1-[(4-chlorophenyl)methyl]-1-cyclopentyl-3-phenylurea

Endpoint summary

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

basic toxicokinetics in vivo

Type of information:

experimental study

Adequacy of study:

supporting study

Study period:

1982-02-03

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

comparable to guideline study with acceptable restrictions

Objective of study:

absorption

distribution

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 417 (Toxicokinetics)

Deviations:

yes

Remarks:

See "Overall remarks" for more information

GLP compliance:

no

Remarks:

Older study, predates mandatory GLP

Radiolabelling:

yes

Species:

other: rat and mouse

Strain:

other: rat: Fisher, and mouse: CD-1 (males only)

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Weight at study initiation:
Rats: ca. 150g (male) and ca. 125 g (female).
Mice (only males): ca. 25 g.
- Diet: ad libitum.
- Water: ad libitum.

ENVIRONMENTAL CONDITIONS
- Temperature: 24±2°C
- Fasting period: 16 hr

Route of administration:

oral: gavage

Vehicle:

other: N,N-dimethylformamide in polyethylene glycol 400 (1:9 v/v)

Details on exposure:

PREPARATION OF DOSING SOLUTIONS:
Phenyl labeled 14C-pencycuron or carbonyl labeled 14C-pencycuron dissolved in 0.5 ml of N,N-dimethylformamide was diluted with 4.5 ml of polyethylene glycol 400 and a 5 ml of mixture solution per kilogram body weight (200 µCi/kg).

Duration and frequency of treatment / exposure:

Single dose

Dose / conc.:

40 mg/kg bw (total dose)

No. of animals per sex per dose / concentration:

3/sex/dose/time point

Control animals:

no

Details on dosing and sampling:

TOXICOKINETIC / PHARMACOKINETIC STUDY (Absorption, distribution)
- Tissues and body fluids sampled:
* Rats: liver, kidney, heart, lung, brain, spleen, pancreas, adrenal, thymus, right femoral muscle, abdominal fat and sexual organs (male: testis, female: uterus and ovary), and blood.
* Mice: blood cell, plasma, liver, kidney, lung, heart, brain, spleen, pancreas, adrenal, gall-bladder, muscle, adipose and testis.

- Time and frequency of sampling:
* Rats: 1, 3, 8, 24, 48, 72 and 144 or 168 hr after the oral administration.
* Mice: 2, 8, 24 and 72 hr after the oral administration.

- Analysis of tissues:
*Rats:
Blood was collected in a 10 ml glass centrifuge tube containing heparin and centrifuged at 2,000 xg for 5 min for separation of plasma and blood cell. The precipitate was washed with 0.9% sodium chloride centrifugally and the washing supernatant was combined with plasma. The total radiocarbon in tissues and blood preparations was analyzed by LSC after the combustion with a sample oxidizer of 100 to 500 mg homogenized tissue sample in triplicate. Digestive organs of stomach, small intestine and large intestine were collected from each animal.

Each digestive organs in rats were homogenized in a Waring blender with five volume of methanol. The methanol extracts after concentration were analyzed directly by Isc and remaining organs samples were analyzed by LSC after oxygen combustion.

*Mice:
The total radiocarbon in tissues of male mice were analyzed by LSC after the combustion with a sample oxidizer of 50 to 400 mg homogenized tissue samples in triplicate.

Type:

distribution

Results:

In rats, excluding the gastro-intestinal tract, concentration of radiolabel at any time-point was highest in the liver. As mice, in contrast to rats, do have a gall-bladder this organ was also included. It
showed by far the highest concentration.

Details on distribution in tissues:

In male rats administered [14C-phenyl]pencycuron, total radiolabel in tissues and organs, excluding the gastro-intestinal tract, peaked three hours after administration at 1.8% of the administered radiolabel. Thereafter, it steadily declined to 0.09% seven days after administration. No such data were presented for other treated groups. No remarkable differences in distribution of radiolabel in male rats were found between administration 14C-phenyl- and 14C-carbonyl labelled pencycuron. For female rats only results of administration of 14C-carbonyl-labelled pencycuron were presented. Both in male and female rats the concentration of radiolabel in tissues and organs, excluding the gastro-intestinal tract, peaked between 3 to 8 hours after administration. Thereafter levels steadily declined. In rats, excluding the gastro-intestinal tract, concentration of radiolabel at any time-point was highest in the liver. For example, three days after administration, concentration of radioactivity in the liver was ca. 1.3 mg eq./kg, while in the other tissue, excluding the gastro-intestinal tract, concentrations were at least 2 times lower. Male mice showed similar patterns after oral administration of 14C-phenyl-labelled pencycuron. As mice, in contrast to rats, do have a gall-bladder this organ was also included. It showed by far the highest concentration of all tissues, with a residual peak 8 h after administration when it was ca. 85 times higher than in the liver.

Metabolites identified:

no

Conclusions:

Administration of carbonyl labeled 14C-pencycuron observed the excretion patterns approximately similar to those obtained with phenyl labeled chemical. Significant difference in the residual concentration of radiocarbon was not observed between male and female rats. No accumulation of 14C-pencycuron in the specific tissues of rat and mouse were presumed.

Executive summary:

Male and female rats and male mice were administered orally with phenyl labeled ¹⁴C-pencycuron [1-(p chlorobenzyl)-1-cyclopentyl-3-phenyl urea] at the dosage level of 40 mg/Kg and the absorption, the distribution and the residue levels in the tissues and organs studied. The administered ¹⁴C-pencycuron was readily absorbed and distributed into various tissues. The radiocarbon in tissues was found shortly after the administration; liver, kidney, lung, adrenal and adipose contain large amount of radiocarbon, while brain, muscle and testis might contain less amount of radiocarbon. The half lives of animal body were in order of 13-27 hr (rat) and 6-16 hr (mouse). In addition, administration of carbonyl labeled ¹⁴C-pencycuron observed the excretion patterns approximately similar to those obtained with phenyl labeled chemical. Significant difference in the residual concentration of radiocarbon was not observed between male and female rats. No accumulation of ¹⁴C-pencycuron in the specific tissues of rat and mouse were presumed. The high residue concentration observed in the gall-bladder of mouse was suggested to be due to active biliary excretion.

Reference 2

Endpoint:

basic toxicokinetics in vivo

Type of information:

experimental study

Adequacy of study:

supporting study

Study period:

1982-02-10

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

comparable to guideline study with acceptable restrictions

Objective of study:

absorption

excretion

metabolism

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 417 (Toxicokinetics)

Deviations:

yes

Remarks:

partly in accordance with OECD 417. See "Overall remarks" for more information

GLP compliance:

no

Remarks:

Older study, predates mandatory GLP

Radiolabelling:

yes

Species:

rat

Strain:

Fischer 344

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Age at study initiation: 8 week.
- Housing: Immediately after administration, each rat was individually housed in all glass metabolism cage.

ENVIRONMENTAL CONDITIONS
- Fasting period: 16 hr before the administration.

Route of administration:

other: Oral:gavage (single dose) and intraperitoneally (males only, for the study on absorption of pencycuron)

Vehicle:

other: N,N-dimethylformamide in polyethylene glycol 400 (1:9 v/v)

Details on exposure:

PREPARATION OF DOSING SOLUTIONS:
Phenyl labeled 14C- and carbonyl labeled 14C-pencycuron were dissolved in 0.5 ml of N,N dimethylformamide was diluted with 4.5 ml of polyethylene glycol 400 and a 5 ml of the mixture solution per kilogram body weight (200 µCi/kg) was orally administered to the rats through stomach tube at the dose of 40 mg/kg and 200 mg/kg as a single dose.

For the study on absorption of pencycuron, male rats were treated intraperitoneally with 40 mg/kg of phenyl labeled 14C-pencycuron (200 µCi/kg) suspended in Emulgator W. Please note that the i.p. dosed males received phenyl-labelled, not carbonyl-labelled pencycuron.

Duration and frequency of treatment / exposure:

Single dose

Dose / conc.:

40 mg/kg bw (total dose)

Remarks:

i.p. ([14C-phenyl]pencycuron only)

Dose / conc.:

40 mg/kg bw (total dose)

Remarks:

Single oral low dose

Dose / conc.:

200 mg/kg bw (total dose)

Remarks:

Single oral high dose

No. of animals per sex per dose / concentration:

3/sex/dose

Details on dosing and sampling:

METABOLITE CHARACTERISATION STUDIES
- Tissues and body fluids sampled: urine, faeces and expired air.
- Time and frequency of sampling: Urine and faeces were collected daily for up to 7 days for the low dose and 4 days for the high dose groups. The first 48 h the expired air of the male rats dosed with 40 mg/kg bw was trapped to be analysed for 14CO2.
- Method type(s) for identification: LSC, TLC and autoradiography:
The 0-3 days urine and faeces collections were extracted with, respectively, chloroform, and methanol and chloroform. The chloroform extracts were analysed using TLC and autoradiography. The aqueous phases were analysed for conjugates using glucuronidase, glucuronidasearylsulfatase and D-saccharic acid 1,4-lactone. All urine and faeces samples, extracts and fractions were analysed for radiolabel with (combustion) LSC.

Type:

absorption

Results:

Oral absorption was 30-53% based on urinary excretion, varying with sex and radiolabel site

Type:

metabolism

Results:

The aqueous fraction of the chloroform-extracted urine of males dosed with 40 mg/kg bw contained mainly sulfate-conjugates, both after oral administration of carbonyl- and phenyl-labelled pencycuron.

Type:

excretion

Results:

Approximately four days after oral administration of 40 mg/kg bw, cumulative excretion did not increase anymore during the next three days it was followed.

Details on absorption:

Oral absorption in males, seven days after administration of 14C-carbonyl- or 14C-phenyl-labelled pencycuron, was at least ca. 30% of the administered radiolabel, based on radiolabel recovered from urine. For females dosed with 40 mg/kg bw pencycuron, oral absorption was at least 35%, based on 14C-carbonyl-radiolabel recovered from urine, while based on 14C-phenyl-radiolabel recovered from urine, absorption was at least 53%. After single oral high dose (200 mg/kg bw), more radiolabel was excreted in faeces than after the lower dose. This effect was more pronounced with the 14C-carbonyl label. This indicates absorption and/or metabolic pathways may have become saturated. Oral absorption, based on radiolabel recovered from urine, was 19-13% (m-f) of the administered dose for the 14C-carbonyl and 28-37% for 14C-phenyl label.

Details on excretion:

The radiocarbon expired by male rats dosed with 40 mg/kg bw represented less than 0.1% of the administered radiolabel. Approximately four days after oral administration of 40 mg/kg bw, cumulative excretion did not increase anymore during the next three days it was followed. Judging by the time course of cumulative excretion in the high dose groups (200 mg/kg bw/d), at least in faeces cumulative excretion could have increased more, four days after administration. However, in these dose groups excretion was no longer monitored after this time-point.

Metabolites identified:

yes

Details on metabolites:

Based on the different balance between males and females in urinary and faecal excretion after administration of 14C-phenyl labelled pencycuron and on a different distribution of radiolabel over the various urinary and faecal metabolite fractions after oral administration of either label, quantitative metabolic differences between male and female rats seem to exist. The aqueous fraction of the chloroform-extracted urine of males dosed with 40 mg/kg bw contained mainly sulfate-conjugates, both after oral administration of carbonyl- and phenyl-labelled pencycuron. The aqueous fraction represented ca. 20% of the administered dose.

Table 1: Radiolabel recovered from urine and faeces of rats exposed to 14C-labelled pencycuron

Label	^14C-carbonyl		^14C-phenyl
Collection period (h)	168	96	168	168	96
Dose (mg/kg bw)	40 p.o. m-f	200 p.o. m-f	40 p.o. m-f	40 p.o. m	200 p.o. m-f
Urine	30-35	19-13	31-53	30	28-37
Faeces	64-62	71-83	71-49	59	66-60
Recovery	94-97	90-96	102-102	89	94-97

Conclusions:

Pencycuron administered orally into the stomach is quickly absorbed from the small intestine, distributed in whole body, and then metabolized and excreted mainly in feces and urine. Although administration method was different in oral and intraperitoneal, most of administered radiocarbon was recovered from the feces and the elimination patterns were observed approximately similar. This suggests that the biliary excretion was the important excretion pathway at the metabolism of pencycuron in rat. On the other hand, the most of urinary radioactive materials were present as sulfate conjugates.

Executive summary:

Phenyl and carbonyl labeled 14C-pencycuron [1-(p-chlorobenzyl)-1-cyclopentyl-3-phenylurea] was administered orally to male and female rats at the dosage level of 40 mg/kg and 200 mg/kg. The applied radiocarbons were rapidly and almost completely recovered from excreta of male and female rats at both dose level during the experimental period.

 

Following administration with either [phenyl-14C]- or [carbonyl-14C]- pencycuron, males excreted 30% of the dose in the urine and 65% in the feces, and females excreted 30 to 48% in the urine and 45% in the feces within 3 days. Expired radiocarbon was less than 0.1% of the dosage at the case of male rats. When male rats were administered intraperitoneally with 40 mg/kg of phenyl labeled 14C-pencycuron, most of the applied radiocarbon was recovered in feces and the elimination patterns were similar to that of oral administration.

This suggests that the biliary excretion was the important excretion pathway for the metabolism of pencycuron in rat. The radiocarbon excreted in feces was mainly recovered in chloroform extract fraction, and only trivial percentage of conjugated materials were present in feces. On the other hand, the most of urinary radioactive materials were present as sulfate conjugates.

Reference 3

Endpoint:

basic toxicokinetics in vivo

Type of information:

experimental study

Adequacy of study:

supporting study

Study period:

1989-12-20 to 1991-04-11

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

comparable to guideline study

Objective of study:

absorption

distribution

excretion

metabolism

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 417 (Toxicokinetics)

Deviations:

yes

Remarks:

See "Overall remarks" for more information

GLP compliance:

yes (incl. QA statement)

Radiolabelling:

yes

Remarks:

Both radiolabeled ([N-14C-methyl]pencycuron) and non-radiolabeled test materials were used.

Species:

rat

Strain:

Wistar

Remarks:

SPF Cpb

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Weight at study initiation: Approximately 200 g.
- Housing: During the excretion studies the animals were kept in special metabolism-cages, which allowed for a separate and quantitative sampling of the excreta. In all other cases animals were kept in plastic cages on wood shavings. During the non-radioactive pretreatment period the rats were housed as single animals in plastic cages.
- Acclimation period: 7 days

ENVIRONMENTAL CONDITIONS
- Temperature: The animals were kept at room temperature during the test period of 48 hours. In the non-radioactive pretreatment period and during the bile fistulation the rats were housed under controlled temperature (20°C).
- Humidity: In the non-radioactive pretreatment period and during the bile fistulation the rats were housed under controlled humidity (40-80 %) conditions.

Route of administration:

other: Oral:gavage or intraduodenally (bile cannulated animals)

Vehicle:

other: 0.5% Tragacanth suspension

Details on exposure:

PREPARATION OF DOSING SOLUTIONS:
The radiolabelled compound was shipped as a solid substance and stored as such in a refrigerator. For the preparation of the administration solution the appropriate amounts of labelled and non-labelled compound were homogeneously mixed in a 0.5 % Tragacanth™ suspension using an ultrasonic water bath at 70°C.

Duration and frequency of treatment / exposure:

Rats were administered single low or high doses of radiolabelled pencycuron; or a single low dose of radiolabelled pencycuron following 14 consecutive daily doses of unlabelled pencycuron.

Dose / conc.:

2 mg/kg bw/day

Remarks:

Repeated oral low dose (non radioactive doses)

Dose / conc.:

2 mg/kg bw/day

Remarks:

Single oral low dose

Dose / conc.:

100 mg/kg bw/day

Remarks:

Single oral high dose

No. of animals per sex per dose / concentration:

5/sex/dose regimen (intact animals).
6/dose (bile cannulated animals).

Control animals:

no

Details on study design:

Rats were administered single low or high doses of radiolabelled pencycuron; or a single low dose of radiolabelled pencycuron following 14 consecutive daily doses of unlabelled pencycuron. An additional group of bile cannulated males was included in the experiment, which received a single low dose, administered intraduodenally. In a separate experiment with 5 orally dosed males (single, 100 mg/kg bw) expired CO2 was trapped. Urine, faeces, and carbon dioxide were collected separately for each animal. The collection intervals for intact animals were 0-4, 4-8, 8-24, 24-32, 32-48, 48-56 and 56-72 h for urine, 0-24, 24 48 and 48-72 h for faeces and 0-8, 8-24 and 24-48 h for CO2. In the bile-cannulation experiment, bile and urine were collected and assayed for radioactivity each hour for the first 4 hours, subsequently at 6, 8 and 12 h, and thereafter each 6 hours until the termination of the experiment, 48 h after dose administration. The collection intervals for faeces were 0-24 and 24 48 h. Plasma from intact animals was sampled after progressively longer intervals during the whole test period. Toxicokinetic parameters were computed using the so-called model-free calculation. The intact animals were sacrificed three days after dose administration, and the bile cannulated ones two days after dose administration. After sacrifice, tissues and organs were removed from the intact animals for weighing and radiometry. From the bile cannulated animals only, the gastrointestinal tract was removed. All excreta, tissues, organs, and residual carcasses were analysed for radioactivity by (combustion) LSC.

Metabolites from urine and faeces samples were purified, identified, and quantified by methanol and acetonitril extraction, micropreparative HPLC, analytical HPLC, GC/MS and NMR. Arylsulfatase and glucuronidase incubations were used to identify conjugated metabolites.

Details on dosing and sampling:

The administered volume was 10 ml/kg body weight for oral and 1 ml/kg for intraduodenal administration. The administration was carried out immediately after the preparation of the solution; during the period of non-radioactive pretreatment the solution for the administration on the weekends was prepared on the preceding Friday afternoon.

Animal groups:
Dose group B: single oral low dose (2 mg/kg bw); male rats, test no 1; female rats, test no 2;
Dose group C: 14 daily single oral low non radioactive doses (2 mg/kg bw), followed by a single oral low radioactive dose after 24 h; male rats, test no 3; female rats, test no 4;
Dose group D: single oral high dose (100 mg/kg bw); male rats, test no 5; female rats, test no 6;

Bile Study: bile fistulated male rats, intraduodenal single low dose (2 mg/kg); test no 8.

Statistics:

Values identified as outliers were marked and not taken into account in calculations of arithmetic means and standard deviations. Characteristic values for the evaluation of the biokinetic behaviour based on the excretion or residue data from the different animal groups were checked for statistically significant differences using the non-parametric MANN-WHITNEY-U-test. The following levels of significance were specified:

< 95% = not significant
> 95% = probably significant
> 99% = significant

Type:

absorption

Results:

oral absorption of pencycuron into systemic circulation is at least 7.0% (referring to dose applied) after single low dose, at least 11% after repeated low dose and at least 4.0% after single high dose, 72 h after dose administration.

Type:

distribution

Results:

The amount retained in the body, three days after administration, was relatively small for all dose groups, no evidence of accumulation.
In all cases the concentration of radioactivity was highest in the liver, three days after administration.

Type:

metabolism

Results:

Pencycuron was extensively metabolised once absorbed (virtually no parent compound detected in urine).

Type:

excretion

Results:

Within 24 h 76-83% of the administered dose (males-females), after repeated low dose, mainly via faeces (ca. 80% or more of total excretion)within 72 h 76-91% of the administered dose (males-females), mainly via faeces (ca. 80% or more of total excretion)

Details on absorption:

Relative absorption three days after dose administration seems to be somewhat higher in females than in males, after low dose administration (both single and repeated). However, this may be an artefact of the lower recovery of radiolabel in the latter sex. Based on the radiolabel recovered from urine, and body (minus GIT), oral absorption of pencycuron into systemic circulation is at least 7.0% (referring to dose applied) after single low dose, at least 11% after repeated low dose and at least 4.0% after single high dose, 72 h after dose administration. Within 48 hours after administration, absorption from the gut (ca. 46%), after single low dose administration, is considerably higher, based on radiolabel recovered from urine, bile, and body (minus GIT).

Details on distribution in tissues:

The amount retained in the body, three days after administration, was relatively small for all dose groups: 0.22% of the administered dose or less. In all cases the concentration of radioactivity was highest in the liver, three days after administration, with one notable exception: in the males of the single low dose group the concentration in bone was even somewhat higher. However, this is probably an artefact, as in all other dose groups no significant differences were found between males and females and in this case the concentration in males is approximately 8x higher than in females.

Concentrations in the liver were 0.030-0.024 mg eq./kg (m-f) after single low dose, 0.041-0.041 mg eq./kg after repeated low dose and 0.14-0.092 mg eq./kg after single high dose. In all other tissues (with the exception mentioned above) concentrations were a factor 3 or more lower. It is furthermore noted that in all dose groups the concentration of radioactivity was a factor 6-15 higher in erythrocytes than in plasma.

After high dose administration the relative AUC* is lower than after repeated or single low dose, indicating that absorption is saturated at high dose (see Table 3). The high distribution volumes observed at all dose regimens, illustrate that, once in plasma, radiolabel from pencycuron is rapidly distributed.

* The concentration (per kg tissue) in the toxicokinetic calculations was expressed relative to the dose administered (per kg bw). Consequently, also the AUC derived from the concentration versus time curve is a value relative to the dose administered, and not an absolute figure.

Details on excretion:

In high dose males, less than 0.03% of the administered radiolabel was excreted as CO2 and can be considered negligible. In all dose groups, most radiolabel was excreted in faeces (65 to 82% of the administered radiolabel), 72 h after administration. The percentage faecal excretion was higher after single high dose than after single low dose, indicating that the process may have been saturated at high dose. Both in males and females, repeated low dose led to a somewhat increased urinary excretion compared to single low dose, which may indicate enzyme induction by repeated dosing.

Three days after administration, excretion in urine was at least 7.0% after single low dose, at least 11% after repeated low dose and at least 4.0% after single high dose. Total excretion within three days after administration was 84-92% of the administered dose (m-f) after single low dose, 76-91% after repeated low dose and 86-85% after single high dose. For all dose regimens excretion is nearly completed in the first 24 h, as more than 90% of the amount excreted within three days had been eliminated in that period.

The bile cannulation experiment executed with males administered a single low dose, demonstrates a sizeable first pass effect, as approximately 42% of the administered radiolabel is excreted in bile within 48 h of administration (see table 2). Biliary excretion is relatively rapid, as 12 h after administration more than 90% of the biliary excretion recorded over two days has taken place. At least some enterohepatic circulation took place, as in the same time span (48 h) urinary excretion in intact males (single low dose) was approximately twice as high as in their bile cannulated counterparts (2.9 and 6.9% of the administered dose, respectively). However, still most of the biliary radiolabel appears to (eventually) end up in the faeces, as 48 h after administration faecal radiolabel is 1.5 times higher in intact males than in their bile cannulated counterparts.

Metabolites identified:

yes

Details on metabolites:

In all dose groups, most of the radioactivity recovered from faeces was present as unaltered pencycuron, while the most prominent metabolite was THS1787 (= M16 = PB-amine; 8-10% of the recovered radiolabel in all dose groups). The other identified metabolites were M941 (= M07 trans), M942 (= M07 cis), M932 (= M08) and M929 (= M05) each accounting for 1-4% of the recovered radiolabel after low dose (single or repeated) and for 0.4-1% after single high dose. After high dose more unchanged pencycuron (70-78% of the recovered radiolabel) was observed in faeces than after single low dose (52-45%), most likely because the absorption process was saturated. After repeated low dose less unchanged pencycuron (42-35%) was found than after single low dose (52-45%), another indication of enzyme induction after repeated administration. The most prominent metabolites identified in urine were 4-chlorohippuric acid (= M12) , accounting for 0.9-4.0% of the recovered radiolabel and the glucuronide of M932 (= M08) (0.5-3.7%). Other metabolites identified in urine were ECW6462 (= M05-glcm) and M932 (= M08), each accounting for less than 1% of the recovered radiolabel, and the glucuronide of M929 (= M05) (not quantified). No unchanged pencycuron was found in urine. Between 70 and 92% of the radiolabel recovered in the various dose groups was identified.

Cumulative excretion and retention in rats of total radioactivity, 24 and 72 h after oral exposure to pencycuron

Excretion and retention are expressed as percentage of the administered radiolabel.

	0-24 h			0-72 h
	Dose group			Dose group
Fraction	single oral low m-f	repeated oral low m-f	single oral high m-f	single oral low m-f	repeated oral low m-f	single oral high m-f
Urine	6.4-12	10-17	3.6-3.6	7.0-14	11-19	4.0-4.4
Faeces	74-74	62-66	81-78	77-78	65-72	82-81
Total excreted	80-86	72-83	84-82	84-92	76-91	86-85
GIT	NC	NC	NC	0.02-0.02	0.02-0.03	0.009-0.01
Body-GIT	NC	NC	NC	0.10-0.11	0.22-0.12	0.056-0.034
Total recovered	80-86	72-83	84-82	84-92	76-91	86-85

GIT = gastro-intestinal tract, NC = not collected/determined

 

Cumulative excretion and retention of total radioactivity in male rats with cannulated bile ducts, 12 and 48 h after single intraduodenal administration of 2.0 mg pencycuron/kg bw

Excretion and retention are expressed as percentage of the administered radiolabel.

Fraction	0-12 h	0-48 h
Urine	2.9	3.8
Faeces	NC	50
Bile	39	42
Total excreted	42	96
GIT	NC	0.008
Body-GIT	NC	0.09
Total recovered	42	96

NC = not collected/determined

 

Some toxicokinetic parameters from plasma curve analysis

Parameter	Dose
	single oral low m-f	repeated oral low m-f	single oral high m-f
Area under the curve: AUC (h)	0.63-1.3	0.75-1.3	0.41-0.60
Steady distribution volume: VSS (L/kg)	20-8.1	9.0-7.2	32-30
Clearance: CL (mL/min)	2.6-1.2	2.1-1.2	4.2-2.7
Renal clearance: CLr (mL/min)	0.49-0.40	0.68-0.56	0.43-0.34
Terminal elimination half-life: t1/2 (h)	38-38	27-43	31-41

Conclusions:

The oral absorption of pencycuron in the rat was estimated to be 46% based on findings from bile duct cannulated rats. Absorbed pencycuron was distributed with no evidence of accumulation, and was extensively metabolized. The majority of pencycuron is excreted in faeces.

Executive summary:

[4-chlorobenzyl-a-uC]Pencycuron was administered orally to three groups of 5 rats, each, of either sex at different dosing levels or dosing conditions according to the "EPA Pesticide Assessment Guidelines" to study absorption, distribution, excretion and biotransformation in dependence on dose, pretreatment and sex. Animals with bile fistulae were dosed to collect bile fluid to study absorption after oral administration. The following results were obtained:

 

At the low dose level, 46% of the dose administered to bile fistulated animals was absorbed; absorption started immediately after administration, reaching the peak plasma level of less than 0.2 Mg/ml after 4 h. These results indicate, that pencycuron is poorly absorbed, but the absorbed part is readily distributed into peripheral compartments. Under steady state conditions the radioactivity permeates readily into the tissues and, with a low mean residence time, back into the plasma prior to elimination mainly via the bile.

 

Recoveries of radioactivity were found to be 84% to 91% except for the pretreated male animal group with 75% recovery; for better comparison the percent values in the report presented were normalized for recovered radioactivity values.

 

Biotransformation to volatile metabolites (including carbon dioxide) was negligible («0.1%); 99% of the recovered radioactivity was excreted within 72 h after oral administration. The major route of elimination was via the faeces, with the high dose animals showing approximately 95% and the low dose animals 85% to 92% of the recovered radioactivity in the faeces.

 

The radioactivity remaining in the body excluding the gastrointestinal tract at sacrifice (72 h after administration) was in all cases tested «1% of the recovered radioactivity. From the kinetic data it can be extrapolated that this radioactivity is subject to further elimination from the body.

 

The different test conditions resulted in the following effects:

- Male rats treated with the low dose with or without non-radioactive pretreatment (Tests 1 and 3) exhibited higher values for total and renal clearance leading to a faster elimination of radioactivity from the plasma than female rats.

- Dose dependence was found in the ratio of elimination with urine and faeces: rats treated with the high dose of 100 mg/kg showed a substantially lower renal and a correspondingly higher faecal elimination than those at the low dose level (2 mg/kg). The higher faecal elimination was accompanied by a much higher percentage of unchanged parent compound (70% - 78%) as compared to the low dose level values (45% - 52%).

- Pretreatment of the animals for 2 weeks with the non-labelled test compound increased the renal elimination rate pointing to a higher degree of biotransformation to polar metabolites; this finding was confirmed in the analytic part of the study where higher amounts of hydroxylated metabolites and a slightly lower extractability of radioactivity from faeces were found.

 

Nine different metabolites of pencycuron were identified by NMR and MS spectroscopic techniques; the non conjugated metabolites were additionally identified by cochromatography with authentic reference compounds in at least two different chromatographic systems with coupled UV and radioactivity detection. Beside parent compound which was the main radioactive component in faeces, the major biotransformation product was the 4-chlorobenzyl-cyclopentylamine, found exclusively in faeces, followed by the 4-chlorohippuric acid in urine.

 

The hydroxylated metabolites with at least one hydroxy-function in the 4-position of the aniline moiety of the molecule were found unconjugated in the faeces and mostly conjugated in urine. None of these hydroxylated metabolites amounted to more than 4% of the recovered radioactivity.

 

The identification rate was mainly dependent on the dose group and to a minor extent on sex; the metabolites in the excreta of the low dose animals (Tests 1 and 2) were identified to 71% (males) and 73%, in the pretreated low dose group to 62% and 64% and in the high dose group to 85% and 92%; in all dose groups the identification of metabolites amounted to roughly 20% (males) to 30% above the level of the unchanged test compound in the excreta.

 

Pretreatment of the animals seemed to induce metabolism to more polar metabolites, which were prone to renal elimination and to tighter binding to formed particles in faeces, unextractable with the methods used.

 

With the results presented, the metabolic behaviour of [4-chlorobenzyl-a-14C]pencycuron in rats concerning rate and amount of absorption, distribution, excretion, and biotransformation seem to be sufficiently understood. A biotransformation pathway is established including all the metabolites identified.

Description of key information

Three studies are available, which investigate the absorption, distribution, metabolism and excretion of radiolabellled pencycuron in the rat following oral administration.

Rate and extent of absorption

Absorption from the gut after single oral low dose was 46% within 48 hours of dosing, based on radiolabel recovered from bile, urine, tissues and organs.  The EFSA Conclusion reports a dermal absorption value of 0.2% for pencycuron from a formulated product.  In the absence of data, inhalation absorption is assumed to be twice the level of oral absorption.

Distribution

72 hours after administration, tissue residues were highest in the liver reflecting biliary excretion.

Potential for accumulation

There is no evidence of accumulation

Rate and extent of excretion

Within 24 hours, 76-83% of the administered dose was excreted (males-females).  After repeated low doses, excretion was mainly via faeces (80% or more of total excretion).  Within 72 hours, a total of 76-91% of the administered dose (males-females) was excreted, mainly via faeces (80% or more of total excretion).

Metabolism

Absorbed pencycuron was extensively metabolised once absorbed: virtually no parent compound was detected in urine.

Test Species/Type	Results	Assessment	Reference
OECD 417 - ADME study in the rat with radiolabelled pencycuron: single low, high and repeated low dose	Absorption was incomplete, with the majority of absorbed radiolabel excreted in bile.  Absorption was higher follwoing repeated dosing and was saturated at a high dose level.  A high proportion of the adminstered radiolabel was excreted unchanged in the faeces.  Absorbed radioactivity was rapidly distributed and excreted largely within 24 hours.  4-chlorohippuric acid was identified as the major urinary metabolite.	Supporting study	Ecker, et al.  (1989)
OECD 417 (partially) - Metabolism study in the rat, with radiolabelled pencycuron (two different label sites)	Oral absorption was 30-53% based on urinary excretion, varying with sex and radiolabel site	Supporting study	Oyama, et al (1982)
OECD 417 (partially) - Tissue distribution study in rats and mice with radiolabelled pencycuron (two different label sites)	Tissue levels of radioactivity were highest in the liver, gastrointestinal tract and (in the mouse) gall bladder.  Tissue levels peaked relatively quickly after dosing and declined thereafter.	Supporting study	Kobori, et al (1982)

Key value for chemical safety assessment

Bioaccumulation potential:

no bioaccumulation potential

Absorption rate - oral (%):

46

Absorption rate - dermal (%):

0.2

Absorption rate - inhalation (%):

100