The previous studies have shown that there was the species difference between rat and mouse inthe metabolic fate of KBT-3022, and that the O-demethylation of two methoxyphenyl groups of desethyl KBT-3022 (M9) was main metabolic pathway. The study of metabolism of M9 by rat liver, lung, kidney and small intestine 9, 000×g supernatant suggested that liver was the most active metabolizing organ.
In this study, we have investigated the in vitro metabolism of M9 using 9, 000×g supern atant of liver homogenates of male rats and mice in order to clarify the species difference in the metabolic fate of M9.
The metabolic activity of M9 and the O-demethylase activity of 9, 000×g supernatant of liver homogenates of rats were much higher than those of mice. The activity of demethylation of 5 methoxyphenyl group of M9 was higher than that of 4-methoxyphenyl group, both in rats and mice. However, in the demethylation of monodesmethylated M9 in rats, the activity of demethylation of 4-methoxyphenyl group was higher than that of 5-methoxyphenyl group.
These results suggest that the species difference in the demethylation of M9 by 9, 000×g supernatant of liver homogenates relates to the species difference in the metabolic fate of KBT-3022.

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Absorption and excretion of ¹⁴C-AE0047, a new dihydropyridine calcium antagonist, were studied in rats and dogs after oral or intravenous administrations.
1. When ¹⁴C-AE0047 was administered to male rats at a dose of 3.0 mg/kg orally, the concentration of radioactivity and the unchanged AE0047 in plasma reached the C_max of 1.34μg eq./ml and 0.92μg/ml, respectively, at 3.3 hr, and then decreased with half-life of 4.5 to 5.2 hr until 24 hr. The absorption rate and bioavailability of the ¹⁴C-AE0047 in rats were calculated to be about 24.5% and 22.0%, respectively.
At 2 hr after an oral administration of ¹⁴C-AE0047 to male dogs at a dose of 3.0 mg/kg, the concentration of radioactivity and the unchanged AE0047 in plasma reached the C_max of 1.29μg eq./ml and 0.73μg/ml, respectively, and then decreased with half-life of about 12 hr. The absorption rate and bioavailability of the ¹⁴C-AE0047 in dogs were calculated to be about 23.9% and 21.2%, respectively.
2. When ¹⁴C-AE0047 was administered to fasting male rats at dose range of 0.1 to 6.0 mg/kg, the bioavailability values increased according to a dose-escalation, suggesting the metabolism of AE0047 in liver is saturable.
3. The AUC of ¹⁴C-AE0047 under the non-fasting condition decreased to one-third compared to that under the fasting condition, indicating the effect of food intake on the absorption in rats.
4. In consecutive oral administrations of ¹⁴C-AE0047 for 14 days to rats, the levels of radioactivity in blood tended to increase gradually with dosing times. After the 14th administration, both C_max or AUC increased to 1.7 to 1.8 times, but the radioactivity was eliminated from the blood with the constant half-lives irrespective of dosing times.
5. The excretion of radioactivity in the urine and feces of rats within 168 hr after oral administration was 4.2% and 96.1% of dose, respectively. In the bile-duct cannulated rats, biliary excretion was 10.86%, and 9.03% of the radioactivity excreted into bile was re-absorbed. On the consecutive administrations, the excretion of radioactivity into urine and feces was almost constant, being 3.2% and 96.1%, respectively.
The excretion of radioactivity in the urine and feces within 168 hr after an oral administ ration to dogs was 11.1% and 83.2%, respectively.
6. In the plasma of rat and dog, the unchanged AE0047 was mainly detected. After oral administration to rats, M1 and M6 were observed as minor metabolites in plasma, and M3 was detected as a major metabolite in urine. In the urine of rats, the unchanged AE0047 was not detected.

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The tissue distribution of ¹⁴C-AE0047 in rats was studied after single or consecutive oral administrations by the whole body autoradioluminography and by the excised tissue-liquid scintillation method. The transfer of ¹⁴C-AE0047 to lymphatic system during the absorption was also investigated.
1. The maximum levels in the lymph, liver and adrenals, which showed higher levels of radioactivity than other tissues, except gastro-intestinal tract, were found at 3 hr, and the levels of radioactivity in muscle, fat, brown fat, skin, bone marrow, testis and eyeball reached the maximum at 6 hr after an oral administration of ¹⁴C-AE0047. The level of radioactivity in central nervous system was the lowest. The radioactivity in plasma decreased with a half-life of about 1.2 day, and those in each tissue did with half-lives of 2 to 4 days.
2. The tissue distribution pattern obtained after consecutive doses of ¹⁴C-AE0047 for 14 days was similar to that after a single dose. Almost all tissues, except the adipose tissue, bone marrow and mesenteric artery, showed 3 to 6 times higher radioactivity levels than after a single dose, which were almost the same values as the predicted accumulation factor. No particular accumulation of radioactivity in main tissues was observed after the consecutive oral administration of ¹⁴C-AE0047.
3. The radioactivity, 5.3% of the dose, transferred to lymph recovered from the thoracic duct within 48 hr after an oral dosing to rats.

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The transfer of radioactivity to fetus and milk were studied in the pregnant or lactating rats after a single oral administration of ¹⁴C-AE0047 at the dose of 3 mg/kg. The localization of the radioactivity was visualized by whole body autoradioluminography and was determined by the excised tissue-liquid scintillation method.
1. When ¹⁴C-AE0047 was administered orally at a dose of 3 mg/kg to pregnant rats (19th day of gestation), the maximum levels of radioactivity in the fetus were observed at 6 hr after the administration and accounted for 6.0% of the C_max present in the maternal plasma. The amounts of radioactivity transferred to one fetus was 0.009 to 0.015% of administered dose.
2. When ¹⁴C-AE0047 was administered orally at a dose of 3 mg/kg to lactating rats (the 19th day after delivery), the maximum level in milk was reached at 6 hr and it was lower than that in the maternal plasma.

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Before the start of revise of the present PK guideline in Japan, PK study group of JPMA made inquiries about the present and the newly revised PK guideline (new PK guideline) of Japan to 96 numbers of companies in JPMA. Almost all companies (98.6%) have recognized the meaning of the existence of the present PK guideline, but, on the other hand, all companies (100%) have also pointed out the necessity of alteration of it in the following aspects. 1) The new PK guideline have to touch upon the human pharmacokinetics. 2) Following the progress of molecular biology, molecular species of metabolic enzyme (specially, CYP 450 s) must be elucudated for the expectation of drug-drug interaction. 3) The new PK guideline must be accommodated with the ICH guidances (Toxicokinetics and Repeated Dose Tissue Distribution Studies), and will be harmonized in the sense of international use. 4) The new PK guideline have to contain only the minimum requirements and must be applied flexibly. The Format for NDA in Japan must be also alterated in response to the establishment of the new PK guideline and the ICH guidances.

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Pharmacokinetic data plays an important role in the evaluation of new drugs. They help to extrapolate data of in vitro to those of in vivo, to correlate data of non-clinical pharmacological experiments with those of clinical trials, and also to predict the possibility of drug interaction. The role of pharmacokinetic data in the process of review of pharmacological data in NDA was explained. The purpose of the on-going study to revise Japanese Guidelines for Non-clinical Pharmacokinetic Studies and the discussions in the working group were also introduced.

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