Phenothiazine

Endpoint summary

Additional information

Additionally to the bacterial reverse mutation tests (Ames tests) reported as part of this registration dossier, there are several other studies available in the literature, none of which indicated any positive result in this assay.

Regarding mutagenicity to mammalian cells some contradictory study summaries were found. Four studies, which were only available as an abstract indicated that four different qualities of phenothiazine were all negative in the mouse lymphoma assay. One further study indicated that under certain conditions an increased number of mutants was found. However, none of these five studies was available as a full study report, hence making it not possible to reliably identify the most relevant study. In a newly conducted OECD 476 study it was found that under certain conditions (i.e. without metabolic activation, 4 hrs exposure) a weak, yet dose-dependent increase in mutants was found. However, the absolute number of mutants generally was in the range of the historical controls of the facility. The relative increase was only slightly above the threshold of 2, which is indicative for a mutagenic effect. Additionally, two further phenomena were observed: i) precipitation of the test item and ii) phenothiazine exhibited a high cytotoxicity, beginning at concentrations of 2 mM and persisted up to 10 mM representing the highest concentration tested. Mutagenicity as indicated by slightly exceeding the threshold of 2 was found at the two highest concentrations only. Relative total growth decrease to about 10 -20 % for these concentrations, hence making cytotoxicity quite apparent. To secure this finding, a repetition experiment considering long-term exposure (in accordance with OECD 476) was conducted. In the repetition experiment the threshold of two was not exceeded for the cells exposed to phenothiazine (without metabolic activation). Also, with metabolic activation no indication for an increased rate of mutations was found that could be attributed to phenothiazine exposure.

One study on cytogenicity was partly available to the consortium. Here, effects of phenothiazine on sister chromatid exchange were assessed. As a result it was found that phenothiazine induces sister chromatid exchange either with or without metabolic activation. However, the study is only partly available not allowing a conclusive decision on reliability. Additionally, possible clastogenic effects due to phenothiazine exposure were examined in an in vivo assay conducted at the NTP. Here, sufficient data to judge reliability is available. As a result no indication for clastogenicity due to phenothiazine exposure was found. Following the guidance given by ECHA a negative in vivo result overrules a positive in vitro finding.

Short description of key information:
Bacterial reverse mutation test (Ames test)
- Two NTP-studies were available
- Studies conducted according to GLP and recent NTP-protocols
- Result: negative

In vitro mammalian cell gene mutation test (mouse lymphoma assay)
- Study conducted according to OECD 476 and GLP
- High cytotoxicity was observed with and without metabolic activation
- In one subset a weak yet dose dependent increase in mutants was found
- However, the absolute number of mutants was generally within the range of historical controls. In the repetition experiment with long-term exposure (24 hrs) this increase was not found again.
- Result: equivocal

In vivo micronucleus
- Study conducted according to GLP and recent NTP-protocol
- Bone marrow was evaluated
- Result: negative

Endpoint Conclusion: No adverse effect observed (negative)

Justification for classification or non-classification

Based on the present studies available classification of phenothiazine as genotoxic according to the provisions laid down in Commission Regulation (EC) No 1272/2008 is not justified.