Read-across of 90-day rat oral repeated-dose toxicity: A case study for selected 2-alkyl-1-alkanols

- The category is limited to readily bioavailable 2-alkyl-1-akanols of intermediate size (C5 to C13).
- 2-Alkyl-1-akanols are toxicants acting via a simple narcosis mechanism.
- Toxicokinetically and toxicodynamically, the 2-alkyl-1-akanols are highly similar.
- 2-Ethyl-hexanol and 2-propyl-1-heptanol can be read across to other analogues with acceptable uncertainty.

2-Alkyl-1-alkanols offer an example whereby the category approach to read-across can be used to predict repeated-dose toxicity for a variety of derivatives. Specifically, the NOAELs of 125 mg/kg bw/d for 2-ethyl-1-hexanol and 2-propyl-1-heptanol, the source substances, can be read across with confidence to untested 2-alkyl-1-alkanols in the C5 to C13 category based on a LOAEL of low systemic toxicity. These branched alcohols, while non-reactive and exhibiting unspecific, reversible simple anaesthesia or nonpolar narcosis mode of toxic action, have metabolic pathways that have significance to repeated-dose toxic potency. In this case study, the chemical category is limited to the readily bioavailable analogues. The read-across premise includes rapid absorption via the gastrointestinal tract, distribution in the circulatory system and first-pass metabolism in the liver via Phase 2 glucuronidation prior to urinary elimination. 2-Ethyl-1-hexanol and 2-propyl-1-heptanol, the source substances, have high quality 90-day oral repeated-dose toxicity studies (OECD TG 408) that exhibit qualitative and quantitative consistency. Findings include only mild changes consistent with low-grade effects including decreased body weight and slightly increased liver weight, which in some cases is accompanied by clinical chemical and haematological changes but generally without concurrent histopathological effects at the LOAEL. These findings are supported by results from the TG 408 assessment of a semi-defined mixture of isotridecanols. Chemical similarity between the analogues is readily defined and data uncertainty associated with toxicokinetic and toxicodynamics similarities are low. Uncertainty associated with mechanistic relevance and completeness of the read-across is reduced by the concordance of in vivo and in vitro results, as well as high throughput and in silico methods data. As shown in detail, the 90-day rat oral repeated-dose NOAEL values for the two source substances can be read across to fill the data gaps of the untested analogues in this category with uncertainty deemed equivalent to results from a TG 408 assessment.