In the present study, we examined the effects of aging on the pharmacokinetics of ¹⁴Cquinupramine in male rats, following the administration to the aged (2 and 1-year old) and young (8 weeks old) rats.
1. The concentration of radioactivity in blood of young rats reached the maximum 1hr after oral administration. In the older animals, T_max was more delayed. The blood concentration of radioactivity declined with the similar half-life times (T_α1/2=0.87-1.66hr., T_β1/2-19.2 -25.1hr ) in all groups of rats studied. C_max and the area under the blood concentration-time curve (AUC) in the aged rats were 2.8 and 2.7 times higer, respectively, than those in the young rats.
2. Two hours after oral administration of ¹⁴C-quinupramine, the tissue levels of radioactivity in the aged (2 years old) rats were 1.6-10.3 times higher than those in the young rats. The difference became more pronounced 24hr after administration. The distribution pattern of radioactivity in the aged rats was similar to that in the young rats. These findings were consistent with the results of whole body autoradiography.
3. The in vitro plasma protein binding assay of ¹⁴C-quinupramine showed that more than 80% was bound to the protein in every group of animals. In vivo plasma protein binding of radioactivity was 46.5% 2hr and 58.5% lhr after oral administration of ¹⁴C-quinupramine in the aged (2 years old) and young rats, respectivery.
4.The hepatic microsomal drug metabolizing activities (aminopyrine N-demethylation and aniline p-hydroxylation) and the content of cytochrome P-450 in rats decreased with aging. In vitro metabolic study of ¹⁴C-quinupramine with rat liver microsomes revealed that 48.2% and 8.4% of quinupramine remained unchanged in the aged (2 years old) and young rats, respectively.
After oral administration of ¹⁴C-quinupramine, the aged (2 years old) rats showed higher content of the unchanged form in the urine, faces, plasma, heart, liver and kidney than the young rats.
5. Within 24hr after oral administration, the recovery of radioactivity in excreta was 92.4 %, and 66.5% and 51.5% in the young and aged (1 and 2 years old) animals, respectively. The cumulative urinary excretion of radioactivity was 27.5%, 28.1% and 37.2% within 168hr after dosing in the young and aged (1 and 2 years old) rats, respectively.

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The absorption, distribution, metabolism and excretion of isopropyl methyl (±)-2-carbamoyloxymethyl-4-(2, 3-dichlorophenyl)-1, 4-dihydro-6-methyl-3, 5-pyridinedicarboxylate (NB-818) were studied after single oral or intravenous administration of ¹⁴C-labelled compound to male and female rats.
1. After oral dosing (10mg/kg) to male and female rats, the mean peak plasma levels of radioactivity of 5.9 and 11.8μg eq./ml were observed at 1.25 and 3.5hr, respectively. Plasma half-life of radioactivity was 12.0hr in males and 4.7hr in females. After iv dosing (0.3mg/kg), plasma half-life of radioactivity was 13.5 and 6.0hr in males and females, respectively.
2. Plasma levels of unchanged NB-818 reached the maximum concentration at 0.5-1hr after oral dosing (10mg/kg), with the corresponding values of 587 and 906ng/ml, and then declined with half-lives of 2.8 and 2.2hr in male and female rats, respectively. The oral bioavailability of NB-818 in male rats amounted to 33% due to first-pass metabolism.
3. After oral dosing(10mg/kg) to male and female rats, the excretion of the radioactivity in feces and urine during 72hr was 84.0% and 8.0%, 65.1% and 27.5%, respectively. The biliary excretion within 48hr after oral dosing was 52.4% of the dose in males and 56.5% in females. The excretion of the unchanged drug to urine and bile was negligible. Radioactivity was mainly excreted into the feces via the bile and undergone enterohepatic circulation.
4. After oral dosing to male rats, radioactivity was rapidly distributed to various tissues and maintained in high concentrations in the liver and gastrointestinal tract. Radioactivity in most tissues decreased in parallel with that in plasma.
5. The serum protein binding of NB-818 in vitro was more than 98%, and that of radioactivity in vivo was more than 90% after oral dosing in male rats. The binding of radioactivity in vivo to erythrocytes was 9-19% after oral dosing.
6. In the plasma samples of both sexes after oral dosing, M-2 and M-10 were present as the main metabolites. The major metabolite found in rat urine, was M-2. The total amount of M-2 and M-10 in plasma and urine from female rats was much higher than in male rats. In the bile, M-8 was the major component of an identified metabolites. These results indicate that NB-818 was extensively metabolized.
7. A distinct sex-difference in the metabolism and disposition of ¹⁴C-NB-818 in rats was observed.

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The absorption, metabolism and excretion of isopropyl methyl (±)-2-carbamoyloxymethyl-4-(2, 3-dichlorophenyl)-1, 4-dihydro-6-methyl-3, 5-pyridinedicarboxylate(NB-818) were investigated after single oral (1 mg/kg) or intravenous (0.1mg/kg) administration of ¹⁴C-labelled compound to male and female dogs.
1. ¹⁴C-NB-818 was absorbed rapidly and almost completely, after oral dosing to male dogs. The plasma levels of radioactivity reached the peak of 1.24μg equiv./ml at 1.7hr, and then declined biphasically with a terminal half-life of 101.8hr. After iv dosing, the terminal half life was 89.4hr. The pharmacokinetic parameters after iv or oral dosing to female dog were similar to those in male dogs. The radioactivity in the whole blood was lower than that in plasma, but the time-profile was similar to that of plasma.
2. The plasma levels of unchanged NB-818 reached the maximum at 0.5-1hr after oral dosing, with corresponding values of 259 and 201ng/ml, and then declined with half-lives of 2.9 and 2.2hr in male and female dogs, respectively. The oral bioavailability of NB-818 amounted to 65% in male dogs.
3. After oral dosing to male and female dogs, the excretion of the radioactivity in feces and urine during 168hr was 68.5% and 26.3% and 65.4% and 28.5%, respectively. The excretion of radioactivity in feces and urine after iv dosing was similar to that after oral dosing. Fecal excretion was the major excretory route in dogs. The excretion of the unchanged drug to urine was negligible. These results indicate that NB-818 is extensively metabolized.
4. The serum protein binding of NB-818 in vitro was more than 94%.
5. The main components of radioactivity in plasma consisted of the unchanged drug, M-3 and M-5. In urine and feces, M-8 was the major metabolite. The metabolite profiles in urine of male and female dogs were quantitatively similar.
6. No sex difference was observed in the metabolism and disposition of ¹⁴C-NB-818 in dogs.
7. Comparing the metabolism and disposition of NB-818 in dogs to that in rats, a remarkable species difference in the metabolism was observed.

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The absorption, distribution, metabolism and excretion of isopropyl methyl (±)-2-carbamoyloxymethyl-4-(2, 3-dichlorophenyl)-1, 4-dihydro-6-methyl-3, 5-pyridinedicarboxylate (NB-818) were studied after repeated oral doses to rats (10mg/kg/day, 3weeks) and dogs (5mg/ kg/day, 54 weeks).
1. The levels of radioactivity in the plasma at 24hr after each administration of ¹⁴C-NB-818 to male rats increased by repeated dosing until the 18th dosing. The average level after the last dosing was 1.8 times higher than that after the first dosing. The plasma levels of radioactivity after the last dosing reached the peak of 6.4μg equiv./ml at 3.5hr, and declined with a half-life of 11.8hr.
2. At 24hr after the last of 21 daily oral treatments, the concentrations of radioactivity in most of the male rat tissues were 2-14 times higher than those after the single dose. However, the tissue distribution patterns in both cases were similar. Disappearance of radioactivity from the tissues after 21 days of dosing was slower than after single dosing, but radioactivity did not remain in the tissues for a long period.
3. The excretion of radioactivity in urine and feces was nearly constant during the period of repeated administration in male rats. Within 168hr after the last dosing, urinary and fecal excretion amounted to 7.6% and 82.3% of administered dose, respectively.
4. In the case of the repeated oral dosing of NB-818 for 54 weeks to male and female dogs, plasma levels of unchanged drug showed little change.
5. The profile of the urinary metabolites showed no marked change during the period of repeated administration in male and female dogs.

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Metabolites of MCI-9042 were identified and their concentrations in urine and feces were investigated after oral administration of ¹⁴C-MCI-9042 or MCI-9042 (20mg/kg, 100mg/body) to male rats, dogs, monkeys and human.
1. MCI-9042 was firstly hydrolyzed to M-1, and followed by O-demethyla tion, N-oxide formation, N-demethylation, deamination and hydroxylation to two aromatic rings resulting in formation of eleven metabolites. Furthermore these metabolites finally formed own glucuronides or sulfates.
2. After oral administration of ¹⁴C-MCI-9042 to male rats and dogs, almost dosed radioactivity was excreted into feces. Major metabolites in rats were M-1, M-2, M-4, M-10 and these conjugates. In dogs, 34% of dosed radioactivity was excreted to feces in the form of M-1, suggesting that the rate of M-1 metabolism in dogs was slower than in rats. 3. After oral administration of MCI-9042 to male monkeys and human, metabolites were mainly excreted into urine. Major metabolites in monkeys and human were conjugates of M-1, M-2, M-4, M-5 and M-10.

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The absorption, distribution, metabolism and excretion were investigated in male and female rats after single oral or intravenous administration of ¹⁴C-MCI-9042.
1. When ¹⁴C-MCI-9042 was administered orally at the dose levels of 5, 20 and 100mg/kg to male rats, areas under the time versus plasma concentration curves (AUC₀^∞) of radioactivity and unchanged MCI-9042 correlated well with administered doses.
2. MCI-9042 was absorbed rapidly and almost completely (more than 90% of dose) from the digestive tract.
3. After oral administration of ¹⁴C-MCI-9042(20mg/kg) to male and female rats, plasma levels of radioactivity and unchanged MCI-9042 reached maxima at 15min after administration and decreased rapidly with the half-lives of t_1/2α=0.23 ?? 0.32hr and t_1/2β=4.7 ?? 6.1hr (radioactivity), t_1/2α=0.14 ?? 0.16hr and t_1/2β=0.88 ?? 1.82hr (MCI-9042), respectively. The bioavailability in male rats was estimated based on the AUC₀^∞ of unchanged MCI-9042 after oral and intravenous (3 mg/kg) administration, and appeared to be 33%.
4. In the liver, kidney and lung, except the digestive tract, the level of radioactivity was higher than that observed in plasma, however there was rapid elimination of radioactivity from tissues.
5. Radioactivity was excreted mainly into the bile(83 ?? 88%)and 69% of it was reabsorbed.
6. Sex-related differences were observed in rats, as manifested by more rapid decrease of unchanged MCI-9042 and M-1 in the plasma of male rats, and greater excretion rate of radioactivity into urine in female rats.
7. Radioactivity was excreted completely into urine and feces. Main excretion route in rats was fecal excretion.

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The absorption, distribution, metabolism, excretion and accumulation of MCI-9042 were investigated after repeated oral administration of ¹⁴C-MCI-9042 (20mg/kg/day) to male rats for 21 days. The effect of MCI-9042 on the hepatic drug-metabolizing enzyme activities was also investigated after repeated oral administration of MCI-9042 (20 or 100mg/kg/day) to male rats for 21 days.
1. The Tmax and Cmax of radioactivity in the blood after single oral administration to unfasted rats were delayed and decreased compared with those after single administration to fasted rats. Area under the time versus blood concentration curve (AUC₀)^∞ of radioactivity in unfasted rats was decreased about 18% compared with that in fasted rats.
2. Blood levels of radioactivity at 30 min after each dosing were nearly constant during repeated administration, and those at 24hr after each dosing were increasing up to the 12th day and then after reaching plateau remained constant. The half-life of blood levels of radi oactivity after 21 days repeated oral administration was 10.3hr (t_1/2β), which was almost similar to that after single administration.
3.The tissue levels of radioactivity at 24hr after each dosing increased gradually till the 7th or 14th administration, and thereafter remaining at almost same levels. The tissue levels of radioactivity after 21 days repeated administration decreased gradually.
4. The excretion rates of radioactivity into the urine and feces were nearly constant during the period of repeated administration of ¹⁴C-MCI-9042. Within 96hr after the last dosing, 21.8% and 74.3% of the administered radioactivity were recovered into urine and feces, respecti vely.
5. The percentage of unchanged MCI-9042 and its metabolites to total radioactivity present in the plasma, liver, urine and feces after repeated administration were almost same as tho se after a single administration.
6. After repeated administration of MCI-9042 for 21 days, any effect on the hepatic micro somal drug-metabolizing enzyme system was not observed.

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The absorption, metabolism and excretion of MCI-9042 were investigated in male and female dogs after oral (20mg/kg) or intravenous (1 mg/kg) administration of ¹⁴C-MCI-9042.
1. After oral administration of ¹⁴C-MCI-9042 to male and female dogs, both the plasma levels of radioactivity and unchanged MCI-9042 reached maxima at 15 ?? 45 min, and then decreased with half-lives (t_1/2β) of 10.3 ?? 10.7hr and 1.5 ?? 1.6hr when determined based on radioactivity or unchanged MCI-9042, respectively. The absorption rate and bioavailability calculated from areas under the time versus plasma concentration curves (AUC₀^∞) of radioac tivity and unchanged MCI-9042 after oral or intravenous administration were 84% and 57%, respectively.
2. After oral administration to dogs, M-1, M-6 and M-8 were detected in the plasma, and other free metabolites were not observed.
3. In both male and female dogs, approximately 100% of dosed radioactivity was excreted into urine(26 ?? 31%) and feces (71 ?? 74%) within 120hr after oral and intravenous administration of ¹⁴C-MCI-9042.
4. Both blood or plasma levels and excretion rates were not affected by sex-related phenomena in dogs.

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Salazosulfapyridine (Sulfasalazine, SASP, 2-hydroxy-5-[[4-[(2-pyridinylamino) sulfonyl] phenyl] azo] benzoic acid) labelled with ¹⁴C in the carboxyl group and with ³H in chemically as well as metabolically stable positions in the benzenesulfonyl ring was administered either intravenously or orally to male and female rats in order to study the plasma pharmacokinetics of SASP and the plasma profiles of the metabolites. After intravenous administration SASP was eliminated rapidly from plasma with a half-life (t_1/2) of 8min. The volume of distribution (Vd_ss) of SASP was 0.2l/kg and total clearance (CLtot) was 18ml/min × kg. After oral administration, SASP was present in plasma mainly during the first 4 hours. The time for maximal concentration (T_max) varied for SASP between 1 ?? 3 hours, for ¹⁴C, corresponding to 5ASA metabolites, between 3 ?? 10 hours and for ³H, corresponding to sulfapyridine metabolites, between4 ?? 12 hours. The inter-individual variation was considerable. The bioavai lability of SASP was 9% and independent of the dose. The maximal concentration(C_max) and area under the curve (AUC) increased proportionally with the dose. The absorption of SASP was not influenced by fasting overnight.
There was a clear sex difference in the metabolism of SASP. The plasma concentration of sulfapyridine metabolites in female rats was twice that in male rats. No hydroxylated metabolites were found in female rat plasma, whereas in the male rats, the hydroxylated sulfapyridine metabolites were the major metabolites.

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The tissue distribution has been studied in rats of both sexes by whole body autoradiogra phy and by dissection of organs after both a single oral and single intravenous administration of radiolabelled salazosulfapyridine (sulfasalazine, SASP). The compound was labelled in two different positions : ¹⁴C in the carboxyl group in the salicylic acid part of the molecule and ³H in the sulfonamide part of the molecule making it possible to follow the metabolites after cleavage of the azobridge.
The results of these investigations showed that following oral administration, the drug remained mainly in the gastro-intestinal tract. At about 8 hours a certain tissue distribution was noticed for both ¹⁴C and ³H. The distribution pattern was very different for the two labellings : the ¹⁴C radioactivity was at that time heterogeneously distributed to certain tissues as liver, bone marrow, intestinal mucosa, kidney, lung, connective tissues, ovary, salivary and harderian gland, while the ³H radioactivity was evenly distributed to all tissues including the central nervous system. The radioactivity was almost eliminated from the tissues within 24 hours.
Also after i.v. injection high concentration of radioactivity was found in the gastrointestinal tract. Already 5 min after administration 25% of the dose was found in the duodenum and 30% in the liver, indicating an extensive biliary excretion. Beside the gastrointestinal tract the highest radioactive concentrations were found in the liver, connective tissues, lung, kidney, and blood. The radioactivity of ¹⁴C labelled SASP decreased more rapidly than that of the ³H. The distribution pattern was roughly the same when comparing males and female rats. In the fetal tissues the ³H radioactivity passed the placental barrier at 4 hours after the injection and was distributed evenly in the fetal tissues, while the ¹⁴C radioactivity was only found in the fetal intestines in small amounts.
Trace amounts of excreted radioactivity was found in milk. The milk to plasma ratio for ¹⁴C was 0.13±0.01 20 min after intravenous administration.
The total recovery of excreted radioactivity in male rats at different doses was 73 ?? 89% for ¹⁴C and 79 ?? 92% for ³H. ¹⁴C radioactivity was mainly found in the faeces while the ³H activ ity was found in about the same amount in faeces and in urine. Female rats had less faecal excretion than males. Only trace amounts of radioactivity were found in the expired air.

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The metabolites formed from [³H, ¹⁴C]salazosulfapyridine (sulfasalazine, SASP), were investigated in urine, faeces, bile and ten different organs from rats after a single oral or intravenous dose. The metabolites were fractionated by liquid chromatography and conclusively identified by mass spectrometry. The metabolites identified in urine were 5-aminosalicylic acid(5ASA), 5-acetamidosalicylic acid(Ac5ASA), sulfapyridine(SP) and 5-hydroxy-sulfapyridine (SPOH) together with glucuronide, sulphate and/or acetyl conjugates of SPOH. The female rats formed no or very small amounts of hydroxylated and conjugated metabolites compared to male rats.
The collected organs and their major metabolite content were as follows : stomach(SASP), duodenum (SASP and SP), ileum (SASP and SP), caecum(SP, SPOH and AcSPOH), colon (SP), lung (SP and SASP), liver (SP, AcSP and SASP), kidney (SP, AcSP and SASP), thyroid (SASP) and testis (SP and AcSP).
The metabolites found in bile after an oral dose were SP, AcSP and glucuronide and sulphate conjugates of these as well as Ac5ASA and unchanged SASP. The bile from male rats contained higher concentrations of conjugated metabolites than bile from female rats. Only intact SASP was found after the i.v. dose.
The cumulative excretion of [¹⁴C, ³H]SASP was studied in bile collected during 24 hours after p.o. or i.v. administration. The recovery of total radioactivity in bile from female rats after i.v. administration was 101.6±1.8%(mean±SEM)and 103.5±1.4% of administered dose for ¹⁴C and ³H respectively. The corresponding figures for male rats were 88.0±4.1% for ¹⁴C and 88.1±4.2% for ³H. The excretion of SASP in bile after i.v. administration was 99.8 % of the administered dose in female rats and 85.9% in the male rats. After an oral dose the biliary excretion of ¹⁴C radioactivity representing SASP and5ASA metabolites was low, 3.86±0.79% for females and 5.71±0.95% for male rats. The ^3H excretion including SASP but consisting most of SP metabolites was significantly higher in the male rats, 38.3±3.7% compared to 10.5±2.1% in female rats. The reason for this sex differences was the formation of hydroxylated SP and further conjugation in male rats. The biliary excretion of SASP after oral administration was similar in both sexes 2.74±0.37% for female rats and 2.52±0.45% for male rats. Since the biliary excretion of the unchanged drug was < 3 % after p.o. administration enterohepatic cycling was not studied.
In conclusion, SASP underwent azoreduction to form 5ASA and SP. Both these metabolites were acetylated. SP was also hydroxylated particularly in the male rats. The SPOH was conjugated both with sulfate and glucuronic acid.

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Repeated daily oral doses of [¹⁴C, ³H]salazosulfapyridine 50mg/kg b.w. was given to male and female rats during 21 days to investigate the absorption, tissue distribution and elimina tion of SASP and metabolites. The peak plasma level of radioactivity was slightly increased for both ³H and ¹⁴C during repeated administration although the increase was not statistically significant. The elimination rate from plasma was similar after the last 21st dose as after a single dose. Thus the 24 hour plasma level was not increased. The concentration of unchanged SASP in plasma was too low to be measurable by liquid chromatography. There was no significant binding of radioactivity to the erythrocytes after the first dose, but after repeated doses some distribution of ¹⁴C to the blood cells was seen.
The dominating picture of the tissue distribution was that most of the radioactivity remained in the gastrointestinal tract. Even 96 hours after the last dose, when only trace amounts of radioactivity remained, the highest radioactivity was found in caecum.
Except for the gastrointestinal tract, the concentration of radioactivity was initially lower in the tissues than in plasma and was dominated by ³H. The concentration of ³H in tissues in relation to the plasma concentration was not changed during the repeated administration. However, the ¹⁴C concentration increased.
The tissue distribution was also studied by autoradiography and image analysis after the same pretreatment as above and with a final high dose of [³H]SASP. The time points studied were 4, 16, and 96 hours after the last given dose. The highest uptake was noticed in the connective tissues, the lung, the kidney, the epididymis, the penis and the pituitary gland.
With whole body autoradiography the tissue distribution was also studied 5 min, 1 hour and 16 hours after an i.v. injection of ¹⁴C-or ³H-labelled SASP in pregnant rats, which had been pretreated orally in 10 days with unlabelled SASP. The aim of this study was to inves tigate whether such a pretreatment caused an altered distribution pattern, compared to that after an i.v. single dose, in the fetal and placental tissues. The fetal concentration did not rise significantly. However, the maternal tissues indicated a slight increase for most tissues.
No changes were found in the excretion of radioactivity or in the metabolite pattern in urine and faeces during the administration. Neither did a consecutive administration of SASP cause any induction of hepatic drug metabolizing enzymes, such as cytochrome P-450, cytochrome b5, aminopyrine demethylase and aniline hydroxylase.

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Salazosulfapyridine(Sulfasalazine, SASP) labelled with ¹⁴C in the carboxyl group and with ³H in the benzenesulfonyl ring was administered intravenously or orally to male and female beagle dogs with and without bile fistulas in order to study the pharmacokinetics. After intravenous administration a plasma elimination half life (t_1/2β) for SASP was calculated to 14 min. The volume of distribution (Vd_ss) was found to be 0.47l/kg and the total clearance was about 35ml/min × kg. After oral administration of 50, 250 or 500mg/kg the time for maximal plasma concentration of SASP was 1 ?? 3 hours and the maximal concentration was 2.81±1.42μM after a dose of 50mg/kg and 15.08±3.04μM after 500mg/kg body weight.
The bioavailability varied between 5.4 ?? 30% which is within the same range as reported from studies in man. The renal clearance was between 0.1 ?? 0.2l/min × kg.
Metabolites of SASP were separated by HPLC and identified by mass spectrometry. 5-aminosalicylic acid (5ASA), sulfapyridine (SP) and its glucuronide were found in plasma and urine. 5ASA, N-acetylated 5ASA (Ac5ASA), SP and unmetabolized SASP were found in faeces.
The cumulative biliary excretion of SASP after i.v. administration was as a mean 95% of the administered dose. Similar figures were obtained for the ¹⁴C and ³H radioactivity. Thus a quantitative excretion of the unchanged drug was found in the bile during 24 hours after administration and >90% was recovered during the first 2hours. No metabolites were found in the bile. After oral administration of SASP 18% of the administered dose was recovered as the unchanged drug in bile, 17% as ¹⁴C and 19% as ³H radioactivity within 48 hours. As after intravenous administration no metabolites were found in bile after the oral administration.
The total recovery of excreted radioactivity after i.v. and oral administration was 69 ?? 96%. The tritium radioactivity representing the SP metabolites was mainly found in urine, while carbon-14 representing SASP and 5ASA metabolites was preferentially excreted in fae ces. This is in accordance with the higher absorption of SP and its metabolites, compared to 5ASA which is poorly absorbed and thus mainly eliminated via faeces together with a small amount of unchanged SASP.

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