A combined use of deuterium labelling and recently developed scanning thinlayer chromatography/matrix-assisted-secondary-ion mass spectrometry(TLC/SIMS) was applied for identification of metabolites of zonisamide in rat urine. Zonisamide with deuterium distribution of d₂/d₃/d₄=1/2/1 were prepared and orally given to rats at the dose of 40 mg/kg. Metabolites were extracted from 48 hr-urine and subjected to TLC/SIMS. The specific distribution of deuterium made easy the identification of the urinary metabolites by simple inspection of the spectrum for the presence of triplet ion clusters.
In rat urine unchanged drug and three metabolites, N-acetyl-3-sulfamoylmethyl-1, 2-benzisoxazole, 1, 2-benzisoxazoel-3-carboxylic acid, and the sulfate of (2-hydroxybenzoyl)methanesulfonamide, were identified, and the presence of a polar conjugate of unchanged drug was suggested. Cleavage of N-O bond in benzisoxazole ring was demonstrated.

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Metabolite composition in rat plasma, tissues, urine and bile was studied by TLC radiochromatography after oral administration of [¹⁴C]zonisamide at 20 mg/kg. Metabolites excreted with dog and monkey urine were analyzed by TLC-radiochromatography and mass spectrometry.
Radioactivity in rat plasma, erythrocytes and preputial gland virtually consisted of unchanged zonisamide both after stngle and consecutive administration. More than 4 metabolites were detected in rat urine : the major component was unchanged zonisamide. The composition was not significantly different after intravenous administration. Unchanged zonisamide was detected as a major radioactive component also in the bile. Metabolite composition in dog and monkey urine was rather different from that in rat, however, major component in common was unchanged zonisamide. Besides zonisamide, N-O cleaved compound, hydroxylated zonisamide, acetylated zonisamide and carboxylic acid compound were identified by mass spectrometry.

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Metabolic studies were conducted on ¹⁴C-labeled indometacin farnesil (¹⁴C-IMF) and ¹⁴C-indomethacin (¹⁴C-IND) in rats. The uptake of IMF into target cells and release of IND from IMF were also examined in vitro using ³H-IMF and ³H-IND in cultured rat snovial cells.
1. ¹⁴C-IMF, administered orally, was absorbed mainly from intestinal tract via thoracic lymph duct (12% of the dose) as unchanged from. The extent of gastrointestinal absorption was estimated to be about 20% of administered dose based on the lymphatic and portal vein absorption.
2. The level of radioactivity in the blood reached the maximum of 2.80 nmol/ml at 6 hr, followed by gradual decrease after administration of ¹⁴C-IMF dissolved in sesame oil. The extent of absorption of IMF decreased at doses greater than 5 mg/kg.
3. Maximum concentrations in the most tissues were reached at 4-6 hr after ¹⁴C-IMF dosing. The liver had the highest radioactivity level exceeding about 3 times that in the plasma, followed by adrenal and spleen with 1.5 times higher levels than in plasma at 4 hr after dosing. From these results, it was demonstrated clearly that IMF was distributed into the tissues as on unchanged form at higher levels than that in plasma, although IND was in plasma.
4. In vitro plasma protein binding of IMF to dog and human plasma was more than 98 %.
5. The uptake of IMF by cultured synovial cells was more than 70-fold greater than that of IND, and IMF was hydrolyzed to IND in the cells. The hydrolytic enzyme activity towared IMF in the cells was induced by the addition of PMN factor to the cultured medium.
6. IMF was found to be metabolized mainly by the hydrolysis of ester bond and with further release the active metabolite, IND.
7. About 14% and 91% of radioactivity were excreted in urine and feces. respectively.

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The absorption, distribution, metabolism and excretion of ¹⁴C-labeled indometacin farnesil (¹⁴C-IMF) was studied after daily oral administration of 5 mg/kg for 14 days.
Blood level of radioactivity 6 hr (T_max) after administration reached plateau at 3rd dosing and the levels were about 1.2 times higher than that after the first administration. On other hand, the blood levels at 24 hr increased about 2 times during experimental period. The concentrations of radioactivity in most tissues at 6 hr after the 14th administration were attained less than 2 times for the single administration. The levels of unchanged IMF were high in tissues such as liver, adrenal and spleen, and IND released from IMF was present in plasma and kidney. These levels in plasma and tissues increased slightly by repeated administration and decreased gradually after the final dose. The excretion of radioactivity into urine and feces was 10-13% and 82-85% of administered dose, respectively, during experimental period. Composition of fecal and urinary metabolites after repeated administration were similar to those after the single administration.
Based on above results, it was indicated that metabolic fate of ¹⁴C-IMF was not altered by repeated administration.

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The absorption, distribution, metabolism and excretion of ¹⁴C-labeled indometacin farnesil (¹⁴C-IMF) was studied in dogs after oral administration at the dose of 100 mg/dog or 258 mg/dog.
The peak blood concentration of radioactivity was attained at 2 hr and 8 hr after administration. The later peak was due to indomethacin (IND) released from IMF, which was suggesting the enterohepatic circulation of IND was occurred.
Radioactivity distributed into the liver, spleen and kidney was higher than that in plasma at 2 h after the ¹⁴C-IMF dosing. More than 74% of radioactivity was present as unchanged IMF in plasma, spleen, adrenal and adipose tissue, and more than 51 % in intestinal mucosa, liver and stomach mucosa, in contrary kidney in which IND and its metabolites were mainly present. Concentration of radioactivity, IMF and IND in synovial tissue at 4 hr after administration attained 0.42, 0.24 and 0.06 nmol/g, respectively, and IMF level in the tissue was about 4 times lower than that in plasma.
Subcellular distribution studies of radioactivity in liver, stomach and intestine mucosa revealed that, IMF was mainly associated with cellular membrane fraction of these tissues while IND with the cytosolic fraction.
Approximately 89 % and 11 % of administered radioactivity were excreted in feces and urine, respectively, during 7 days after administration. Radioactivity in feces consisted mainly of unchanged IMF and that in urine was mainly desbenzoyl-IND.

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The metabolism of an antiallergic agent, 1-(2-ethoxyethyl)-2-(hexahydro-4-methyl-1H-1, 4-diazepin-1-yl)-1H-benzimidazole difumarate (KG-2413), was studied in rats and guinea pigs after oral administration of the ¹⁴C labelled compound.
KG-2413 and its metabolites in the urine, bile, plasma and liver of rats were quantified. The major metabolites of KG-2413 in rats were 5-hydroxylated compound (M 5 b), 6-hydroxylated compound (M 5 a) and their conjugated metabolites. Tracer concentration of the unchanged drug was found, so it was assumed that KG-2413 was rapidly metabolized in rats.
The urinary metabolites in guinea pigs were also quantified. The major metabolite was N-oxide compound (M9), and M 5 a and M 5 b were present mostly as conjugated metabolites, but the amounts of them were about one sixth of M9. The urinary excretion of the unchanged drug in guinea pigs was higher than that in rats.
There were remarkable interspecies differences in the urinary excretion of the metabolites after oral administration of KG-2413.

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Absorption, metabolism and excretion of an antiallergic agent, 1-(2-ethoxyethyl)2-(hexahydro-4-methyl-1H-1, 4-diazepin-1-yl)-1H-benzimidazole difumarate (KG-2413), were investigated in dogs.
The plasma levels of radioactivity reached the maximum at 1 h after oral administration of ¹⁴C labelled KG-2413 at a dose of 2 mg/kg, and then declined in three-exponential manner. After intravenous administration of 2 mg/kg, the plasma levels of radioactivity temporarily rose at the initial stage of dosing, and then delined in three-exponential manner. No difference was observed between half-life times of radioactivity following administration by both routes.
The area under the plasma concentration-time curve of radioactivity and the radioactivity excreted into the urine after oral administration were close to those after intravenous dosing.
The plasma levels of unchanged KG-2413 accounted for only about 1 % of total plasma radioactivity even at the initial stage of oral dosing. About 25 % of total plasma radioactivity was related to the N-oxide compound (M 9) over 6 h after dosing.
In the both dosing routes, the radioactivity was mainly excreted into urine, and the cumulative urinary and fecal radioactivity accounted for 97 % of administered dose within 96 h.
After oral administration, the major urinary metabolites of KG-2413 found in dogs were M 9 and the 6-hydroxylated compound (M 5 a), while M 5 a and the 5-hydroxylated compound (M 5 b) in rats and M 9 in guinea pigs. A remarkable interspecies differences in the metabolism of KG-2413 were observed.

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Absorption, metabolism and excretion of Y-516, a new psychotropic drug, were investigated in male dogs after administration of ¹⁴C labeled compound (¹⁴C-Y-516).
Y-516 was rapidly absorbed from the gastrointestinal tract, and the absorption extent was estimated to be about 60% based on AUCs of plasma radioactivity levels after oral and intravenous administration.
The highest plasma level of radioactivity (1.42 μg-eq/ml) was observed within 45 min after oral administration of 5 mg/kg.
Approximately 84 ?? 91 % of radioactivity in the plasma was bound to the proteins. A small transition of radioactivity to the blood cell was observed.
The major metabolic pathways of Y-516 in dogs are considered to be the hydroxylation at the iminodibenzyl ring, and the dehydrogenation at the terminal spiroamine moiety.
No significant qualitative difference in the metabolism of Y-516 was observed between dogs and rats¹⁾.
When ¹⁴C-Y-516 was orally administered to dogs, approximately 4.5% and 90.3 % of radioactivity was excreted within 5 days in urine and feces, respectively.

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Aromatase is the cyt. P-450 enzyme that mediates the biosynthesis of estrogens from androgen precursors. A large number of steroids have been evaluated as potential aromatase inhibitors, and they are classified into three groups, competitive inhibitor, affinity label and suicide substrate, according to their inhibition manner. Specific inhibitors of this enzyme have application as research tools for investigating aromatization mechanism, and are of pharmacological interest because of their possible use for treatment of estrogen-dependent deseases such as breast cancer and benign prostatic hyperplasia. Biochemical aspects of the activity of known steroidal aromatase inhibitors, their structure-activity relationships and their use for clinical treatment are discussed.

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