Masanao Shimizu

Relationships Between Plasma Concentrations of Diphenylhydantoin, Phenobarbital, Carbamazepine, and 3‐Sulfamoylmethyl‐1,2‐Benzisoxazole (AD‐810), a New Anticonvulsant Agent, and Their Anticonvulsant or Neurotoxic Effects in Experimental Animals

Summary: The relationships between plasma concentrations of diphenylhydantoin (DPH), phenobarbital (PB), carbamazepine (CBZ), and 3‐sulfamoylmethyl‐l,2‐benzisoxazole (AD‐810), a new anticonvulsant agent, and their anticonvulsant and neurotoxic effects were studied in various species of animals. Anticonvulsant activities of test drugs were examined by the maximal electroshock seizure (MES) test. Neurotoxicities were détérmined by the rotorod performance test in mice and rats and by behavioral observations in rabbits, dogs, and monkeys. It was demonstrated that both the anticonvulsant effects and the neurotoxic effects of the drugs tested were more closely correlated with their plasma concentrations than with the dosages administered. There was a critical plasma concentration for each drug to show an anticonvulsant effect or to cause a neurotoxic effect in an individual animal. The critical plasma concentrations for anticonvulsant and neurotoxic effects of each drug were relatively constant among different species, with the exception of DPH in rabbits, which had twice the value in other species. The therapeutic ranges of plasma concentrations of DPH, PB, and CBZ détérmined in various species of animals coincided well with those recommended clinically. AD‐810 was found to be effective against MES without signs of neurological toxicity in the ranges of plasma concentrations of 9.8 to 74.0, 10.8 to 95.0, 9.6 to 117.0, and 12.6 to 96.2 μg/ml in mice, rats, rabbits, and dogs, respectively. These results seem to suggest that AD‐810 may be effective clinically at plasma concentrations above 10 μg/ml, with a therapeutic range up to 70 μg/ml, which is much wider than the therapeutic ranges of DPH (10–20 μg/ml), PB (10–30 μg/ml), and CBZ (4–10 μg/ml).

Biochemical changes in unilateral brain injury in the rat: A possible role of free fatty acid accumulation

Cerebral energy metabolism was investigated in rats with the unilateral brain injury produced by the combination of left carotid artery ligation and systemic exposure to hypoxia. ATP and phosphocreatine levels in the left hemisphere were progressively reduced after the hypoxic-ischemic insult. The reduction of high-energy phosphate levels was accompained by an increase in sodium content and a decrease in potassium content. Mitochondria isolated from the damaged hemisphere showed a defect in ATP formation and oxygen uptake with a reduced ATP/O ratio. A large amount of free fatty acids (palmitic, stearic, oleic and arachidonic acids) accumulated in the injured hemisphere. The addition of unsaturated fatty acids (including oleic and arachidonic acids) to mitochondrial preparations caused an impairment of oxidative phosphorylation similar to that observed in mitochodria isolated from the damaged hemisphere.

Pharmacokinetics of a novel quinolone, AT-4140, in animals.

The pharmacokinetics of 5-amino-1-cyclopropyl-6,8-difluoro-1,4-dihydro-7-(cis-3,5-dimethyl-1- piperazinyl)-4-oxoquinoline-3-carboxylic acid (AT-4140) in experimental animals given a single oral dose of 5 mg/kg were studied. The mean peak levels of AT-4140 in plasma of mice, rats, dogs, and monkeys were 0.25, 0.50, 1.14, and 0.49 micrograms/ml, respectively, with mean elimination half-lives of 5.0, 3.8, 8.0, and 11.7 h, respectively. The oral bioavailability of AT-4140 calculated from the ratio of the areas under the concentration-time curve after oral and intravenous administration was 77% in dogs. The levels of AT-4140 in tissue in mice and rats were 1 to 11 times higher than the levels in plasma and 4 to 9 times higher than those of ciprofloxacin in mice. The mean 24-h biliary recovery of AT-4140 in rats was 5.6% of the dose and became 21.3% after beta-glucuronidase treatment. The mean 48-h urinary recoveries of AT-4140 in mice, rats, dogs, and monkeys were 6.7, 12.9, 8.6, and 12.7%, respectively, of the dose and were 7.8, 16.3, 8.9, and 18.9%, respectively, after beta-glucuronidase treatment. The pharmacokinetics of AT-4140 may be characterized by its good tissue penetration and its long half-life in plasma and tissues.

Effect of theophylline on monoamine metabolism in the rat brain.

The effect of theophylline on brain monoamine metabolism was studied in rats. Single doses of theophylline caused a striking and dose-related increase in the levels of 3-methoxy-4-hydroxyphenylethylene glycol sulfate (MOPEG-SO4) and 5-hydroxyindoleacetic acid (5-HIAA) in the brain. The level of brain homovanillic acid was only slightly affected. No appreciable change occurred, however, in the levels of brain norepinephrine, serotonin and dopamine. The increased level of brain MOPEG-SO4 or 5-HIAA after theophylline does not appear to result from its interference with the transport system for the acids in the brain since the rate of decline of the acid levels following pargyline was not affected. Under the conditions of brain monoamine oxidase inhibition, theophylline enhanced the increase in brain normetanephrine level without causing any change in 3-methoxytyramine level. The enhancement of brain normetanephrine level by theophylline became more pronounced when rats were pretreated with imipramine in addition to pargyline. These results suggest that, in the brain, theophylline may cause a release of serotonin leading to its increased turnover. The results also confirm the previous conclusion that the methylxanthine causes a release of norepinephrine and a concomitant increase in its turnover in the brain.

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).

Zonisamide: Pharmacology and Clinical Efficacy in Epilepsy

The discovery of zonisamide (ZNS) did not result from a search for new antiepileptic drug (AED). A continuous random screening for anticonvulsant activity had been in progress for many years at the research laboratories of Dainippon Pharmaceutical Co., Ltd. ZNS was discovered by serendipity in 1974 during routine testing of 1,2-benzisoxazole derivatives which were synthesized for the management of psychiatric diseases (49,101). Among the derivatives tested, some compounds including ZNS, were found to have a potent anticonvulsant activity in experimental animals. ZNS has a benzisoxazole structure that distinctly differs from any existing AED. The chemical structure of ZNS is shown in Fig. 1. After comprehensive preclinical studies, clinical development of ZNS in Japan started in September 1979. ZNS was approved for the control of partial seizures and generalized seizures in March and launched in June, 1989, in Japan. ZNS was introduced to the Korean market in 1992. In the United States, a New Drug Application (NDA) was submitted in March 1997. The Food and Drug Administration (FDA) issued an approvable letter to the company in March, 1998, for use as adjunctive therapy in the treatment of partial seizures in adults with epilepsy (80). This review will focus mainly on the pharmacodynamic properties of ZNS and its clinical efficacy in epilepsy.

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.

Mode of Incomplete Cross-Resistance Among Pipemidic, Piromidic, and Nalidixic Acids

Spontaneous mutants with various patterns of resistance to pipemidic acid (PPA), piromidic acid (PA), and nalidixic acid (NAL) were isolated from Escherichia coli K-12. Most mutants were less resistant to PPA than to PA and NAL, and some mutants resistant to PA and NAL were hypersusceptible to PPA. As for the mutants tested, resistance to the drugs was conferred by mutations at nalA and new nal genes designated as nalC and nalD, both of which were located at about 82 min on the recalibrated map. Resistance to PA and NAL was due to decreased sensitivity of the bacterial DNA synthesizing system to them and insufficient drug transport, whereas resistance to PPA was only due to the former.

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

Some altered responses in rats formerly dependent on morphine

This investigation examined whether or not physical dependence or other abnormalities were detectable 1–3months after withdrawal in dependent rats that had been treated with the morphine (maintenance dose of 100×2mg/kg/day,s.c.) for 7 weeks. When narcotic antagonists were administered on the 32nd day after withdrawal, nalorphine caused a dose-dependent increase in spontaneous locomotor activity and a complete inhibition of wet-dog shakes and the writhing syndrome. Naloxone was ineffective. A remarkable increase in spontaneous locomotor activity on the 67th day and a significant increase in body weight on the 69th and 92nd day after withdrawal occurred after an acute injection of morphine (10 mg/kg, s.c.). When morphine (10 mg/kg) was administered for 3 days from the 92nd day after withdrawal, withdrawal from morphine produced a significant decrease in body weight. When morphine (10 mg/kg) was administered for 3 days from the 102nd day after withdrawal, a levallorphan injection caused a significant decrease in spontaneous locomotor activity and an increase in the frequency of the diarrheal syndrome. These abnormal responses, not observed in the naive rats, suggest the remains of some behavioral and biochemical abnormalities 3 months after morphine withdrawal.