Methyl (R)-2-(4-(3-chloro-5-trifluoromethyl-2-pyridyloxy)phenoxy)propionate

Basic toxicokinetics

Administrative data

Endpoint:

basic toxicokinetics in vivo

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Data source

Reference

Reference Type:

study report

Title:

Unnamed

Year:

2001

Report date:

2001

Materials and methods

Objective of study:

excretion

metabolism

Test guideline

Test guideline 1

Qualifier:

according to guideline

Guideline:

OECD Guideline 417 (Toxicokinetics)

Deviations:

no

Test guideline 2

Qualifier:

according to guideline

Guideline:

EU Method B.36 (Toxicokinetics)

Deviations:

no

GLP compliance:

yes

Test material

Test material information

Constituent 1

Reference substance name:

Methyl (R)-2-(4-(3-chloro-5-trifluoromethyl-2-pyridyloxy)phenoxy)propionate

EC Number:

406-250-0

EC Name:

Methyl (R)-2-(4-(3-chloro-5-trifluoromethyl-2-pyridyloxy)phenoxy)propionate

Cas Number:

72619-32-0

Molecular formula:

C16H13ClF3NO4

IUPAC Name:

methyl 2-(4-{[3-chloro-5-(trifluoromethyl)pyridin-2-yl]oxy}phenoxy)propanoate

Test material form:

solid

Specific details on test material used for the study:

14C-Labeled R-haloxyfop methyl ester
Lot #: INV 1536
Radiochemical purity: 97.9%
Specific Activity: 18.3 mCi/mmole

Radiolabelling:

yes

Test animals

Species:

rat

Strain:

Fischer 344

Details on species / strain selection:

Fischer 344 rats were selected because of their general acceptance and suitability for toxicity testing, availability of historical background data, and the reliability of the commercial supplier, and the rat is the preferred species for pharmacokinetic/metabolism studies.

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Charles River Laboratories Inc. (Raleigh, North Carolina)
- Age at study initiation: 11 weeks
- Weight at study initiation: Males: 224-234 g and Females: 163-171 g
- Housing: The animals were housed 2 per cage in stainless steel cages
- Diet: PMI® Certified Rodent Lab Diet #5002, ad libitum except that feed was withdrawn from all animals approximately 21-hr prior to the administration of 14C-labeled test substance and returned about 1-hr post-dosing.
- Water: Municipal water, ad libitum
- Acclimation period: 7 days prior to start of the study. Prior to receiving the radiolabeled test substance, the animals were acclimated for four days in metabolism cages.

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 23 ± 1
- Humidity (%): 50 ± 3
- Air changes (per hr): 12-15 times
- Photoperiod (hrs dark / hrs light): 12-hour light/dark

Administration / exposure

Route of administration:

oral: gavage

Vehicle:

corn oil

Details on exposure:

PREPARATION OF DOSING SOLUTIONS: The repeated dose solution was prepared in USP corn oil by the addition of unlabeled test substance. The solution was prepared at a target concentration of 0.05 mg test substance per g. The administration of ~2.2 mL per kg provided a dose level of 0.1 mg/kg. The radio labeled dose solution was prepared in USP corn oil by the addition of 14C-test substance. The solution was prepared at a target concentration of 0.05 mg test substance per g and 2.5 µCi per g. The administration of ~2 g per kg provided a dose level of 0.1 mg/kg and 1 µCi per rat.

Duration and frequency of treatment / exposure:

14 daily oral doses of unlabeled test substance followed on the 15th day oral dose of 14C-labeled test substance

Doses / concentrations

Doses / concentrations 1

Dose / conc.:

0.1 mg/kg bw/day

Remarks:

unlabeled test substance

Doses / concentrations 2

Dose / conc.:

0.1 mg/kg bw/day

Remarks:

14C-labeled test substance

No. of animals per sex per dose / concentration:

4

Control animals:

yes

Details on study design:

- Rationale for animal assignment: Animals were selected from those available using a computer-driven procedure that minimizes the differences between mean body weights within each sex by removing animals at the extremes of body weight range. The animals were identified by a uniquely assigned numbered metal eartag.

Details on dosing and sampling:

TOXICOKINETIC / PHARMACOKINETIC STUDY
- Tissues and body fluids sampled: urine, faeces, blood, plasma, tissues, cage washes
- Time and frequency of sampling: The urine traps were changed at 24-hr intervals for 7 days. The cages were rinsed with water at the time the traps were changed and the rinse collected. Feces were collected in dry-ice chilled containers at 24-hr intervals for 7 days. Seven days after dosing with the 14C-labeled test substance the animals were anaesthetized with CO2 and euthanized by exsanguination via cardiac puncture and tissues were collected. Following the terminal sacrifice of the animals, a final cage wash was performed. Blood was obtained at sacrifice via cardiac puncture. A sample of blood was centrifuged to obtain plasma and plasma analyzed for radioactivity.

Statistics:

Descriptive statistics were used, (i.e., mean ± standard deviation). All calculations were conducted using Microsoft Excel® spreadsheets and databases in full precision mode (15 digits of accuracy). Log-linear regression analysis was used to estimate half-lives of elimination from the urine and feces interval 14C-excretion data.

Samples were considered non-quantifiable if dpm <2x background dpm. For non-quantifiable tissue samples, the quantitation limit (QL) value is displayed as NQ(QL). The mean will be calculated from all actual values and/or calculated QL values and expressed as standard deviation, unless greater than half of the values are presented as NQ, in which case the mean will be expressed as NQ(standard deviation. If all of the values are NQ the mean will be presented as NQ(

Results and discussion

Main ADME results

Main ADME results 1

Type:

excretion

Results:

In total, females eliminated ~96% of the radioactivity while males eliminated ~54% of the radioactivity by 7 days post-dosing.

Main ADME results 2

Type:

distribution

Results:

At sacrifice, males had ~43% of the radioactivity remaining in the carcass and tissues, with ~11% (~0.26 µg-eq/g) found in the liver.

Toxicokinetic / pharmacokinetic studies

Details on distribution in tissues:

Lesser amounts of 14C-activity were found in the carcass and tissues. At sacrifice, males had ~43% of the radioactivity remaining in the carcass and tissues, with ~11% (~0.26 µg-eq/g) found in the liver. Radioactivity in male tissues, in decreasing order of concentration, were liver, kidneys, plasma, whole blood, fat, skin, remaining carcass, and muscle. In females, only small amounts of radioactivity remained in the tissues 7 days post-dosing. The female kidneys, with <1% of the dose administered, had the greatest concentration of radioactivity (~0.02 µg-eq/g), Only small amounts of radioactivity were recovered in the other tissues from females, with muscle, skin, and remaining carcass below the QL of detection.

Comparison of the blood 14C concentration with the plasma 14C concentration suggests that the 14C-test substance-derived radioactivity is primarily distributed to the plasma. The whole blood concentration of radioactivity (0.094 and 0.005 µg eq./g blood, males and females, respectively) was lower than that obtained with plasma (0.151 and 0.007 µg eq./g blood, males and females, respectively). Since red blood cells and plasma are components of whole blood, removal of the red blood cells by centrifugation would have the apparent effect of concentrating the 14C-test substance-derived radioactivity in the plasma.

Details on excretion:

Between 96 and 97% of the administered radioactivity was recovered. Radioactivity was excreted in the feces and urine, although a marked sex difference in the routes and rates of excretion was observed. In total, females eliminated ~96% of the radioactivity while males eliminated ~54% of the radioactivity by 7 days post-dosing.

During the first 24-hr post-dosing with the 14C-test substance, males excreted about 2% and females about 23% of the radio labeled dose in the urine. Through 168-hr post-dosing, males excreted a total of 12.4% of the dose in the urine, whereas females excreted 74.4% of the dose in the urine. A half-life for urinary elimination of 14C-test substance-derived radioactivity was calculated for males and females through 7 days post-dosing as 3.9 ± 0.6 and 1.0 ± 0.0 days, respectively.

Males excreted more of the administered radioactivity in the feces than females. Through 168-hr post-dosing, males excreted about 41.5% of the dose whereas females excreted 21.6% of the dose in the feces. A half-life for fecal elimination of 14C-test substance-derived radioactivity was calculated for each sex. The fecal half-lives of elimination were calculated as 3.9 ± 0.7 days and 1.8 ± 0.3 days for males and females, respectively.

Toxicokinetic parameters

Toxicokinetic parameters 1

Key result

Test no.:

#1

Toxicokinetic parameters:

half-life 1st: The fecal half-lives of elimination were calculated as 3.9 ± 0.7 days and 1.8 ± 0.3 days for males and females, respectively.

Toxicokinetic parameters 2

Key result

Test no.:

#1

Toxicokinetic parameters:

half-life 1st: A half-life for urinary elimination of 14C-test substance-derived radioactivity was calculated for males and females through 7 days post-dosing as 3.9 ± 0.6 and 1.0 ± 0.0 days, respectively.

Metabolite characterisation studies

Metabolites identified:

yes

Remarks:

haloxyfop acid and glucuronide conjugate of haloxyfop acid

Details on metabolites:

No unchanged parent was identified in the urine. The principle radioactive component of male and female urine was identified as haloxyfop acid (8.8% and 67.3% of administered dose for males and females, respectively). One additional metabolite present in female urine at 6.4% of the dose administered was tentatively identified as the glucuronide conjugate of haloxyfop acid.

Unchanged test substance was present at 3.7% and 8.2% of the administered dose in male and female feces, respectively. The principle radioactive component of male and female feces was identified as haloxyfop acid (37.9% and 13.4% of administered dose for males and females, respectively).

Any other information on results incl. tables

Table-1: Distribution of radioactivity 168 hours after oral gavage administration of 14C-test substance to Fischer 344 rats (males)

Sample	Mean ± SD
Urine&Rinse	12.35 ± 1.19
Feces	41.50 ± 3.68
Carcass&Tissues^a	42.58 ± 3.19
Final Cage Wash	0.00 ± 0.00
Total	96.43 ± 4.58

Table-2: Distribution of radioactivity 168 hours after oral gavage administration of 14C-test substance to Fischer 344 rats (females)

Sample	Mean ± SD
Urine & Rinse	74.37 ± 2.62
Feces	21.65 ± 2.83
Carcass & Tissues^a	1.02 ±0.20
Final Cage Wash	0.42 ± 0.85
Total	97.46 ± 1.11

a Liver, skin, whole blood, kidney, muscle, fat and remaining carcass

Table-3: Interval and cumulative excretion in urine of 14C-test substance-derived radioactivity by male and female Fischer 344 rats

Male rats				Female rats
Time (hr)	Sample	Interval	Cumulative	Sample	Interval	Cumulative
0-24	Rinse	0.18 ± 0.05		Rinse	2.03 ± 0.86
	Urine	1.71 ± 0.20		Urine	20.95 ± 9.20
Subtotal		1.89 ± 0.25	1.89 ± 0.25		22.98 ± 9.63	22.98 ± 9.63
24-48	Rinse	0.36 ± 0.15		Rinse	1.71 ± 0.47
	Urine	2.34 ± 0.25		Urine	20.78 ± 2.07
Subtotal		2.70 ± 0.37	4.59 ±0.56		22.50 ± 1.82	45.47 ±11.43
48-72	Rinse	0.17 ± 0.04		Rinse	1.39 ± 1.02
	Urine	1.98 ± 0.01		Urine	12.88 ± 4.11
Subtotal		2.15 ± 0.03	6.74 ± 0.57		14.28 ± 4.99	59.75 ± 6.79
72-96	Rinse	0.24 ± 0.08		Rinse	0.86 ± 0.56
	Urine	1.63 ± 0.17		Urine	7.81 ± 3.56
Subtotal		1.87 ± 0.25	8.61 ± 0.80		8.67 ± 4.05	68.42 ± 3.90
96-120	Rinse	0.16 ± 0.09		Rinse	0.37 ± 0.34
	Urine	1.24 ± 0.14		Urine	3.35 ± 1.80
Subtotal		1.40 ± 0.19	10.00 ± 0.99		3.71 ± 2.12	72.13 ± 2.50
120-144	Rinse	0.25 ± 0.09		Rinse	0.17 ± 0.15
	Urine	0.97 ± 0.08		Urine	1.07 ± 0.44
Subtotal		1.22 ± 0.11	11.22 ± 1.09		1.24 ± 0.54	73.37 ± 2.71
144-168	Rinse	0.20 ± 0.05		Rinse	0.19 ± 0.06
	Urine	0.93 ± 0.13		Urine	0.81 ± 0.13
Subtotal		1.13 ± 0.16	12.35 ± 1.19		1.00 ± 0.11	74.37 ± 2.62
Grand total		12.35 ± 1.19			74.37 ± 2.62

Applicant's summary and conclusion

Conclusions:

Haloxyfop acid was identified in male and female urine (~9% and 67% of administered dose for males and females, respectively) and feces (~38% and 13% of administered dose for males and females, respectively), and male liver and kidney (~11 % and ~2% of dose administered, respectively). The glucuronide conjugate of haloxyfop acid was also identified in female urine (~6% of dose administered). A small amount of test substance was recovered in the feces of both male and female rats (~4% and ~8% of dose administered, respectively).

Executive summary:

The purpose of this study was to provide data on the metabolism and elimination of 14C-test substance following repeated oral gavage administration of test substance to rats. The study was conduted following OECD guideline 417 and EU method B.36. Four male and four female Fischer 344 rats were given 14 daily 0.1 mg/kg oral doses of unlabeled test substance followed on the 15th day by a 0.1 mg/kg oral dose of 14C-Iabeled test substance. The study continued for 7 days following dosing with the 14C-Iabeled test substance.

Between 96 and 97% of the administered radioactivity was recovered. The data indicate that radioactivity derived from the orally administered 14C-R-test substance was efficiently absorbed by both male and female rats with at least 55% and 75%, respectively, of administered radioactivity recovered in the urine, carcass, and tissues. Additionally, 38% and 13% of the dose, males and females, respectively, was recovered in the feces as haloxyfop acid and likely represents absorbed radio labeled material. Therefore, at least 93% and 88% of the administered radioactivity was absorbed in males and females, respectively.

A marked sex difference in the routes and rates of excretion was observed. Through 168 hr post-dosing, males excreted ~12% in the urine, whereas females excreted ~74% in the urine. A half-life for urinary elimination of 14C-test substance-derived radioactivity was calculated for males and females through 7 days post-dosing as 3.9 and 1.0 days, respectively. Males excreted more of the administered radioactivity in the feces than females. Through 168 hr post-dosing, males excreted ~42% whereas females excreted ~22% in the feces. Half-lives for faecal elimination of 14C-test substance-derived radioactivity were calculated for each sex as 3.9 and 1.8 days for males and females, respectively.

At sacrifice, males had ~43% of the radioactivity remaining in the carcass and tissues, with ~11 % (~0.26 µg eq./g) found in the liver. Radioactivity in males tissues, in decreasing order of concentration, were liver, skin, whole blood, kidneys, muscle and fat. In females, only small amounts of radioactivity remained in the tissues 7 days post-dosing. The female liver, with <1% of the dose administered, had the greatest concentration of radioactivity (~0.02 µg eq./g). Only small amounts of radioactivity were recovered in the other tissues from females, with muscle, skin, and remaining carcass below the limit of detection. Pooled samples of male and female urine, faeces, plasma, kidney, and liver were analysed by reversed-phase, high performance, liquid chromatography. There were a total of four radioactive peaks detected in the matrices. No sample contained all four peaks. Based on retention-time comparisons with authentic standards, haloxyfop acid was identified in male and female urine (~9% and 67% of administered dose for males and females, respectively) and feces (~38% and 13% of administered dose for males and females, respectively), and male liver and kidney (~11 % and ~2% of dose administered, respectively). The glucuronide conjugate of haloxyfop acid was also identified in female urine (~6% of dose administered). A small amount of test substance was recovered in the feces of both male and female rats (~4% and ~8% of dose administered, respectively).