1,000 mg/kg, the tissue levels with the exception of the kidneys, did not increase significantly. However, the persistence of the tissue levels was enhanced. The serum and tissue levels of FR10612 in rats after repeated massive dosings did not increase accumulatively. From the experimental results of FR10612 in rats with ligated bile ducts and the results obtained after intravenous injection, it seems clear that the prolonged in vivo levels of FR10612 in rats after oral dosing are closely related to its enterohepatic circulation.