Chlorothalonil

Basic toxicokinetics

Administrative data

Endpoint:

basic toxicokinetics in vivo

Type of information:

experimental study

Adequacy of study:

key study

Study period:

12 Oct 2016 to 23 Jan 2017

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Data source

Reference

Reference Type:

study report

Title:

Unnamed

Year:

2017

Report date:

2017

Materials and methods

Objective of study:

absorption

excretion

toxicokinetics

Test guideline

Test guideline 1

Qualifier:

according to guideline

Guideline:

OECD Guideline 417 (Toxicokinetics)

Version / remarks:

2010

Test guideline 2

Qualifier:

according to guideline

Guideline:

EPA OPPTS 870.7485 (Metabolism and Pharmacokinetics)

Version / remarks:

1998

Test guideline 3

Qualifier:

according to guideline

Guideline:

other: EC 1107/2009

Version / remarks:

2009

Test guideline 4

Qualifier:

according to guideline

Guideline:

other: EU 283/2013

Version / remarks:

2013

Test guideline 5

Qualifier:

according to guideline

Guideline:

other: MAFF 12 Nohsan No 8147

Version / remarks:

2000

GLP compliance:

yes (incl. QA statement)

Test material

Test material information

Constituent 1

Reference substance name:

Chlorothalonil

EC Number:

217-588-1

EC Name:

Chlorothalonil

Cas Number:

1897-45-6

Molecular formula:

C8Cl4N2

IUPAC Name:

tetrachlorobenzene-1,3-dicarbonitrile

Radiolabelling:

yes

Test animals

Species:

rat

Strain:

Wistar

Remarks:

Han Wistar

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Age at study initiation: Groups 1& 3: 9-10 weeks; Groups 2 & 4: 8-9 weeks
- Weight at study initiation: 263-298 g for males; 154-190 g for females (Group 1); 236-266 g for males; 158-194 g for females (Group 2); 268-293 g for males; 174-188 g for females (Group 3); 259-298 g for males; 177-200 g for females (Group 4)
- Housing: Pre-study: Multiply housed by sex in solid bottomed polycarbonate cages with bedding. On study: Singly in all-glass metabolism cages (excretion Groups), multiply housed by sex in solid bottomed polycarbonate cages with raised wire mesh floors (kinetic Groups).
- Diet: A standard laboratory diet of known formulation available ad libitum
- Water: tap water ad libitum
- Acclimation period: At least 5 days prior to dosing

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 21 - 22
- Humidity (%): 42 - 58
- Air changes: Minimum of 10/h
- Photoperiod (hrs dark / hrs light): 12/12

IN-LIFE DATES: From: 12 Oct 2016 To: 23 Jan 2017

Administration / exposure

Route of administration:

other: oral gavage and intravenous

Vehicle:

other: Oral: CMC, 0.5% aqueous solution; Intravenous: DMA: 20% Intralipid (5:95)

Details on exposure:

PREPARATION OF DOSING SOLUTIONS:
See "other information on materials and methods incl. tables"

Duration and frequency of treatment / exposure:

Single oral dose administration (Group 1, excretion rats & Group 3, pharmacokinetic rats) or single intravenous dose administration (Group 2, excretion rats & Group 4, pharmacokinetic rats)

Doses / concentrations

Doses / concentrations 1

Dose / conc.:

1.5 mg/kg bw (total dose)

Remarks:

Group 1 & 3: Oral, no-effect dose

Doses / concentrations 2

Dose / conc.:

0.5 mg/kg bw (total dose)

Remarks:

Group 2 & 4: Intravenous, reference route to interpret the level of absorption

No. of animals per sex per dose / concentration:

Four rats per sex per dose group

Control animals:

no

Details on study design:

A group of 4 male and 4 female rats per dose were each given either a single oral administration of nominally 1.5 mg/kg (Group 1, excretion rats & Group 3, pharmacokinetic rats) or a single intravenous administration of 0.5 mg/kg (Group 2, excretion rats & Group 4, pharmacokinetic rats) of [14C]-test substance. In excretion groups excreta samples were taken over predetermined time intervals up to 7 days post dose (Groups 1 and 2). In pharmacokinetic groups blood samples were taken over a 3 day period to determine the pharmacokinetics of total radioactivity in blood.

Details on dosing and sampling:

TOXICOKINETIC / PHARMACOKINETIC STUDY
Excretion: Following dosing, urine and faeces were frozen upon excretion by collection over solid carbon dioxide (up to 168 hours post dose). Urine was collected predose and at 8 hours post dose, faeces was collected at predose, and urine and faeces were then collected at daily intervals until termination (168 hours post dose). The cages were rinsed with ca 5 mL of water prior to the removal of the urine pot. At each urine collection timepoint the cages were rinsed with a suitable volume of water and the washes collected separately. The concentration of total radioactivity was determined in each sample collected.
For rats used to collect excreta, the carcass was retained.

Pharmacokinetics: Blood samples (ca 0.1 mL) were collected from the jugular vein of each rat (into blood tubes containing lithium heparin anticoagulant) at a defined interval over a 72 hour period following dosing. The concentration of total radioactivity was determined in each blood sample collected.

Statistics:

Excretion: calculated mean and standard deviation
Pharmacokinetics: non-compartmental analysis

Results and discussion

Main ADME results

Main ADME results 1

Type:

absorption

Results:

Based on urinary elimination the oral systemically available fraction was 18% in males and 19% in females

Main ADME results 2

Type:

excretion

Results:

after a single oral dose of 1.5 mg/kg - faeces: 81 and 92% of the administered radioactivity in males and females, respectively; - urine: 5.4 and 6.4% of the dose in males and females, respectively; - cage wash: 0.6 and 1.5% for males and females

Main ADME results 3

Type:

excretion

Results:

after a single intravenous dose of 0.5 mg/kg - faeces: 51 and 46% of the administered radioactivity in males and females, respectively; - urine: 36 and 39% of the dose in males and females, respectively; - cage wash: 2.4 and 4.1% for males and females

Toxicokinetic / pharmacokinetic studies

Details on absorption:

Following a single oral and intravenous administration of [14C]-test substance, the data suggest that differences exist between the fate of an intravenous dose and an oral dose. This is demonstrated in the underestimation of oral bioavailability (ca 2%) from the blood data, whereas, at least 5% of the oral dose was excreted in urine. This underestimation could be potentially associated with first pass metabolism, enterohepatic recirculation and/or possibly the reactive nature of the compound in blood and/or tissues.
Consequently, it was evident that the intravenous blood concentrations of radioactivity remained high throughout the study affecting the bioavailability estimate. In addition, at termination there is still ca 11% of the dose remaining in the carcass of the intravenous dose group animals.
The fraction of the oral dose systemically available, estimated by comparing the urinary excretion with that excreted following iv administration, was 18-19% of the administered dose.

Details on excretion:

Single oral dose (1.5 mg/kg bw): The majority of the administered radioactivity was excreted by 24 h post dose (82 and 91% in males and females, respectively). Excretion was essentially complete by 168 h post dose with 0.2% remaining in carcass in both sexes. The total mean recovery of administered radioactivity
including excreta, cage wash and residual carcass was 87 and 100% in male and female rats, respectively.

Single intravenous dose (0.5 mg/kg bw): The majority of the administered radioactivity was excreted by 24 h post dose (72% in both sexes). Excretion was not complete by 168 h post dose with 11-12% remaining in carcass. The total mean recovery of administered radioactivity including excreta, cage wash and residual
carcass was 101 and 102% in male and female rats, respectively.

Toxicokinetic parameters

Toxicokinetic parameters 1

Test no.:

#1

Toxicokinetic parameters:

Cmax: Two hours post dose in males (0.181 µg equiv/g) and 4 hours in females (0.118 µg equiv/g)

Remarks:

Single oral dose of 1.5 mg/kg bw

Toxicokinetic parameters 2

Test no.:

#2

Toxicokinetic parameters:

C(time): C0: 2.43 and 2.56 µg equiv/g, in males and females, respectively

Remarks:

Single intravenous dose of 0.5 mg/kg bw

Metabolite characterisation studies

Metabolites identified:

not measured

Any other information on results incl. tables

Analysis of dose preparation

Prior to dose preparation, the radiochemical was shown to have a purity of >97%. The pre and post-dose radiochemical purity of [14C]-test substance was >96% indicating that the test item was stable during dose preparation and for the duration of the dosing procedure. Analyses of individual aliquots of the oral dose preparation (Groups 1 and 3) prior to dosing were within 5.2% of the mean and therefore dosing proceeded. However analysis of individual aliquots taken throughout the dosing period were within 14.6% of the mean. The individual doses received by these animals were within an acceptable target range to allow the determination of absorption. Analyses of individual aliquots of the intravenous dose preparation (Groups 2 and 4) were within 4.2% of the mean, indicating that a satisfactory homogeneity had been achieved. The group mean achieved oral doses for [14C]-test substance were 1.15 and 1.15 mg/kg (Group 1) and 1.16 and 1.17 mg/kg (Group 3) for males and females. The group mean achieved intravenous doses for [14C]-test substance were 0.469 and 0.443 mg/kg (Group 2) and 0.453 and 0.449 mg/kg (Group 4) for males and females. 

Table 1. Mean Excretion of Radioactivity (as Percentage of Administered Dose) Following a Single Oral (1.5 mg/kg) or Intravenous (0.5 mg/kg) Dose of [14C]-test substance

Time after dosing (h)	Group 1 - 1.5 mg/kg (oral)		Group 2 - 0.5 mg/kg (iv)
	Male (n=4)	Female (n=4)	Male (n=4)	Female (n=3)
Urine
0-8	4.6	4.8	28	29
8-24	0.7	1.4	3.7	5.0
24-48	0.1	0.2	1.9	1.9
48-72	<0.1	<0.1	1.1	1.1
72-96	<0.1	<0.1	0.6	0.7
96-120	<0.1	<0.1	0.4	0.5
120-144	<0.1	<0.1	0.3	0.4
144-168	<0.1	<0.1	0.3	0.3
0-168	5.4	6.4	36	39
0-168 (standardised)A	6.2	6.4	36	38
Faeces
0-24	76	84	39	35
24-48	3.6	6.3	6.4	6.4
48-72	0.5	0.6	2.1	1.9
72-96	0.4	0.5	1.3	1.3
96-120	0.2	0.2	0.9	1.0
120-144	0.1	0.1	0.7	0.8
144-168	<0.1	0.1	0.6	0.5
0-168	81	92	51	46
Cage wash
0-8	0.3	1.1	1.3	2.8
8-24	0.2	0.2	0.3	0.4
24-48	º<0.1	0.1	0.3	0.3
48-72	º<0.1	º<0.1	0.1	0.2
72-96	º<0.1	º<0.1	0.1	0.2
96-120	º<0.1	º<0.1	0.1	0.1
120-144	º<0.1	º<0.1	º0.1	0.1
144-168	º<0.1	º<0.1	0.1	0.2
0-168	0.6	1.5	2.4	4.1
0-168 (standardised)A	0.7	1.5	2.4	4.0
Total excreted	87	100	90	90
% Absorption (urine po/iv)	18	19	-	-
Carcass	º0.2	º0.2	11	12
Total Recovery	87	100	101	102

° = Mean includes results calculated from data less than 30 dpm above background
A = The 0-168 h urine and cage wash data was standardised to a recovery of 100% for the calculation of
absorption from the urinary data.

Table 2. Mean Blood Concentrations and Pharmacokinetic Parameters Following Single Oral or Intravenous Administration of [14C]-test substance to Rats Expressed as µg Equivalents of test substance/g

Nominal Time after dosing (h)	Group 3 – 1.5 mg/kg oral		Group 4 – 0.5 mg/kg iv
	Male	Female	Male	Female
0.25	0.032	0.037	2.049	2.109
0.5	0.055	0.058	1.728	1.745
1	0.094	0.081	1.625	1.601
2	0.181	0.110	1.496	1.515
4	0.128	0.118	1.523	1.451
8	0.068	0.088	1.288	1.322
12	0.059	0.083	1.141	1.150
24	0.040	0.038	1.152	1.077
48	0.028	0.037	0.992	0.988
72	0.021	0.028	0.831	0.790
Cmax (µg equiv/g)	0.181	0.114	-	-
Cmax/D	0.155	0.0983	-	-
C0	-	-	2.43	2.56
tmax (hours)	2	1.5	-	-
t1/2 (hours)	44.8#	52.7#	107#	98.8#
AUC(0-t) (µg equiv.h/g)	3.15	3.50	78.3	76.4
AUC(0-t)/D	2.71	3.01	173	170
AUC(0-inf) (µg equiv.h/g)	4.50#	5.57#	210#	190#
AUC(0-inf)/D	3.84#	4.80#	462#	422#
AUC % Extrap	30.3#	36.8#	61.2#	59.4#
MRT (hours)	22.0	32.4	32.4	32.2
CL (g/h/kg)	-	-	2.28#	2.39#
CLr (g/h/kg)	-	-	2.04	2.18
Vss (g/kg)	-	-	333#	334#
F (%)	1.57	1.77	-	-

PK parameters are Phoenix (WinNonlin) derived. Parameters generated from individual total radioactivity
concentrations.
# = The extrapolation of the AUC to infinity represents more than 20% of the total area.

 

Applicant's summary and conclusion

Conclusions:

Following a single oral administration of [14C]-test substance, the data suggest that differences exist between the fate of an intravenous dose and an oral dose. This is demonstrated in the underestimation of oral bioavailability (ca 2%) from the blood data. This is possibly due to effects of first pass metabolism, enterohepatic recirculation and/or the reactive nature of the test substance in blood and tissues. The fraction of dose systemically available, estimated from the oral:iv urine excretion ratio, was ca 18-19% of the administered dose.

Executive summary:

The excretion and pharmacokinetics of [14C]-test substance was investigated to quantify the absorbed fraction following an oral dose of [14C]-test substance. [14C]-test substance was dosed orally at 1.5 mg/kg and intravenously at 0.5 mg/kg to groups of 4 male and 4 female rats per dose route. Excretion samples were obtained over a 7 day period. After this period, the rats were humanely killed and residual radioactivity was measured in the remaining carcass. Blood samples were taken over a 3 day period to determine the pharmacokinetics of total radioactivity in blood. Male animals had a recovery in the range of 83-88%. Excretion was essentially complete at 168 h post dose with 0.4% or less in the carcass. The low recoveries are likely to be a consequence of the poor homogeneity observed in the dose formulation. This data is accepted and reported throughout. One female animal had a recovery of 87%, the low recovery is likely attributable to a loss of radioactivity from the 8 h urine sample. As this would skew the absorption estimate the animal has been removed from mean calculations. Following a single oral administration of 1.5 mg/kg [14C]-test substance, the majority of administered radioactivity (82-91%) was excreted in the first 24 hours indicating elimination was rapid. The fraction of administered dose systemically available, based on the urinary excretion ratio (oral:iv) accounted for 18-19% of the administered dose. Following a single oral administration of 1.5 mg/kg [14C]-test substance absorption was rapid with peak mean measured blood concentrations observed at 2-4 hours. The oral bioavailability was ca 2% for both sexes suggesting systemic availability was underestimated, as at least 5% of the dose was excreted in urine. No sex related differences were observed in the pharmacokinetics and excretion of total radioactivity. Following a single oral administration of [14C]-test substance, the data suggest that differences exist between the fate of an intravenous dose and an oral dose. This is demonstrated in the underestimation of oral bioavailability (ca 2%) from the blood data. This is possibly due to effects of first pass metabolism, enterohepatic recirculation and/or the reactive nature of the test substance in blood and tissues. The fraction of dose systemically available, estimated from the oral:iv urine excretion ratio, was ca 18-19% of the administered dose.