2-hydroxypropyl [(1R,2S,5R)-2-isopropyl-5-methyl-cyclohexyl] carbonate

Endpoint summary

Description of key information

NOAEL (28 days, rat, oral) = 150 mg/kg bw/day (subacute)(OECD 407; GLP compliant)

Key value for chemical safety assessment

Repeated dose toxicity: via oral route - systemic effects

Link to relevant study records

Reference

Endpoint:

short-term repeated dose toxicity: oral

Type of information:

experimental study

Adequacy of study:

key study

Study period:

1994-01-25 to 1994-07-06

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 407 (Repeated Dose 28-Day Oral Toxicity Study in Rodents)

Version / remarks:

1981-05-12

Deviations:

no

Qualifier:

according to guideline

Guideline:

EU Method B.7 (Repeated Dose (28 Days) Toxicity (Oral))

Version / remarks:

1992

GLP compliance:

yes (incl. QA statement)

Remarks:

signed 1994-03-16

Limit test:

no

Species:

rat

Strain:

Sprague-Dawley

Remarks:

CD

Details on species / strain selection:

The rat was selected for this study as it is a readily available rodent species historically used in safety evaluation studies and is acceptable to appropriate regulatory authorities.

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Charles River (U.K.) Limited, Manston, Kent
- Age at start of treatment: approx. six to seven weeks old
- Weight at start of treatment: males: 183 g to 230 g; females: 159 g to 191 g
- Housing: housed in groups of five by sex in polypropylene grid-floor cages suspended over trays lined with absorbent paper.
- Diet (ad libitum): pelleted diet (Rat and Mouse SQC Expanded Diet No. 1)
- Water (ad libitum): mains water
- Acclimation period: fourteen days

DETAILS OF FOOD AND WATER QUALITY:
The diet and drinking water were considered not to contain any contaminant at a level that might have affected the purpose or integrity of the study.

ENVIRONMENTAL CONDITIONS
- Temperature: 20 - 23 °C
- Relative humidity: 28 - 69 %.
- Air changes: at least fifteen air changes/hour
- Photoperiod (hrs dark / hrs light): 12/12

Route of administration:

oral: gavage

Details on route of administration:

The oral route was selected by the study sponsor as a possible route of human exposure and the results of the study are believed to be of value in predicting the likely toxicity of the test material to man.

Vehicle:

arachis oil

Remarks:

B.P. (British Pharmacopoeias)

Details on oral exposure:

PREPARATION OF DOSING SOLUTIONS:
The test material was prepared at the appropriate concentrations as a solution in the vehicle. Formulations were prepared weekly and stored at 4°C in the dark.
The volume of test and control material administered to each animal was based on the most recent bodyweight and was adjusted at weekly intervals.

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

The stability, homogeneity, and concentration of the test material formulations were analysed. The test item concentration in the test samples was determined by gas chromatography using an external standard technique.
For homogeneity determination, the test material formulations were mixed thoroughly and samples were taken from the top, middle and bottom of the container shaking in between sampling. The sampling was performed in triplicate.
For stability determination, the test material formulations were sampled and analysed initially and then after stroage at approximately 4 °C in the dark for ten days.
For the verification of the test material formulation concentration, the test material formulations were sampled and analysed within three days of preparation.
Results:
The formulation showed to be stable for at least ten days. In addition the results indicated that the prepared formulations were within ± 11 % of the nominal concentration.

Duration of treatment / exposure:

28 consecutive days

Frequency of treatment:

daily

Dose / conc.:

15 mg/kg bw/day (actual dose received)

Dose / conc.:

150 mg/kg bw/day (actual dose received)

Dose / conc.:

1 000 mg/kg bw/day (actual dose received)

No. of animals per sex per dose:

Main groups: 5 males / 5 females
Recovery groups (vehicle control recovery and 1000 mg/kg bw/day recovery group): 5 males / 5 females

Control animals:

yes, concurrent vehicle

Details on study design:

- Dose selection rationale:
The dose levels for the 28-day repeated dose toxicity study were chosen based on the results of a range-finding study. In the range finding study groups of 3 male and 3 female Sprague-Dawley CD strain rats were dosed with either 150, 400, or 1000 mg/kg bw/day of the test item in arachis oil B.P. by gavage for a duration of 14 consecutive days. A vehicle control group was run concurrently. The following parameters were examined/recorded: clinical signs, mortality, body weight, and gross pathology.
Results:
Mortality:
There were no deaths during the study.

Clinical signs:
150, 400. or 1000 mg/kg bw/day: animals treated with the test material showed short-lived increased salivation immediately after dosing from Day 3 onwards.
1000 mg/kg bw/day: isolated incidents of more prolonged increased salivation were observed from Day 9. Associated findings of fur wetting and/or red/brown staining around the mouth were also observed on isolated occasions during the study.
400 mg/kg bw/day: one animal showed red/brown staining around the mouth

Body weight:
Animals treated with the test material showed similar body weight gains to controls during the study.

Gross pathology:
No macroscopic abnormalities were seen at terminal kill.

The dose levels for the main twenty-eight day study were chosen, following consultation with the sponsor, as: 15, 150, and 1000 mg/kg bw/day plus a control group treated with vehicle only.

- Post-exposure recovery period in satellite groups: 14 days

Positive control:

no data

Observations and examinations performed and frequency:

CAGE SIDE OBSERVATIONS: Yes
- Time schedule (treatment period): immediately before dosing and one and five hours after dosing during the working week or immediately before dosing and one hour after dosing at weekends.
- Time schedule (treatment-free period): twice daily, morning and afternoon (once daily at weekends and on public holidays).
- Cage side observations checked: overt signs of toxicity, ill-health or behavioural change

DETAILED CLINICAL OBSERVATIONS: No

BODY WEIGHT: Yes
- Time schedule for examinations (treatment period): Day 0 (the day before the start of treatment) and on Days 7, 14, 21 and 28
- Time schedule for examinations (treatment-free period): Days 35 and 42

Body weights were also recorded at necropsy.

FOOD CONSUMPTION AND COMPOUND INTAKE:
- Food consumption for each group determined and mean weekly diet consumption calculated as g food/kg body weight/week: Yes
- Compound intake calculated as time-weighted averages from the consumption and body weight gain data: No

FOOD EFFICIENCY:
- Change in mean bodyweight (g)/ mean food consumption (g/rat/week): Yes

WATER CONSUMPTION AND COMPOUND INTAKE: Yes
- Time schedule for examinations: daily from Day 8 onwards

OPHTHALMOSCOPIC EXAMINATION: No

HAEMATOLOGY: Yes
- Time schedule for collection of blood: animals from the treatment groups at the end of the treatment period (Day 28) and satellite group animals at the end of the treatment-free period (Day 42).
- Anaesthetic used for blood collection: No
- Animals fasted: No
- How many animals: all animals from the treatment groups and recovery groups
- Parameters checked: haematocrit, haemoglobin, erythrocyte count, total leucocyte count, differential leucocyte count, platelet count, mean corpuscular haemoglobin, mean corpuscular volume, mean corpuscular haemoglobin concentration, and clotting time

CLINICAL CHEMISTRY: Yes
- Time schedule for collection of blood: animals from the treatment groups at the end of the treatment period (Day 28) and satellite group animals at the end of the treatment-free period (Day 42).
- Animals fasted: No
- How many animals: all animals from the treatment groups and recovery groups
- Parameters checked: blood urea, total protein, albumin, albumin/globulin ratio (by calculation), sodium, potassium, chloride, calcium, inorganic phosphorus, alkaline phosphatase, alanine aminotransferase, aspartate aminotransferase, glucose, total bilirubin, and creatinine

URINALYSIS: No
NEUROBEHAVIOURAL EXAMINATION: No
IMMUNOLOGY: No

Sacrifice and pathology:

GROSS PATHOLOGY: Yes
HISTOPATHOLOGY: Yes

On completion of the dosing period or, in the case of satellite group animals, at the end of the treatment-free period; all animals were killed.

Gross pathology:
All animals were subjected to a full external and internal examination, and any macroscopic abnormalities were recorded.

Organ weights:
The following organs from animals that were killed at the end of the study, dissected free from fat, were weighed before fixation: adrenals, brain, gonads, heart, kidneys, liver, pituitary, and spleen.

Histopathology:
Samples of the following tissues were removed from all animals and preserved: adrenals, aorta (thoracic), bone & bone marrow (femur), bone & bone marrow (sternum), brain, caecum, colon, duodenum, eyes, gross lesions, heart, ileum, jejunum, kidneys, liver, lungs, lymph nodes (cervical and mesenteric), muscle (skeletal), oesophagus, ovaries, pancreas, pituitary, prostate, rectum, salivary glands, sciatic nerve, seminal vesicles, skin (hind limb), spleen, stomach, testes, thymus, thyroid/parathyroid, trachea, urinary bladder, and uterus.
The following preserved tissues from all animals (treatment groups, recovery groups, and control groups) were prepared as paraffin blocks, sectioned (5 µm) and stained for microscopic examination:
adrenals, spleen, heart, kidneys, liver, and testes. Macroscopically observed lesions were also processed.
Initially, microscopic examination was performed on control and 1000 mg/kg bw/day dose groups of the treatment period only but since there were indications of treatment-related renal changes, examination was subsequently extended to include sections of kidneys from all animals in the remaining dose groups.

Statistics:

Data were processed to give group mean values and standard deviations where appropriate.
Absolute and relative organ weights, haematological and blood chemical data were analysed by one way analysis of variance incorporating 'F-max' test for homogeneity of variance. Data showing heterogeneous variances were analysed using Kruskal Wallis non-parametric analysis of variance and Mann Whitney U-Test.

Clinical signs:

no effects observed

Mortality:

no mortality observed

Body weight and weight changes:

no effects observed

Food consumption and compound intake (if feeding study):

no effects observed

Food efficiency:

no effects observed

Water consumption and compound intake (if drinking water study):

effects observed, treatment-related

Description (incidence and severity):

1000 mg/kg bw/day: animals of either sex showed a slightly greater water intake than controls during the study, which regressed in satellite high dose animals immediately upon cessation of treatment.

Ophthalmological findings:

not examined

Haematological findings:

no effects observed

Clinical biochemistry findings:

effects observed, treatment-related

Description (incidence and severity):

1000 mg/kg bw/day: males showed a slight but statistically significant increase in plasma potassium and calcium levels compared with controls together with a slight reduction in plasma chloride concentration. Differences between the plasma electrolyte levels of test and control animals were no longer evident amongst satellite group animals following a further fourteen days without treatment.

Urinalysis findings:

not examined

Behaviour (functional findings):

not examined

Immunological findings:

not examined

Organ weight findings including organ / body weight ratios:

effects observed, treatment-related

Description (incidence and severity):

Liver:
1000 mg/kg bw/day: animals of either sex showed a statistically significant increase in liver weight, both absolute and relative to body weight, compared with controls with several of the individual values outside the normally expected ranges for rats of the strain and age used in the study. Increased liver weights were no longer evident in satellite animals following a further fourteen days without treatment.

Gross pathological findings:

no effects observed

Neuropathological findings:

no effects observed

Histopathological findings: non-neoplastic:

no effects observed

Histopathological findings: neoplastic:

not examined

Other effects:

not examined

Details on results:

CLINICAL SIGNS:
15 mg/kg bw/day: animals showed no clinically observable abnormalities during the study.

150 mg/kgbw/day: two animals (1 female / 1 male) showed short-lived increased salivation immediately after' dosing on Days 13 and 14 respectively.
One female showed evidence of minor physical damage around the mouth during the final week of dosing but this isolated finding showed no dose-relationship and, as such, was considered not to be indicative of test material toxicity.

1000 mg/kg bw/day: animals of either sex showed short-lived increased salivation either before or immediately after dosing from Day 3 onwards together with associated findings of fur wetting, red/brown staining around the mouth and, on two isolated occasions, noisy respiration and red/brown staining of the fur. More persistent increased salivation was also seen intermittently at this dose level from Day 5. Satellite high dose animals showed no clinical signs following cessation of treatment.

One satellite high dose female had a distended abdomen, confined to the left side of the body, from Day 8 onwards. The condition persisted throughout the fourteen day recovery period with the animal showing a further slight deterioration in health from Day 37, also appearing emaciated. No gastrointestinal tract abnormality was recorded at necropsy and the change in appearance was considered not to be associated with test material toxicity.

MORTALITY:
15, 150, and 1000 mg/kg bw/day: no deaths

BODY WEIGHT:
15, 150, and 1000 mg/kg bw/day: all animals showed normal body weight development during the study.
Animals treated with test material showed similar body weight gains to controls over the treatment period.

FOOD CONSUMPTION:
15, 150, and 1000 mg/kg bw/day: no adverse effect on food consumption during the study.

FOOD EFFICIENCY:
15, 150, and 1000 mg/kg bw/day: animals treated with the test material showed similar weekly food efficiences to controls.

WATER CONSUMPTION:
15 and 150 mg/kg bw/day: water intake was unaffected by treatment

HAEMATOLOGY:
15, 150, and 1000 mg/kg bw/day: no treatment-related changes in the haematological parameters measured

1000 mg/kg bw/day: males showed a slight but statistically significant increase in mean corpuscular volume compared with controls but all individual values were within the normally expected range for rats of the strain and age used in the study and this intergroup difference was considered to be fortuitous. Satellite females had a higher neutrophil count than controls at the end of the fourteen day recovery period but in the absence of a similar finding at the end of the twenty-eight day dosing period, this difference between test and control animals was considered not to be toxicologically significant.

15 and 150 mg/kg bw/day: the remaining statistically significant intergroup differences were confined to an increased platelet count. These findings were not dose-related and were considered not to be treatment-related.

CLINICAL CHEMISTRY:
1000 mg/kg bw/day dose group females and animals from the 15 and 150 mg/kg bw/day dose groups showed no treatment-related changes in the blood chemical parameters measured.

1000 mg/kg bw/day: females showed a slight but statistically significant increase in plasma glucose concentration compared with controls but none of the individual values were unusually high for rats of the strain and age used in the study and this finding was considered not to be toxicologically significant. Satellite females showed a lower plasma urea concentration than controls after a further fourteen days without treatment together with a higher plasma bilirubin level. Again, none of the individual values were outside the normally expected range for rats of the strain and age used and as neither parameter was
affected by treatment at the end of the twenty-eight day dosing period, the intergroup differences were considered to have arisen fortuitously.

The remaining statistically significant intergroup differences were confined to an increase in plasma calcium and creatinine levels in 150 mg/kg bw/day dose group females. These findings were not dose-related and, as such, were considered not to be toxicologically significant.

ORGAN WEIGHTS:
15 and 150 mg/kg bw/day: no treatment-related organ weight changes

1000 mg/kg bw/day: males showed a slight increase in absolute and relative kidney weight compared with controls and although the intergroup difference in relative kidney weight failed to achieve statistical significance and none of the individual values were abnormally high for rats of the strain and age used, relative kidney weight remained slight elevated (statistically significant) amongst satellite males at the end of the fourteen day recovery period. These findings may be associated with the morphological renal changes detected at this dose level.

1000 mg/kg bw/day: males and females showed a slight but statistically significant reduction in relative heart and spieen weight respectively. None of the individual values were outside the normally expected ranges for rats of the strain and age used in the study and, in the absence of any histopathological evidence of either myocardial or splenic changes, these intergroup differences were considered not to be toxicologically significant.

The remaining statistically significant intergroup differences were confined to a reduced relative brain weight for 15 and 1000 mg/kg bw/day dose group females and a reduction in relative heart and kidney weight for 150 mg/kg/day dose group females. These findings showed no dose relationship and were considered not to be toxicologically important.

GROSS PATHOLOGY:
15, 150, and 1000 mg/kg bw/day: macropscopic kidney changes were observed at terminal kill.

1000 mg/kg bw/day: with the exception of one female, all animals had speckled kidneys at necropsy which were often also pale compared with those of control animals. Furthermore, slightly speckled kidneys were still evident for several satellite animals following a further fourteen days without treatment.

150 mg/kg bw/day: speckled kidneys were observed for all males and one female from this dose group

15 mg/kg bw/day: speckled kidneys were apparent for three animals (1 male / 2 females).

1000 mg/kg bw/day: the liver of four satellite females was also speckled at the end of the fourteen day recovery period but the toxicological significance of this finding is dubious as a similar macroscopic liver change was not detected at the end of the twenty-eight day dosing period.

Hydronephrosis was identified in two animals at terminal kill but this represents a normally-expected, low incidence finding in laboratory maintained rats of the strain and age used and, as such, was considered not to be toxicologically significant.

HISTOPATHOLOGY:
150 and 1000 mg/kg bw/day: treatment-related renal changes were observed. Globules of eosinophilic material were observed in the proximal tubular epithelium of male rats. Female rats were unaffected. Accumulations of eosinophilic material were also observed amongst satellite 1000 mg/kg bw/day male rats although the reduced severity and incidence indicated some regression of the condition following an additional fourteen days without treatment.

All remaining morphological changes were those commonly observed in laboratory maintained rats of the age and strain employed and, since there were no differences in incidence or severity between control and treatment groups, all were considered to be without toxicological significance.

Key result

Dose descriptor:

NOAEL

Effect level:

150 mg/kg bw/day (actual dose received)

Based on:

test mat.

Sex:

male/female

Basis for effect level:

organ weights and organ / body weight ratios

Critical effects observed:

not specified

Conclusions:

After the oral administration of 15, 150, or 1000 mg/kg bw/day of the test item no deaths occurred during the study. Furthermore, no treatment-releated effects were observed for clinical signs, body weight and weight changes, food consumption, food efficiency, and haematology.

During necrospy, speckled kidneys were apparent for one male and two female rats of the 15 mg/kg bw/day dose level and in all males and one female of the 150 mg/kg bw/day dose level group. Globules of eosinophilic material were observed in the proximal tubular epithelium of male rats of the 150 mg/kg bw/day dose group.

At the 1000 mg/kg bw/day dose level, animals of either sex showed a statistically significant increase in relative and absolute liver weight. Increased liver weights were no longer evident in satellite animals following a further fourteen days without treatment. Male animals showed a slight increase in absolute and relative kidney weight compared with controls and although the intergroup difference in relative kidney weight failed to achieve statistical significance and none of the individual values were abnormally high for rats of the strain and age used, relative kidney weight remained slightly elevated (statistically significant) amongst satellite males at the end of the fourteen day recovery period. These findings may be associated with the morphological renal changes detected at this dose level. In addition, at the 1000 mg/kg bw/day dose level, macroscopic kidney changes were observed at terminal kill. With the exception of one female, all animals had speckled kidneys at necropsy which were often also pale compared with those of control animals. Furthermore, slightly speckled kidneys were still evident for several satellite animals following a further fourteen days without treatment. Also, at this high dose level, treatment-related renal changes were observed. Globules of eosinophilic material were observed in the proximal tubular epithelium of male rats. Females were unaffected. Accumulations of eosinophilic material were also observed amongst satellite 1000 mg/kg bw/day male rats although the reduced severity and incidence indicated some regression of the condition following an additional fourteen days without treatment. Lastly, the results of 1000 mg/kg/day dose level showed that animals of either sex had a slightly greater water intake than controls during the study, which regressed in satellite high dose animals immediately upon cessation of treatment and that males showed a slight but statistically significant increase in plasma potassium and calcium levels compared with controls together with a slight reduction in plasma chloride concentration. Differences between the plasma electrolyte levels of test and control animals were no longer evident amongst satellite group animals following a further fourteen days without treatment.
Based on the organ weights of liver, a No Observed Adverse Effect Level (NOAEL) for test item of 150 mg/kg bw/day was concluded for males and females.

Executive summary:

A repeated dose oral toxicity study was performed with the test item according to the OECD guideline 407 (1981). The test material was administered by gavage to three groups, each of five male and five female Sprague-Dawley CD strain rats, for twenty-eight consecutive days, at dose levels of 15, 150 and 1000 mg/kg bw/day. A control group of five males and five females was dosed with vehicle alone (arachis oil B.P.). Two satellite groups, each of five males and five females, were treated with the high dose (1000 mg/kg bw/day) or the vehicle alone throughout the twenty-eight day study period and then maintained without treatment for a further fourteen days. The following parameters were evaluated: clinical signs, body weight, food consumption, food efficiency, water consumption, haematology, clinical chemistry, organ weights, macroscopic examination, and histopathology of selected tissues.

After the oral administration of 15, 150, or 1000 mg/kg bw/day of the test item no deaths occurred during the study. Furthermore, no treatment-releated effects were observed for clinical signs, body weight and weight changes, food consumption, food efficiency, and haematology.

During necrospy, speckled kidneys were apparent for one male and two female rats of the 15 mg/kg bw/day dose level and in all males and one female of the 150 mg/kg bw/day dose level group. Globules of eosinophilic material were observed in the proximal tubular epithelium of male rats of the 150 mg/kg bw/day dose group.

At the 1000 mg/kg bw/day dose level, animals of either sex showed a statistically significant increase in relative and absolute liver weight. Increased liver weights were no longer evident in satellite animals following a further fourteen days without treatment. Male animals showed a slight increase in absolute and relative kidney weight compared with controls and although the intergroup difference in relative kidney weight failed to achieve statistical significance and none of the individual values were abnormally high for rats of the strain and age used, relative kidney weight remained slightly elevated (statistically significant) amongst satellite males at the end of the fourteen day recovery period. These findings may be associated with the morphological renal changes detected at this dose level. In addition, at the 1000 mg/kg bw/day dose level, macroscopic kidney changes were observed at terminal kill. With the exception of one female, all animals had speckled kidneys at necropsy which were often also pale compared with those of control animals. Furthermore, slightly speckled kidneys were still evident for several satellite animals following a further fourteen days without treatment. Also, at this high dose level, treatment-related renal changes were observed. Globules of eosinophilic material were observed in the proximal tubular epithelium of male rats. Females were unaffected. Accumulations of eosinophilic material were also observed amongst satellite 1000 mg/kg bw/day male rats although the reduced severity and incidence indicated some regression of the condition following an additional fourteen days without treatment. Lastly, the results of 1000 mg/kg/day dose level showed that animals of either sex had a slightly greater water intake than controls during the study, which regressed in satellite high dose animals immediately upon cessation of treatment and that males showed a slight but statistically significant increase in plasma potassium and calcium levels compared with controls together with a slight reduction in plasma chloride concentration. Differences between the plasma electrolyte levels of test and control animals were no longer evident amongst satellite group animals following a further fourteen days without treatment.

Based on the organ weights of liver, a No Observed Adverse Effect Level (NOAEL) for test item of 150 mg/kg bw/day was concluded for males and females.

Endpoint conclusion

Endpoint conclusion:

adverse effect observed

Dose descriptor:

NOAEL

150 mg/kg bw/day

Study duration:

subacute

Species:

rat

System:

hepatobiliary

Organ:

liver

Repeated dose toxicity: inhalation - systemic effects

Link to relevant study records

Reference

Endpoint:

short-term repeated dose toxicity: inhalation

Data waiving:

study scientifically not necessary / other information available

Justification for data waiving:

other:

Endpoint conclusion

Endpoint conclusion:

no study available

Repeated dose toxicity: inhalation - local effects

Link to relevant study records

Reference

Endpoint:

short-term repeated dose toxicity: inhalation

Data waiving:

study scientifically not necessary / other information available

Justification for data waiving:

other:

Endpoint conclusion

Endpoint conclusion:

no study available

Repeated dose toxicity: dermal - systemic effects

Link to relevant study records

Reference

Endpoint:

short-term repeated dose toxicity: dermal

Data waiving:

study scientifically not necessary / other information available

Justification for data waiving:

other:

Endpoint conclusion

Endpoint conclusion:

no study available

Repeated dose toxicity: dermal - local effects

Link to relevant study records

Reference

Endpoint:

short-term repeated dose toxicity: dermal

Data waiving:

study scientifically not necessary / other information available

Justification for data waiving:

other:

Endpoint conclusion

Endpoint conclusion:

no study available

Justification for classification or non-classification

A repeated dose oral toxicity study according to OECD Guideline 407 in which the test material was administered by gavage Sprague-Dawley rats, for twenty-eight consecutive days, at dose levels of 15, 150 and 1000 mg/kg/day is considered as the key study for repeated dose toxicity and will be used for classification. Based on a slight increase in liver weights which was reversible after 14 days recovery period, the no observed adverse effect level (NOAEL) was established at 150 mg/kg bw/day.

 

The classification criteria according to Regulation (EC) No 1272/2008 as specific target organ toxicant (STOT) – repeated exposure, oral are not met since no irreversible adverse health effects and only minor and reversible relative liver weight increase was observed immediately after exposure, which abate after the recovery period. The no observed adverse effect level (NOAEL) via oral application is above the guidance value for a Category 1 classification of 30 mg/kg bw/day and only slightly below the guidance value for a Category 2 classification of 300 mg/kg bw/day. Considering the large dose spacing from 150 to 1000 mg/kg bw/day and the reversible adaptive changes in the liver only seen at the highest dose, the criteria for the classification for specific target organ toxicant (STOT) – repeated exposure, oral are not met.