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EC number: 204-617-8
CAS number: 123-31-9
Subchronic dermal toxicity with
emphasis on aspects of nephrotoxicity and renal cell proliferation was
investigated in groups of 20 male and 20 female F344 rats with a test
protocol similar to OECD Guideline 411. Dermal application of 0, 2.0,
3.5, and 5.0% hydroquinone in an oil-in-water emulsion cream, comparable
to cream base of commercial cream preparations with HQ, was performed on
5 d/w, for 6 h/d during 13 w. Ingestion of test substance from the
application site was prevented using a semi-occlusive wrap, and during
periods without treatment by application of an Elizabethan collar.
Resulting dermal doses were 29.5, 51.9, and 73.9 mg/kg bw/d in male
rats, and 43.8, 77.0, and 109.6 mg/kg bw/d in female rats applied on a skin
surface area of 24 cm2 (dermal doses of ca. 1 to 4 mg/cm2).
In additional groups of 5 rats per sex, that had been treated for 3, 6
and 13 w, urinalysis data were collected and renal cell proliferation in
different proximal tubule segments (P1, P2, P3 and other cells) was
investigated via a BrdU incorporation assay. Dermal irritation was
scored by grading of the erythema and oedema scores according to Draize
(1959) daily during weeks 1, 2, 6, 7, 12, and 13. There was a
concentration-related increase of erythema in HQ-treated groups with
highest score of 2 throughout the course of the study. These effects
abated during treatment-free weekends. Consequently, there is no
indication that the maximal tolerable dose (MTD) was exceeded.
Dermal application of 5% HQ procuded
transient minor irritation of the skin but no evidence of exogenous
ochronosis. Up to the highest tested dose, there were no clinical signs
of intoxication, and no statistically significant or toxicologically
relevant changes of body weights, organ weights, of food and water
consumption, of haematological and clinical chemical parameters.
Treatment-related nephrotoxicity was not indicated from urinalysis data
and from kidney histology. There were no changes indicative of sustained
cellular proliferation in renal tubuli. Consequently, NOAELs in this
subchronic dermal toxicity study were 73.9 mg/kg bw/d in male rats, and
109.6 mg/kg bw/d in female rats.
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