Acute oral toxicity – OECD 425 test (Dose adjustment method)

OECD Guideline 425 describes a method for assessing the acute oral toxicity of a substance in rats. It is based on a sequential Up-and-Down Procedure (UDP), which allows for the estimation of the LD50 (median lethal dose) while significantly reducing the number of animals used compared to traditional (OECD 401) or alternative (OECD 420 and 423) methods. The method is designed to provide reliable information on acute systemic effects after ingestion, necessary for classifying substances according to the Globally Harmonized System (GHS/CLP) and for regulatory requirements such as REACH, the Biocidal Products Regulation (BPR), the Phytosanitary Regulation, and UN transport regulations.

Principle of the test

The substance being tested is administered orally (gavage) to adult rats, usually females, which are more sensitive in most cases. Administration is sequential: a single dose is given to one animal, then, depending on survival or mortality, the dose is adjusted up or down for the next animal. This procedure continues until the LD50 can be statistically estimated, incorporating confidence intervals. The animals are observed for up to 14 days to detect clinical signs of toxicity, mortality, or delayed effects. Autopsies may be performed to identify associated organ damage. This dynamic approach limits the number of animals exposed to potentially lethal doses, adhering to the 3Rs (Reduce, Refine, Replace) principles in animal experimentation.

Applications and regulatory framework

GHS/CLP classification: assignment of the substance to an acute toxicity category.
REACH compliance (EC No. 1907/2006): requirement for the registration of chemical substances.
Biocidal Products Regulation (BPR, EU No. 528/2012) and Plant Protection Products Regulation (EC No. 1107/2009): mandatory toxicological assessment.
UN and ADR transport: classification of hazardous substances for transport.
Risk assessment in the context of human health and occupational safety (safety data sheets, labeling).

Comparison with other OECD methods

OECD 420 (Predetermined Dose): assesses toxicity from fixed doses (5, 50, 300, 2000 mg/kg), without direct calculation of LD50.
OECD 423 (Acute Toxicity Class Method): provides a classification into acute toxicity categories, but not a numerical LD50 value.
OECD 425 (UDP): allows estimation of LD50 with confidence intervals, while reducing the number of animals required compared to traditional methods.

YesWeLab Services

At YesWeLab, we support you in conducting your acute oral toxicity tests according to OECD 425, through a network of rigorously selected partner laboratories, most of which are certified or accredited (ISO 17025, GLP, COFRAC). We guarantee comprehensive support for your analytical and regulatory needs, from tests performed in compliance with international guidelines (OECD, OCSPP, EC Regulation 440/2008, CLP, UN ADR), to the preparation and submission of IUCLID reports tailored to your regulatory dossiers (REACH, BPR, plant protection products), centralized management via our digital platform to simplify your requests, sample tracking, and results receipt.

Related analyses

OECD 420 – Acute oral toxicity (Predetermined dose method)
OECD 423 – Acute oral toxicity (Acute toxicity class method)
OECD 402 – Acute dermal toxicity
OECD 403 – Acute inhalation toxicity