Reaction mass of (R)-2-(3-(diisopropylamino)-1-phenylpropyl)-4-(hydroxymethyl)phenol and Methylene Chloride

Repeated dose toxicity: oral

Administrative data

Endpoint:

short-term repeated dose toxicity: oral

Remarks:

28 Days

Type of information:

experimental study

Adequacy of study:

key study

Study period:

25 March - 14 April 1999

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Data source

Reference

Reference Type:

study report

Title:

Unnamed

Year:

2004

Report date:

2004

Materials and methods

Test guideline

Qualifier:

according to guideline

Guideline:

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

GLP compliance:

yes (incl. QA statement)

Limit test:

yes

Test material

Test material information

Constituent 1

Reference substance name:

4-chloro-6-ethyl-5-fluoropyrimidine; dichloromethane

EC Number:

929-144-0

IUPAC Name:

4-chloro-6-ethyl-5-fluoropyrimidine; dichloromethane

Test material form:

liquid

Details on test material:

Clear yellow liquid
Storage conditions: Room temperature in the dark

Specific details on test material used for the study:

Clear yellow liquid
Stored at room temperature and protected from light
Batch No: 6603/0651

Test animals

Species:

rat

Strain:

other: Crl: CDe (SD) IGS BR

Details on species / strain selection:

The rat was chosen because of its acceptance as a predictor of toxic change in man and the requirement for a rodent species by regulatory agencies. The CD® (SD) IGS BR strain was used because of the historical control data available in this laboratory.

Sex:

male/female

Details on test animals or test system and environmental conditions:

A total of 25 male and 25 female rats of the Crl: CDe (SD) IGS BR strain, 26 to 30 days of age, were obtained from Charles River (UK) Limited, Margate, Kent, England. For Groups 1 to 4, the male animals used on the study weighed 139-177 g on the day that treatment commenced; the females were within the bodyweight range 128-156 g at this time.
The subsequent additional group of animals (Group 5: treated at 11 mg/kg/day) employed the surplus animals from this study; these animals were delivered from the same source at the same time as the animals for this study. On the day that dosing commenced for these animals, the male animals were within the bodyweight range 199-250 g and the females were 163-183 g.
After random allocation to groups each animal was assigned a number and identified uniquely within the study by a tail tattoo that was checked at regular intervals and renewed if necessary.
The animals were allowed to acclimatise to the conditions described below for at least twelve days before commencement of treatment. The animals from Groups 1 to 4 were approximately 38 to 42 days of age when treatment started; the animals of Group 5 were 46 to 50 days of age when treatment
commenced.
Animals were housed inside a barriered rodent facility.
Each animal room was kept at positive pressure with respect to the outside by its own supply of filtered fresh air which was passed to atmosphere and not re-circulated. Target values within the study room were 21°C for temperature (acceptable range 19-25°C) for temperature, 55% for relative
humidity (acceptable range 40-70%) and at least 10 air changes per hour. Lighting was controlled to provide a 12-hour light : 12-hour dark cycle.
The animals were housed five of one sex per cage in RS Biotech caging which were made of a stainless steel body with a stainless steel mesh lid and
floor.
The animals were allowed free access, except overnight before routine blood sampling, to an expanded rodent dietThis diet contained no added antibiotic or chemotherapeutic or prophylactic agent.
Water taken from the public supply was freely available, via polycarbonate bottles fitted with sipper tubes.
On arrival animals were non-selectively assigned to cages and treatment groups. Using the sequence of cages in the battery, one animal at a time was placed in each cage with the procedure repeated until each cage held the appropriate number of animals. Shortly after arrival, the animals were weighed. Two males and three females were replaced with spare animals from the same batch to minimise inter-group bodyweight variations and one male and one female were also replaced due to ophthalmic abnormalities; these animals were subsequently employed for the additional dosage group that was added to the study at the additional dosage.
As far as was practicable the distribution of animals in the room was designed to minimise the effect of any spatially variable component of the environment.
Composition and identity of treatment groups
Animals were assigned to the groups as follows:
Group Treatment Dosage (mg/kg/day) Cage numbers Animal numbers
Nominal Achieved Male Female Male Female
1 Control 0 0 3 5 11-15 21-25
5* UK- 103,444 15 11 9 10 41-45 46-50
2 UK-103,444 50 41 1 6 1-5 26-30
3 UK-103,444 150 135 4 8 16-20 36-40
4 UK-103,444 500 478 2 7 6-10 31-35

* Treatment commenced eight days after the other groups.
Cage labels, identifying the occupants by experiment, animal number, sex and treatment group, were
colour-coded.

Administration / exposure

Route of administration:

oral: gavage

Details on route of administration:

Oral gavage, to simulate the conditions of potential human exposure.

Vehicle:

methylcellulose

Details on oral exposure:

The test substance was prepared for administration as a series of graded suspensions in aqueous 1% w/v methylcellulose. The suspensions were made by slow addition of the vehicle followed by high speed mixing for three minutes. Initially the formulations were prepared by serial dilution from the
highest dosage, however, in the light of poor achieved concentrations from the Week 1 formulations, independant formulations were prepared for each dosage for the remainder of the study. All formulations were prepared daily on the day before use.

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

The analytical procedure was validated by determining the specificity of the chromatographic analysis, linearity of detector response, precision of injection, limit of detection, method accuracy and precision.

Duration of treatment / exposure:

All animals were treated for 28 consecutive days.

Frequency of treatment:

Once daily, seven days per week.

Doses / concentrations

Doses / concentrations 1

Dose / conc.:

0 mg/kg bw/day (nominal)

Doses / concentrations 2

Dose / conc.:

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

Remarks:

Control: 5 males and 5 females

Doses / concentrations 3

Dose / conc.:

15 mg/kg bw/day (nominal)

Doses / concentrations 4

Dose / conc.:

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

Remarks:

5 males and 5 females

Doses / concentrations 5

Dose / conc.:

50 mg/kg bw/day (nominal)

Doses / concentrations 6

Dose / conc.:

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

Remarks:

5 males and 5 females

Doses / concentrations 7

Dose / conc.:

150 mg/kg bw/day (nominal)

Doses / concentrations 8

Dose / conc.:

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

Remarks:

5 males and 5 females

Doses / concentrations 9

Dose / conc.:

500 mg/kg bw/day (nominal)

Doses / concentrations 10

Dose / conc.:

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

Remarks:

5 males and 5 females

No. of animals per sex per dose:

5 animals per sex per dose (10 total per dose)

Control animals:

yes, concurrent vehicle

Details on study design:

The test substance was prepared for administration as a series of graded suspensions in aqueous 1% w/v methylcellulose. The suspensions were made by slow addition of the vehicle followed by high speed mixing for three minutes. Initially the formulations were prepared by serial dilution from the
highest dosage, however, in the light of poor achieved concentrations from the Week 1 formulations, independant formulations were prepared for each dosage for the remainder of the study.
All formulations were prepared daily on the day before use.
Before treatment commenced the suitability of the proposed mixing procedure, and the homogeneity and stability of the test substance in the vehicle, were determined by a trial preparation. Samples of the formulation were assayed as detailed below:
The distribution of the test substance in the vehicle was assessed at concentrations of 0.5 and 50 mg/m1 by analysing duplicate samples taken from three positions in the mix.
The stability and distribution of the test substance in the vehicle was assessed at concentrations of 0.5 and 50 mg/ml. Samples were taken from a bulk preparation and were stored at 21°C and analysed immediately after preparation and after 1, 2 and 48 hours; additional samples were taken
and stored at 4°C and analysed after 2, 8 and 15 days.
In addition, samples of each formulation prepared for administration during each week of treatment were analysed for achieved concentration of the test substance. The method of analysis was an adaptation of the method supplied by the Sponsor.
The homogeneity and stability of UK-103,444 in the aqueous 1% methylcellulose formulation were confirmed, at nominal concentrations of 0.5 and 50 mg/ml, during ambient temperature storage for 2 days and refrigerated storage for 15 days. The storage period represented the
maximum time from preparation to completion of use.
Investigations into the potential causes for the concentration losses observed indicated that the test substance content was consistent between the samples taken; that sample weights of 1.5 mg, 5 mg and 15 mg could be stored in the control vehicle (1 ml) for 4 hours at ambient temperature without
incurring any concentration loss; but that sample weights of 62 mg and 750 mg incurred a threshold loss in concentration (25 — 30 mg) during ambient temperature fume cupboard storage in an open glass beaker.
Due to the lower than anticipated concentrations, the dosages quoted in this report are achieved rather than nominal values.
Animals received the test substance or vehicle control formulations by gavage at a constant volume-dosage of 10 ml/kg bodyweight. All animals were dosed in sequence of cage-number within each group, once each day, seven days per week. The volume administered to each animal was
calculated from the most recently recorded bodyweight.
All animals were treated for 28 consecutive days.

Examinations

Observations and examinations performed and frequency:

SERIAL OBSERVATIONS:
All observations described below were performed in cage number sequence, except where otherwise indicated.
Signs:
Animals were inspected at least twice daily for evidence of reaction to treatment or ill-health. Any deviations from normal were recorded at the time in respect of nature and severity, date and time of onset, duration and progress of the observed condition, as appropriate.
Daily during the first week of treatment and twice weekly during Weeks 2 to 4 (middle and end of each week) detailed observations were recorded before and after dosing; these observations were recorded at the following times in relation to dosing:
Immediately before dosing.
Immediately after dosing on return of the animal to its cage.
On completion of dosing of each group.
Between one and two hours after completion of dosing of all groups.
As late as possible in the working day.
In addition, a more detailed physical weekly examination was performed on each animal.
Cages and cage-trays were inspected daily for evidence of animal ill-health, such as blood or loose faeces.
During the acclimatisation period, observations of the animals and their cages were recorded at least once per day.
Bodyweight:
Each animal was weighed during the acclimatisation period, on the day that treatment commenced, twice weekly throughout the treatment period and before necropsy.
Food consumption:
The weight of food supplied to each animal, that remaining and an estimate of any spilled was recorded for each week throughout the treatment period. From these records the mean weekly consumption per animal was calculated for each cage.
Food conversion efficiency:
Weekly group mean food conversion efficiencies were calculated.
Water consumption:
Water consumption was assessed throughout the first four weeks of the study, by daily visual inspection and comparison with Controls. Due to the temperal difference, no assessment was undertaken during the last week of treatment for animals treated at 11 mg/kg/day.
FUNCTIONAL OBSERVATIONAL BATTERY:
Each animal was subjected to the procedures detailed below on the specified occasions. The functional observational battery was performed at the same time of day on each occasion and the observer was unaware of the experimental group to which the animal belonged. The animals were
not necessarily all tested on the same day but the number of animals were balanced across the groups on each day of testing. Any deviation from normal was recorded with respect to nature and, where appropriate, degree of severity.
In the hand and standard arena observations:
Observations were performed in the hand and then during a one minute period in a standard arena.
Each animal was examined before treatment commenced and weekly throughout the treatment period.
After removal from the home cage the following parameters were assessed:
In the hand Standard arena:
Exophthalmos Activity counts
Fur appearance Arousal
Lacrimation Convulsion
Piloerection Defaecation count
Reactivity to handling Gait
Ease of removal from cage Grooming
Salivation Palpebral closure
Vocalisation on handling Posture
Rearing count
Tremor
Twitches
Urination
Manipulations:
Before commencement and during Week 4 of treatment the following measurements, reflexes and responses were recorded:
Approach response
Auditory startle reflex
Body temperature
Bodyweight
Grip stregnth - forelimbs and hind limbs
Landing footsplay
Tail pinch response
Pupil closure reflex
Righting reflex
Touch response

Motor activity:
Motor activity was measured before commencement and during Week 4 by automated infra-red sensor equipment, recording individual animal activity over a one hour period.
Haematology, peripheral blood:
On Day 30, blood samples were obtained from all animals after overnight fasting.
Blood samples were withdrawn from the retro-orbital sinus, with the animals held under Isoflurane anaesthesia, and collected into EDTA as anticoagulant. The samples were obtained and analysed in the sequence Group 1, 3 and 2 for males and females. Samples were similarly obtained and analysed on Day 30 from Group 5 animals. All samples were examined for the following characteristics:
Using a Technicon H. 1 haematology analyser -
Packed cell volume (Hct)
Haemoglobin concentration (Hb)
Erythrocyte count (RBC)
Total and differentiae leucocyte count (WBC)
Platelet count (Pit)
Mean cell haemoglobin concentration (MCHC)
Mean cell haemoglobin (MCH)
Mean cell volume (MCV)
The equipment distinguishes neutrophils, lymphocytes, eosinophils, basophils, monocytes and a small proportion of large unstained cells (LUC). Large unstained cells are those cells that the H. 1 analyser is unable to classify as belonging to any of the other classes.
Blood film - Romanowslcy stain, examined by light microscopy for abnormal morphology and unusual cell types, including normoblasts.
Additional blood samples were taken into citrate anticoagulant.
Blood chemistry:
At the same time as for peripheral haematology, further blood samples were taken and collected into lithium heparin as anticoagulant. Samples were taken and analysed in the same sequence as for peripheral haematology.
TERMINAL OBSERVATIONS:
Euthanasia:
Animals surviving to the end of the treatment period and any killed prematurely were killed by carbon dioxide inhalation. The sequence in which the animals were killed after completion of treatment was selected to allow satisfactory inter-group comparison.
Macroscopic pathology:
All animals were subjected to a detailed necropsy.
The necropsy procedure included a review of the history of each animal and a detailed examination of the external features and orifices, the neck and associated tissues and the cranial, thoracic, abdominal and pelvic cavities and their viscera. The requisite organs were weighed and the external and cut surfaces of the organs and tissues were examined as appropriate. Abnormalities and interactions were noted and the required tissue samples preserved in fixative. Before disposal of the carcass the retained tissues were checked against the protocol and a senior
prosector reviewed the necropsy report.
Organ weights:
The following organs, taken from each animal in Groups 1, 2, 3 and 5, were dissected free of adjacent fat and other contiguous tissue and the weights recorded. The weight of each organ was expressed as a percentage of the bodyweight recorded immediately before necropsy. Organ weights were not taken for animals dying during the study.
Adrenals Ovaries
Brain Spleen
Epididymides Testes
Heart Thymus
Kidneys Uterus with cervix.
Liver
Tissues preserved for histopathology:
Samples of the following tissues were preserved in 10% neutral buffered formalin, with the exception of testes and epididymides that were initially placed in Bouin's fluid and subsequently retained in 70% industrial methylated spirit.
Adrenals Ovaries
Brain Pancreas
Bronchi Prostate
Caecum Rectum
Colon Sciatic nerve
Duodenum Seminal vesicles
Epididymides Spinal cord
Femur with joint Spleen
Heart Sternum
Ileum Stomach
Jejunum Testes
Kidneys Thymus
Liver Thyroid with parathyroids
Lungs Trachea
Lymph nodes - mandibular Urinary bladder
- mesenteric Uterus and cervix
Oesophagus Vagina.
Samples of any abnormal tissues were also retained for histopathological examination. In those cases where a lesion was not clearly delineated, contiguous tissue was fixed with the grossly affected region and sectioned as appropriate.
Tissues preserved, but not examined:
Samples of the head (including nasal cavity, paranasal sinuses and nasopharynx) and the remaining sciatic nerve were preserved in 10% neutral buffered formalin. These tissues were not examined histologically, but are retained against any future requirement for microscopic examination.
Histology:
Tissue samples preserved for histopathology from all animals were dehydrated, embedded in paraffin wax, sectioned at approximately four to five micron thickness and stained with haematoxylin and eosin with the exception of testes which were stained using a standard Periodic Acid/Schiff method.
The tissues subjected to histological processing included the following regions:
Adrenals - cortex and medulla
Brain — cerebellum, cerebrum and midbrain
Femur with joint — longitudinal section including bone marrow
Heart - including auricular and ventricular regions
Ileum — including Peyers patch, where possible
Kidneys - including cortex, medulla and papilla region
Liver - section from each of the five major lobes
Lungs — section from two major lobes, to include bronchi
Spinal cord — transverse and longitudinal section at the cervical level
Stomach - including keratinised, ftindic and pyloric mucosa in sections.
Thyroid — including parathyroids in section where possible
Uterus — uterus section separate from cervix section.
For bilateral organs, sections of both the left and right organs were examined. A single section was prepared from each of the remaining tissues required for microscopic pathology.
Microscopy:
Microscopic examination was performed on the tissue sections listed above, taken from all animals of Groups 1, 3 and 4. Tissues reported at macroscopic examination as being abnormal were examined for all animals of Groups 2 and 5.
Findings were either reported as "Present" or assigned a severity grade. In the latter case one of the following five grades was used - minimal, slight, moderate, marked or severe.

Sacrifice and pathology:

Animals surviving to the end of the treatment period and any killed prematurely were killed by carbon dioxide inhalation. The sequence in which the animals were killed after completion of treatment was selected to allow satisfactory inter-group comparison.

Results and discussion

Results of examinations

Clinical signs:

not examined

Mortality:

mortality observed, treatment-related

Description (incidence):

The mortality distribution was as follows:
Dosage Male Female Combined
(mg/kg/day)
11 0/5 0/5 0/10
41 0/5 0/5 0/10
135 0/5 0/5 0/10
478 5(4)/5 5(1)/15 10(5)/10

Figures in parentheses indicate the number of animals found dead.

Animals treated at 478 mg/kg/day either died during the first overnight period or were humanely
killed on the following morning due to the marked signs of toxicity. Ante mortem signs included
underactivity, cold to touch, piloerection, ungroomed condition, salivation, muscle tremors, eyes
partially closed, hunched posture, prone posture, respiratory irregularities and fur staining.

No clinical sign attributable to treatment with UK-103,444 was evident amongst animals treated at dosages up to 135 mg/kg/day and no animal died.

Body weight and weight changes:

no effects observed

Description (incidence and severity):

It was considered that there was no effect of treatment on bodyweight gain.

Food consumption and compound intake (if feeding study):

no effects observed

Description (incidence and severity):

Food consumption was unaffected by treatment.

Food efficiency:

no effects observed

Description (incidence and severity):

Food conversion efficiency was considered to have been unaffected by treatment at dosages up to 135 mg/kg/day.

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

no effects observed

Description (incidence and severity):

It was considered that there was no effect of treatment on the visual assessment of water consumption.

Ophthalmological findings:

not examined

Haematological findings:

effects observed, non-treatment-related

Description (incidence and severity):

Haematological examination after four weeks of treatment, when compared with the Controls and historic background data, showed no disturbance considered to reflect an effect of treatment. A number of inter-group differences attained statistical significance but they were minor or lacked dosage-relationship and were, therefore, not attributed to treatment with UK-103,444.

Clinical biochemistry findings:

effects observed, treatment-related

Description (incidence and severity):

After four weeks of treatment plasma alanine amino-transferase activities of females treated at 41 mg/kg/day or above was less than the Controls; a dosage-relationship was apparent.
The plasma urea concentrations in females receiving 135 mg/kg/day were slightly low in comparison with the Controls; males were unaffected.
There was no other disturbance in the blood plasma, when compared with the Controls or historic background data, that was attributable to treatment with UK-103,444.
A number of inter-group differences attained statistical significance but they were minor or lacked dosage-relationship and were considered to reflect natural variation.

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):

The bodyweight relative and absolute liver weights of animals treated at 135 mg/kg/day were slightly higher than the Controls after four weeks of treatment.

Gross pathological findings:

no effects observed

Description (incidence and severity):

No treatment related macroscopic abnormality was evident

Neuropathological findings:

not examined

Histopathological findings: non-neoplastic:

not examined

Histopathological findings: neoplastic:

not examined

Other effects:

effects observed, non-treatment-related

Description (incidence and severity):

In the hand observations: There was no treatment-related finding.

Arena observations: Observations in the standard arena showed some inter-group variation, with group mean rearing and activity scores for males and females in treated groups tending to be somewhat lower than those of Controls during Weeks 2 to 4 of treatment. These differences were not, however, statistically significant and there was no clear or consistent dosage-relationship. Behaviour in the arena was therefore considered to be unaffected by treatment.
Manipulations: There was no finding considered to be associated with treatment. Compared with Controls, animals receiving 11 mg/kg/day showed increased grip strength, bodyweight and body temperature values, before commencement of treatment, during Week 4 of treatment, or both. These differences were considered to be due to these animals starting treatment approximately one week later, and therefore one week older than other study animals.
Motor activity:
Motor activity scores were considered to have been unaffected by treatment.
Although group mean motor activity scores showed considerable inter and intra-group variation there was no statistically significant difference in the total scores and no consistent treatment or dosagerelated trends during Week 4 of treatment. Rearing scores for females receiving 135 mg/kg/day were slightly higher than those of Controls during Week 4 of treatment but these differences were also apparent, to a lesser extent, before commencement of treatment and were considered to be due to natural variation.
Microscopic pathology:
Histopathological examination of the decedents (treated at 478 mg/kg/day) revealed periacinar coagulative necrosis in the livers of three males and all females and focal necrosis of the glandular mucosa of the stomach in two males and two females.
Thickened growth plate and articular cartilage of the femur was apparent in all decedents (treated at 478 mg,/kg/day) and there was an absence of maturation phase spermatids, accompanied by hypospernna, in the epididymides and reduced seminal vesicle secretions in all males of this group.
These findings are considered to reflect the immaturity of the animals rather than an effect of the test material.
Histopatholgical examination of animals treated at 135 mg/kg/day or less, revealed no abnormality considered to reflect an effect of the test material.

Details on results:

Animals treated at 478 mg/kg died, or were humanely killed, after the first administration due to severe toxic effects seen. Histopathological examination revealed periacinar coagulative necrosis in the livers of three males and all females and focal necrosis of the glandular mucosa of the stomach of two males and two females.
Amongst animals treated at 135 mg/kg/day or less, there was no death and no sign of reaction to treatment.
Bodyweight gain, food and water consumption and the efficiency of food utilisation were unaffected by treatment up to 135 mg/kg/day.
Four weeks of treatment with UK-103,444 at dosages up to 135 mg/kg/day did not result in any change in performance in the functional observation battery that was considered to be indicative of neurotoxicity.
There was no treatment-related haematological change.
After four weeks of treatment, plasma alanine amino-transferase activities were low in females receiving 41 or 135 mg/kg/day and plasma urea concentrations were slightly low in females receiving 135 mg/kg/day.
The liver weights of animals treated at 135 mg/kg/day were slightly high in comparison with the Controls.
There was no treatment-related macroscopic or histopathological abnormality at dosages up to 135 mg/kg/day.

Effect levels

1

Key result

Dose descriptor:

NOAEL

Effect level:

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

Based on:

test mat.

Sex:

male/female

Basis for effect level:

clinical biochemistry

haematology

mortality

organ weights and organ / body weight ratios

2

Key result

Dose descriptor:

NOEL

Effect level:

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

Based on:

test mat.

Sex:

male/female

Basis for effect level:

clinical biochemistry

haematology

mortality

organ weights and organ / body weight ratios

Target system / organ toxicity

1

Critical effects observed:

yes

Lowest effective dose / conc.:

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

System:

hepatobiliary

Organ:

liver

Treatment related:

yes

2

Critical effects observed:

yes

Lowest effective dose / conc.:

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

System:

gastrointestinal tract

Organ:

stomach

Treatment related:

yes

Applicant's summary and conclusion

Conclusions:

Administration to CD rats of UK-103,444, a pharmaceutical intermediate, at a dosage of 478 mg/kg (nominal dosage of 500 mg/kg) elicited a clear toxic response after a single administration, resulting in the death of all animals. Histopathological examination of these animals revealed necrosis of the liver and glandular mucosa. It was considered that the hepatic changes were responsible for the death of some individuals; the stomach changes were thought to reflect test material irritancy.
The daily administration of UK-103,444 at dosages of 11, 41 or 135 mg/kg/day (nominal dosages of 15, 50 or 150 mg/kg/day) for four weeks was well-tolerated with no death. An effect upon the liver was indicated by high liver weights in animals given 135 mg/kg/day. The variation in plasma alanine amino-transferase activities and urea concentrations are probably the result of an alteration in hepatic metabolism following the administration of a xenobiotic. There was, however, no associated microscopic correlate and the effect upon the liver was, therefore, considered to be an adaptive response of no toxicological significance.

Executive summary:

The No-Observed-Adverse-Effect Level (NOAEL), in this study was considered to be 135 mg/kg/day and the No-Observed-Effect Level (NOEL) was identified as 11 mg/kg/day.