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Neurotoxicity

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Description of key information

Only one 2 week neurotoxicity study is available, which has been conducted in the early seventies, i.e. prior to the implementation of technical guidelines for study conduct and at a time where GLP was not mandatory (Ciba-Geigy Ltd PH 2.632). The informative value of this study has to be considered with caution.

Key value for chemical safety assessment

Additional information

A 2-week neurotoxicity study was conducted with triclosan offered orally (unspecified) to rat a doses of 0, 100, 300, 1000, 2000 mg/kg bw/day (Ciba-Geigy Ltd PH 2.632). 17 deaths in high-dose group (5 of these were sacrificed due to moribund condition) as well as decreased body weights in the high dose group were reported. Dose-dependent inhibition of movement, decreased muscular tone, polydipsia and polyuria were reported at dose levels of 300 mg/kg bw/day and higher. Clinical signs were most severe in the high-dose group and also included spastic respiration for several animals. No difference in brain

weights between treated and controls (no other organ weights were measured). No histopathological changes in the brain or sciatic nerve of treated or control animals were observed (no other tissues evaluated).

The results of this study indicate a NOEL of 100 mg/kg body weight/day for triclosan in the rat. There was no evidence of neuropathology at any dose level, as examined in the brain and sciatic nerve tissues. The investigators concluded that triclosan produces no specific neurotoxic effects in the rat; however, the reasons for observations of clinical signs consistent with possible neurotoxicity (e.g., hypoactivity, decreased muscular tone) are unclear.

Moreover, it has to be noticed that triclosan bears no structural similarity to organophosphates, carbamates or other known inducers of delayed neurotoxicity, and acute and repeated-dose studies in several species did not indicate the occurrence of neurotoxic effects. Thus, the findings reported in the study above have to be considered with caution.

Justification for classification or non-classification

Since triclosan bears no structural similarity to organophosphates, carbamates or other known inducers of delayed neurotoxicity and since acute and repeated-dose studies in several species did not indicate the occurrence of neurotoxic effects, there is no need to classify triclosan.