2-methylbutane

Repeated dose toxicity: oral

Administrative data

Endpoint:

short-term repeated dose toxicity: oral

Type of information:

experimental study

Adequacy of study:

supporting study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: see 'Remark'

Remarks:

This study is classified as reliable with restrictions even though it is not noted whether the study followed GLPs and was not conducted in accordance with guidelines. This is because the study’s goal was to examine nephrotoxicity, not systemic toxicity as outlined in OECD guideline 407. Study methods are well-documented and scientifically sound.

Cross-reference

Reason / purpose for cross-reference:

reference to same study

Data source

Reference

Reference Type:

publication

Title:

Unnamed

Year:

1985

Materials and methods

Test guideline

Qualifier:

no guideline followed

Principles of method if other than guideline:

The study’s goal was to examine nephrotoxicity, not systemic toxicity as outlined in OECD guideline 407. When comparing the study's methods to OECD 407, the following limitations were noted: no female rats were tested; only two dose groups were tested at fairly high doses for a substance that can be aspirated; the only post-necropsy examinations were of the kidney.

GLP compliance:

not specified

Limit test:

no

Test material

Test material information

Constituent 1

Reference substance name:

2-methylbutane

EC Number:

201-142-8

EC Name:

2-methylbutane

Cas Number:

78-78-4

Molecular formula:

C5H12

IUPAC Name:

2-methylbutane

Details on test material:

- Name of test material (as cited in study report): 2-methylbutane
- Substance type: C5 aliphatics
- Analytical purity: not reported

Test animals

Species:

rat

Strain:

Fischer 344

Sex:

male

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Charles River Breeding Laboratories, Kingston, New York
- Age at study initiation: 9 weeks
- Weight at study initiation: 171 to 194 grams
- Fasting period before study: not reported
- Housing: individual, suspended polycarbonate cages
- Diet (e.g. ad libitum): ad libitum
- Water (e.g. ad libitum): ad libitum
- Acclimation period: 2 weeks

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 24 to 26 degrees celsius
- Humidity (%): 40 to 80 %
- Air changes (per hr): not reported
- Photoperiod (hrs dark / hrs light): 12 hours dark and 12 hours light

Administration / exposure

Route of administration:

oral: gavage

Vehicle:

unchanged (no vehicle)

Details on oral exposure:

PREPARATION OF DOSING SOLUTIONS: calculated based on body weights taken prior to dosing on day 1, appropriate dosing volume was determined using specific gravity

Analytical verification of doses or concentrations:

not specified

Duration of treatment / exposure:

4 weeks

Frequency of treatment:

once daily, 5 days per week

Doses / concentrations

Doses / concentrations 1

Remarks:

Doses / Concentrations:
0.5 g/kg/day
Basis:
no data

Doses / concentrations 2

Remarks:

Doses / Concentrations:
2.0 g/kg/day
Basis:
no data

No. of animals per sex per dose:

10

Control animals:

yes

Details on study design:

- Dose selection rationale: pilot study
- Negative control: isotonic saline at a dose of 2.0 g/kg/day

Positive control:

Unleaded gasoline

Examinations

Observations and examinations performed and frequency:

CAGE SIDE OBSERVATIONS: yes
- Time schedule: twice daily

DETAILED CLINICAL OBSERVATIONS: yes
- Time schedule: twice daily

BODY WEIGHT: yes
- Time schedule for examinations: prior to dosing and at scheduled sacrifice

FOOD EFFICIENCY: not reported

WATER CONSUMPTION AND COMPOUND INTAKE (if drinking water study): no

OPHTHALMOSCOPIC EXAMINATION: no

HAEMATOLOGY: no

CLINICAL CHEMISTRY: no

URINALYSIS: no

NEUROBEHAVIOURAL EXAMINATION: no

Sacrifice and pathology:

GROSS PATHOLOGY: yes (stated, no data provided)
HISTOPATHOLOGY: yes (kidney only)

Statistics:

mean and standard deviations calculated for body weight, kidney weight, and kidney pathology data; statistical significance calculated using Studen t-test and Mann-Whitney U test

Results and discussion

Results of examinations

Clinical signs:

effects observed, treatment-related

Mortality:

mortality observed, treatment-related

Body weight and weight changes:

effects observed, treatment-related

Food consumption and compound intake (if feeding study):

not examined

Food efficiency:

not examined

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

not examined

Ophthalmological findings:

not examined

Haematological findings:

not examined

Clinical biochemistry findings:

not examined

Urinalysis findings:

not examined

Behaviour (functional findings):

not examined

Organ weight findings including organ / body weight ratios:

no effects observed

Gross pathological findings:

no effects observed

Histopathological findings: non-neoplastic:

no effects observed

Histopathological findings: neoplastic:

not examined

Details on results:

MORTALITY
10% of low dose rats, 90% of high dose rats

TERMINAL BODY WEIGHT
significantly lower than saline control at the low dose (p < 0.05), not calculated at high dose due to high mortality

KIDNEY WEIGHTS
not significantly different than controls at low dose, not calculated at high dose due to high mortality

GROSS PATHOLOGY
no effects

HISTOPATHOLOGY: KIDNEY
not significantly different than controls at low dose, not calculated at high dose due to high mortality

Effect levels

Dose descriptor:

NOAEL

Remarks on result:

not determinable

Remarks:

no NOAEL identified

Target system / organ toxicity

Critical effects observed:

not specified

Applicant's summary and conclusion

Conclusions:

The results for 2-methylbutane and saline (i.e., the control) were not significantly different. 2-methylbutane was found to cause high mortality at 2.0 g/kg/day.

Executive summary:

The nephrotoxicity of 2-methylbutane was evaluated in male F344 rats over 4 weeks after oral gavage doses of 0.5 g/kg/day and 2.0 g/kg/day. Clinical examinations were conducted twice daily throughout the study, and nephrotoxicity and histopathology of the kidney were evaluated at termination. The results were compared to positive and negative controls. Statistical methods used were appropriate. 

Mortality occurred in 90% of high-dose rats and 10% of low-dose rats. Kidney weights for surviving animals were comparable to controls. 2 -methylbutane's ability to cause hydrocarbon nephropathy was comparable to the saline control (not significantly different).

This study is classified as reliable with restrictions, Klimisch score 2, even though it is not noted whether the study followed GLPs and was not conducted in accordance with guidelines. This is because the study’s goal was to examine nephrotoxicity, not systemic toxicity as outlined in OECD guideline 407. Study methods are well-documented and scientifically sound. However, several study limitations are noted when comparing this study’s methods to OECD 407. First, no female rats were used in the study. Second, the selected dose levels did not cover an appropriate range (i.e., only two dose groups were used, and both were at fairly high doses for a substance that can be aspirated). Third, the substance was administered 5 days/week instead of 7. Fourth, body weight measurements were only taken twice during the experiment (i.e, prior to dosing and at the scheduled sacrifice). Fifth, the only post-necropsy examinations were of the kidney. Finally, functional observations, hematology analysis, urinalysis and other post-necropsy examinations were were conducted.