Ipratropium bromide (3α-hydroxy-8-isopropyl-lαH, 5αH-tropanium bromide(±)-tropate) labeled with ¹⁴C was administered orally, intranasally and intravenously to rats and rabbits (5 mg/100μCi/kg) to examine the absorption, distribution and excretion.
The radioactivity in rat blood reached to the highest level of 0.024 μg/ml at 3 hr after oral dosing, 0.025 μg/ml at 4 hr after oral dosing under anesthesia and 0.072 μg/ml at 1 hr after intranasal dosing. The area under the blood concentrationtime curve (AUC) within 24 hr after dosing were 0.273 μg•hr/ml after oral dosing, 0.257 μg•hr/ml after oral dosing under anesthesia, 0.622 μg. hr/ml after intranasal dosing and 8.559 μg•hr/ml after intravenous dosing.
The cumulative urinary excretion in rats was 3.2 ?? 5.9% of dose after oral dosing and 10.2% of dose after intranasal dosing.
The concentration in almost all tissues of rats reached to the highest level during 1 to 6 hr after intranasal administration and 1.9 % of administered radioactivity was retained in nasal cavity at 6 hr after intranasal administration.
The plasma protein binding in rats was 27.5%, 29.6% and 78.6% at 1, 6 and 24 hr after intranasal dosing, respectively and less than 10 % of ¹⁴C-Ipratropium bromide was bound to the plasma protein during in vitro experiment.
The peak blood concentration in rabbits were 0.064 μg/ml at 1 hr after oral dosing and 0.022 μg/ml at 4 hr after intranasal dosing. The AUC within 48 hr after dosing were 1. 105 μg•hr/ml after oral dosing, 0.436 μg•hr/ml after intranasal dosing and 7.141 μg•hr/ml after intravenous dosing.
The cumulative urinary excretion in rabbits was 12.7% of dose after intranasal dosing.
The plasma protein binding in rabbits was 24.5 %, 29.7 % and 57.1 % at 1, 6 and 24 hr after intranasal dosing and less than 10 % of ¹⁴C-Ipratropium bromide was bound to the plasma protein during in vitro study.

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Three new metabolites of budralazine, an antihypertensive drug, were isolated from urine, bile and liver-perfusion effluent of rats, and their structures were identified by direct comparison with authentic samples.
A major urinary metabolite was identified as the mercapturic acid conjugate of mesityl oxide, namely, N-acetyl-S-(1, 1-dimethyl-3-oxo)butyl-L-cysteine (M-14).
A major biliary metabolite was identified as 1-[2-(1, 3-dimethyl-3-S-L-glutathionyl-butylidene)hydrazino]phthalazine(M-15). It was assumed that M-15 was derived from addition of glutathione to the terminal carbon-carbon double bond of budralazine. M-15 had two geometrical isomers with respect to the hydrazone linkage. Two isomers were clearly separated by HPLC.
A major metabolite of liver-perfusion was confirmed as the carboxylic acid analogue of budralazine, namely, 4-(1-phthalazinyl)hydrazino-2-methyl-trans-2-pentenoic acid (M-16). M-16 was also found to be a major plasma metabolite.

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The machanism of intestinal absorption of amino-β-lactam antibiotics was studied using ¹²⁵I labelled cefatrizine of high radioactivity in rat by in situ ligated loop method and in vitro intestinal segment method. Iodocefatrizine (¹²⁵I-CFT) retained the same antimicrobial activity and intestinal permeability as cefatrizine.
¹²⁵I-CFT was taken up by the tissue against a concentration gradient. The tissue accumulation of ¹²⁵I-CFT was highly temperature dependent and was inhibited by metabolic inhibitors. The rate of ¹²⁵I-CFT uptake was decreased in the presence various amino-cephalosporins, amino-penicillins and dipeptides in the medium, but not affected by mono-carboxyl cephalosporins and amino acids. These results demonstrate that ¹²⁵I-CFT is absorbed through the intestinal tissue by the carriermediated transport system.
In addition, the usefulness of application of ¹²⁵I-labelled compounds, which can be easily prepared with very high specific radioactivity, in the biochemical pharmacology studies was also exemplified.

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¹⁴C-L-DOPS labelled at C-3 position was orally administered to pregnant rats or lactating rats to examine foeto-placental transfer and excretion of radioactivity into the milk.
1. After oral administration of ¹⁴C-L-DOPS (10 mg/kg) to pregnant rats, no radioactivity was detected in the fetus on 13th gestation day, but nearly the same ¹⁴C level as that in the mother was detected on 20th gestation day. The major metabolite in serum of the fetus was 3-OM-DOPS.
When ¹⁴C-L-DOPS (10 mg/kg/day) was orally administered to pregnant rats, from 14th to 20th gestation day, ¹⁴C levels in serum and tissues were found to be substantially similar to those after a single administration.
3. When ¹⁴C-L-DOPS (10 mg/kg) was orally administered to lactating rats, ¹⁴C was transfered from blood to milk mainly as the intact drug.

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1. After a single oral administration of ¹⁴C-L-DOPS (10 mg/kg), substantially no differences in serum ¹⁴C levels, ¹⁴C excretion and urinary excretion rates of motabolites were found between aged (53 weeks old) and young adult (7 weeks old) rats.
2. Acute renal failure in rats was induced by the subcutaneous administration of mercuric chloride (2 mg/kg). After a single oral administration of ¹⁴C-L-DOPS (10 mg/kg) to rats with renal failure, serum ¹⁴C concentrations rose untill 8 hours and the area under the serum ¹⁴C concentration vs time curve was 10 times higher than that of normal rats. Radioactivity was excreted into urine, feces and expired air more slowly but in the similar pattern as compared with normal rats.
3. Serum ¹⁴C levels, ¹⁴C tissue distribution and ¹⁴C excretion in rats were not affected by co-administration of ¹⁴C-L-DOPS (10 mg/kg) with L-DOPA (10 mg/ kg) or with both of L-DOPA (10 mg/kg) and benserazide (2.5 mg/kg). Co-administration of ¹⁴C-L-DOPS with L-DOPA and benserazide gave higher concentrations of L-DOPS and lower concentrations of both NE and HMPG, when compared with co-administration with only L-DOPA.

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A gas chromatographic-mass spectrometric (GC/MS) method for the determination of β-{3-oxo-s-triazolo[4, 3a]pyridin-3(2H)-one}-propionic acid (TPA), a metabolite of trazodone hydrochloride, in biological fluids has been developed. Deuterated analogue of TPA was used as an internal standard. TPA was extracted with ethyl acetate from plasma and urine, and derivatized into a pentafluorobenzyl ester. The reaction mixture was further purified by high-performance liquid chromatography on a reversed-phase column. The eluent containing pentafluorobenzyl ester of TPA and deuterated TPA was collected, and extracted with benzene. GC/MS was carried out by monitoring the molecular ions. The determination limit was 500 pg/ml, and the intra and inter-assay coefficients of variation for the determination of TPA in plasma were 6.7 ?? 9.4% and 7.3 ?? 11.5%, respectively. Plasma levels and urinary excretion were determined by the present method for five healthy volunteers who had received a 50 mg oral dose of trazodone hydrochloride.

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Tissue distribution, especially in brain, was investigated after an injection of ¹²⁵I-iohexol into the subarachnoidal space of the lumbar spinal cord in squirrel monkeys at a dose of 129 mg/kg. Fifteen minutes after administration, a high concentration of radioactivity was found in whole spinal cord, subarachnoidal cisterns, blood, kidney and urinary bladder, but penetration of radioactivity into cerebral cortex was not observed. Three hours after administration, a high concentration of radioactivity was still found in whole spinal cord and subarachnoidal cisterns, and, in addition, a local penetration of radioactivity into the cerebral cortex was clearly observed, howeven at the relatively lower concentration. Twentyfour hours after administration, almost all radioactivity was eliminated not only from cerebrum and upper cerebrospinal cord, but also from almost all of the tissues. It was also confirmed that ¹²⁵ I-iohexol was rapidly transferred from subarachnoidal space into systemic blood and predominantly eliminated into urine via kidney.

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After subcutaneous administration of ¹⁴C-MDP-Lys(L18) to mice, the radioactivity was excreted into urine, feces and with expired air in about 20, 8 and 40 % of the dose, respectively, within the first 48 hours. The main metabolite excreted to the urine and accounting for 15 % of the dose, was identified to be R-_D-lactic acid by the reverse isotope dilution method in which the metabolite was derivatized to p-bromophenacyl ester, recrystallized and separated into enantiomers by HPLC. The configuration of the lactate moiety in MDP-Lys(L18) was retained during the metabolism.
Five metabolites were detected in the liver 5 hours after the administration and 4 of them were identified by TLC as des(GlcNAc)-MDP-Lys(L18), lactic acid, MDP-Lys(L18) and N-acetylmuramic acid in comparison with respective authentic compounds. N-acetylmuramic acid was confirmed further by the reverse isotope dilution method in which it was converted to peracetylated methyl ester and separated by gas chromatography. It was the main metabolite and accounted for 40 % of the radioactivity detected in the liver. MDP-Lys which was supposed to be the pharmacologically active metabolite was not detected.
The metabolic pathway in which MDP-Lys(L18) was mainly metabolized to N-acetylmuramic acid, lactic acid and carbon dioxide, successively, was proposed. Some portion of the drug was converted to lactic acid via des(GlcNAc)-MDP-Lys (L18). A novel cleavage reaction of the ether linkage between the 3 position of sugar and lactic acid moiety in N-acetylmuramic acid was observed.

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Azole antifungal agents inhibit fungal P-450_14DM which catalyzes the 14α-demethylation of lanosterol. Judging from their affinity for the reconstituted lanosterol demethylase system of yeast, azole antifungal agents are classified into two categories. The first one contains potent inhibitors that can quantitatively bind to P-450_14DM and inhibit the demethylase below 0.1 μM. The second one includes weaker inhibitors that require more than 1 μM for complete inhibition of the demethylase. Antifungal agents classified as the first category interfere with binding of CO to ferrous P-450_14DM.
Azole antifungal agents inhibit the lanosterol 14 α-demethylation by rat liver microsomes. These compounds also inhibit other mammalian cytochrome P-450 s such as steroid hormone synthesizing and drug metabolizing enzymes. Affinity of antifungal agents for rat liver demethylase is lower than that for the yeast enzyme especially for the first group compounds. This fact indicates that azole antifungal agents classified as the first category show some selectivity for fungal P-450_14DM. For systemically applicable antifungal agents, selectivity for the fungal enzyme is required for their safety. Accordingly, more extensive studies on interaction between azole antifungal agents and various cytochrome P-450 s are expected.

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The effects of the absorption promoters on two possible pathways, paracellular and transcellular routes, were investigated physiologically or biochemically. Assuming the paracellular route to be a water channel since the permeation through this route related to water absorption, the pore size was obtained from the equivalent pore concept using intestinal everted sac. Sodium caprate, sodium laurate, mixed micelles composed of sodium oleate and sodium taurocholate, EDTA disodium salts, which had larger promoting effects on the intestinal absorption of cefmetazole, fosfomycin and phenol red than other promoters, enlarged the pore size to the extent that inulin could permeate. For the transcellular route, the membrane perturbing actions of the promoters were examined using brush border membrane vesicles, where its protein and lipid portions were labelled with fluorescent probes, and a fluorescence polarization technique. The interaction of the potent promoter such as sodium caprate and membrane protein or lipids was found to cause membrane perturbation and increase the membrane permeability. In this minireview, one methodology for the mechanistic study on drug absorption promotion was introduced as described above. Consequently, the changes in the paracellular and transcellular routes could be found specifically, to explain the in situ absorption promotion of poorly absorbed drugs quantitatively.

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