Yoshiyuki Takase

In vitro antibacterial properties of AT-2266, a new pyridonecarboxylic acid.

AT-2266, 1-ethyl-6-fluoro-1,4-dihydro-4-oxo-7-(1-piperazinyl)-1,8-naphthyridine-3 -carboxylic acid, is a new pyridonecarboxylic acid derivative with broad and potent antibacterial activity. It inhibited some gram-positive bacteria, such as staphylococci and Bacillus subtilis, and most gram-negative bacteria, including Serratia marcescens, Pseudomonas aeruginosa, Haemophilus influenzae, and Campylobacter jejuni, at concentrations of 0.1 to 0.78 microgram/ml, and most gram-positive bacteria, glucose-nonfermenters, and Mycoplasma pneumoniae at concentrations of 1.56 to 12.5 micrograms/ml. Most of the clinical isolates tested were as susceptible to AT-2266 as were laboratory strains. The antibacterial potency of AT-2266 was higher than those of pipemidic acid and nalidixic acid and similar to that of norfloxacin. AT-2266 was not cross-resistant with antibiotics and inhibited most highly nalidixic acid-resistant bacteria at concentrations of 1.56 to 3.13 micrograms/ml. Its activity was barely affected by the addition of horse serum or sodium cholate but weakened by lowering the medium pH or increasing the inoculum size. AT-2266 was bactericidal at concentrations near its minimal inhibitory concentrations. Frequencies of mutants resistant to 10 micrograms of AT-2266 per ml were lower than 4.0 x 10(-9).

Pipemidic Acid, a New Antibacterial Agent Active Against Pseudomonas aeruginosa: In Vitro Properties

Pipemidic acid, 8-ethyl-5,8-dihydro-5-oxo-2-(1-piperazinyl)-pyrido [2,3-d]pyrimidine-6-carboxylic acid, is a new derivative of piromidic acid. It is active against gram-negative bacteria including Pseudomonas aeruginosa as well as some gram-positive bacteria. Its potency is generally greater than that of piromidic acid and nalidixic acid. Cross-resistance is not observed between pipemidic acid and various antibiotics, and most of bacteria resistant to piromidic acid and nalidixic acid are moderately susceptible to pipemidic acid. The activity of pipemidic acid is scarcely affected by the addition of serum, sodium cholate, or change of medium pH, but is subject to the influence of inoculum size. Its action is bactericidal above minimal inhibitory concentrations.

Pharmacokinetics of AT-2266 Administered Orally to Mice, Rats, Dogs, and Monkeys

The pharmacokinetics of AT-2266 (1-ethyl-6-fluoro-1,4-dihydro-4-oxo-7-(1-piperazinyl)-1,8-naphthyridine- 3-carboxylic acid) were studied in various experimental animals and compared in a number of aspects with those of norfloxacin. Both agents were administered orally. The mean peak plasma levels of AT-2266 in mice, rats, and dogs (given a single dose of 50 mg/kg for mice and rats and 25 mg/kg for dogs) were 2.39, 1.63, and 5.00 μg/ml, respectively, with elimination half-lives of 2.24, 2.81, and 5.76 h. The respective mean plasma levels of norfloxacin at similar dosages were 0.510, 0.410, and 0.700 μg/ml; elimination half-lives were 1.40, 2.35, and 6.06 h. In dogs repeatedly dosed with 25 mg of AT-2266 per kg every 12 h, the mean peak plasma levels after the third and fifth doses were about 1.4 times those after the first dose. The binding rates of AT-2266 and norfloxacin to plasma of mice, rats, and dogs and to human serum ranged from 27.6 to 40.2% and 39.8 to 44.2%, respectively. In rats receiving a single dose of 50 mg/kg, the respective mean peak levels of AT-2266 in plasma, lung, muscle, and kidney were 2.47, 4.60, 5.35, and 33.9 μg/ml or g, whereas those of norfloxacin were 0.234, 0.390, 0.272, and 2.05 μg/ml or g. AT-2266 was widely distributed in tissues of dogs and monkeys after repeated dosage. The respective 24-h recoveries of AT-2266 from urine of mice, rats, and dogs after single doses of 50, 50, and 25 mg/kg were 56.6, 40.5, and 64.1%, and recoveries of norfloxacin at these doses were 4.40, 2.91, and 5.34%. The respective 24-h recoveries of AT-2266 from bile and feces of rats given a single dose of 50 mg/kg were 2.47 and 52.7%. Bioautography of plasma and urine indicated that AT-2266 was metabolized to but a slight degree. The results indicate that AT-2266 is better than norfloxacin in oral absorption and similar to the latter in stability to metabolic inactivation. Images

Pipemidic Acid: Absorption, Distribution, and Excretion

Pipemidic acid was absorbed well by the oral route. Its peak levels in plasma ranged from 4 to 12 μg/ml at an oral dose of about 50 mg/kg in mice, rats, dogs, monkeys, and men. The protein binding of pipemidic acid was about 20% in dog plasma and about 30% in human serum. Pipemidic acid was distributed to most of the organs and tissues tested at the concentrations comparable to or higher than the plasma level. Its concentrations in bile and urine were much higher than the plasma level. About 25 to 88% of orally administered pipemidic acid was excreted into urine in a bacteriologically active form, the percentage depending on the animals and doses employed. The remainder was excreted into feces in men. The main active principle in vivo was unchanged pipemidic acid itself. The mean lethal dose of pipemidic acid after a single oral dose was more than 16,000 mg/kg in mice. No abnormalities were observed in mice orally receiving pipemidic acid once a day for 4 weeks at doses of 1,000, 2,000, and 4,000 mg/kg per day, and in rats orally receiving the drug once a day for 2 weeks at doses of 400 and 1,600 mg/kg per day.

Activity of AT-2266 compared with those of norfloxacin, pipemidic acid, nalidixic acid, and gentamicin against various experimental infections in mice.

AT-2266 (1-ethyl-6-fluoro-1,4-dihydro-4-oxo-7-(1-piperazinyl)-1, 8-naphthyridine-3-carboxylic acid) showed marked activity in vivo when administered orally to mice bearing systemic, pulmonary, dermal, or urinary tract infections due to variety of organisms. The activity of AT-2266 was uniformly higher than those of norfloxacin, pipemidic acid, and nalidixic acid against all of the infections. The activity of AT-2266 administered orally was almost comparable to that of gentamicin administered subcutaneously against urinary tract infections due to gram-negative organisms but was generally lower against other infections. AT-2266 exhibited significant activity against infections due to gentamicin-resistant and nalidixic acid-resistant organisms.

Pipemidic Acid: Its Activities Against Various Experimental Infections

Pipemidic acid, a structural relative of piromidic and nalidixic acids, exhibited substantial therapeutic activity when it was administered orally to mice bearing either widely disseminated or relatively localized infections with Staphylococcus aureus and a variety of gram-negative bacilli. The activity of pipemidic acid was always greater than that of piromidic and nalidixic acids; in infections with Pseudomonas aeruginosa and in bacilli resistant to the latter two drugs, pipemidic acid exhibited significant activity. In limited comparative studies, the activities of pipemidic acid were generally superior to the activities of cephalexin, ampicillin, and carbenicillin. Gentamicin, administered subcutaneously, was more active than pipemidic acid, given either orally or subcutaneously, against both systemic and localized infections with P. aeruginosa. The therapeutic accomplishments of pipemidic acid were attained with well-tolerated doses.