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Administrative data

short-term repeated dose toxicity: oral
Type of information:
experimental study
Adequacy of study:
key study
Study period:
13th September 2005 - 11th October 2005
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
other: Guideline study performed in accordance with GLP.

Data source

Reference Type:
study report

Materials and methods

Test guidelineopen allclose all
according to guideline
OECD Guideline 407 (Repeated Dose 28-Day Oral Toxicity Study in Rodents)
according to guideline
EU Method B.7 (Repeated Dose (28 Days) Toxicity (Oral))
according to guideline
other: EPA OPPTS 870.3050
GLP compliance:
Limit test:

Test material

Constituent 1
Test material form:
other: Liquid

Test animals

other: CRL: CD(SD)
Details on test animals or test system and environmental conditions:
- Source: Charles River Laboratories Inc, Raleigh, North Carolina.
- Age at study initiation: ~ 7 weeks
- Housing: Stainless steel cages , one animal per cage.
- Diet (e.g. ad libitum): Ad libitum
- Water (e.g. ad libitum):Ad libitum
- Acclimation period: At least one week prioir to the start of the study.

- Temperature (°C): 22 ±1°C
- Humidity (%): 40 - 70%.
- Air changes (per hr): 12 -15 air changes per hour.
- Photoperiod (hrs dark / hrs light): 12 hours light/ 12 hours dark

Administration / exposure

Route of administration:
oral: gavage
corn oil
Details on oral exposure:

- Justification for use and choice of vehicle (if other than water): Test substance immiscible in water
- Concentration in vehicle: 7.5, 2.5, 75 and 125 mg/ml.
- Amount of vehicle (if gavage): Suspensions were administered at a dose volume of 4 ml/kg body weight.
Analytical verification of doses or concentrations:
Details on analytical verification of doses or concentrations:
Analysis of dose suspensions initiated on day 1 using LC-UV with external standards.
Duration of treatment / exposure:
Test duration: 28 days
Frequency of treatment:
Dosing regime: 7 days/week
Doses / concentrations
Doses / Concentrations:


No. of animals per sex per dose:
Male: 5 animals at 0, 30, 100, 300 and 500 mg/kg bw/day
Female: 5 animals at 0, 30, 100, 300 and 500 mg/kg bw/day
(50 animals in total)
Control animals:
yes, concurrent vehicle

Results and discussion

Results of examinations

Details on results:
Clinical observations: Mild and transient sedation, as evidenced by partial eyelid closure (both sexes) and decreased activity (females only) was noted during the first week in the 500mg/kg/day dose group. Secondary effects observed in both sexes in this dose group were; decreased faecal production, (which was also seen in the males in the 300mg/kg/day dose group) and variable incidences of perioral soiling. Transient perineal soiling was also observed in the females of in the 500mg/kg/day dose group. Perioral soiling (salivation) occurred throughout the study but this was thought to be a local response to the taste and/or smell of residual test material accidentally deposited in the oral cavity during the removal of the gavage needle following dosing. In males, at all dose levels, the body weights and the body weight gains were decreased relative to the control group. At the end of the study the cumulative body weight gains were recorded to be 5.4%, 19.4%, 10.9%, and 19% lower than controls in males dosed at 30, 100, 300 or 500mg/kg/day respectively. However, the result at 30mg/kg/day was biased by the result of one rat, which showed a reduced weight gain in week 2 only. Female body weight gains were unaffected.
During days 1-4 of dosing, the food consumption in both sexes was depressed in the 300 and 500mg/kg/day dose groups. Lower feed consumption was considered secondary to a mild sedative effect related to substance exposure. During the remainder of the study the food consumption values for animals dosed with 300 or 500 mg/kg bw/day were similar to the control. Animals fed 30 or 100 mg/kg bw/day showed no significant effect on food consumption.
Males animals showed no significant differences in the hematologic parameters.
Females dosed at 500 mg/kg bw/day showed a reticulocyte count higher than the controls but this was not identified as significant and was not considered treatment related.

Prothrombin Time:
There were no treatment related alterations in the prothrombin times of male or female rates observed.

Clinical Chemistry:
Statistically significant differences were identified in the levels of urea nitrogen, alanine aminotransferase, alkaline phosphatase, total protein, albumin and trigylcerides. None of the differences were considered to be treatment related.
No statistically significant differences were identified.

Effects in organs: In both sexes, at the two highest doses, increased liver weights and hepatocellular hypertrophy in the centrilobular/midzonal region of the hepatic lobule was observed. These changes were not accompanied by any evidence of degeneration or necrosis and, therefore, were interpreted as secondary to the induction of enzymes required to metabolise the test substance.

Effect levels

open allclose all
Dose descriptor:
Effect level:
100 mg/kg bw/day (nominal)
Basis for effect level:
other: original NCD unit is mg/kg/day.
Dose descriptor:
Effect level:
30 mg/kg bw/day (nominal)
Basis for effect level:
other: original NCD unit is mg/kg/day.

Target system / organ toxicity

Critical effects observed:
not specified

Applicant's summary and conclusion

Based on the results of the study and taking into consideration the comments made by expert toxicologist Dr G H Pigott subsequent to completion of the study, the no effect level (NOEL) is set at 100 mg/kg/day for females. The study directors proposal for an NOAEL of 30 mg/kg/day in males is considered unduly conservative. Based on a small decrement in bodyweight gain the lowest observed adverse effect level (LOAEL) in males is also set at 100 mg/kg/day.
Executive summary:

A GLP study was performed in accordance with OECD 407 in order to assess the effect of Inhibitor AHM P500 when administered to rats by oral gavage over a 28 day period.

Groups of five male and five female rates were dosed with 0, 30, 100, 300 or 500 mg/kg/bodyweight/day in corn oil daily for 28 days. Daily cage-side and clinical observations were made, in addition to weekly detailed clinical observations, ophthalmic examinations, body weights, feed consumption, haematology, clinical chemistry, urinalysis, organ weights and gross and histopathologic examinations .

Exposure to 500 mg/kg/day caused mild and transient sedation during the first week of the study. Secondary effects in males and females included decreased feces (also observed in the 300 mg/kg/day group), variable incidences of perioral soiling and transient perineal soiling (females only). Perioral soiling was thought to be a response to the taste and/or smell of the test substance on the removal of the gavage needle.

Body weights and body weights gains were decreased relative to controls in males given ≥30 mg/kg/day. Female body weights were unaffected by the test substance.

Feed consumption during the first week of the study was reduced in males and females given 300 or 500 mg/kg/day. 

Triglycerides were decreased in males dosed with ≥30 mg/kg/day. Alkaline phosphate activities of males dosed with ≥100 mg/kg/day were also decreased. Correlation of these differences was not observed in any tissues and the differences are believed to be secondary to the lower body weights. Increased liver weights and microscopic hepatocellular hypertrophy in the centrilobular/midzonal region of the hepatic lobule occurred in males and females dosed with 300 or 500 mg/kg/day.

These changes are attributed to be secondary to the induction of enzymes required to metabolise the test substance.

A NOEL was not determined for male rats; the NOAEL for male rats was 30 mg/kg/day. The NOEL for female rats was 100 mg/kg/day.

Subsequent re-evaluation of the study results and conclusions was performed by Dr G H Pigott. It was recommended that the LOAEL for male rats be set at 100mg/kg/day, with the NOEL for female rats retained at 100 mg/kg/day.

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