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

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

Principle of the test

The test substance is administered orally (gavage) to adult rats, usually females, which are more sensitive in most cases. Administration is done sequentially: a single dose is given to one animal, then depending on survival or mortality, the dose is adjusted upwards or downwards for the next animal. The procedure continues until the LD50 can be statistically estimated, integrating 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 lesions. This dynamic approach limits the number of animals exposed to potentially lethal doses, meeting the 3R principles (Reduction, Refinement, Replacement) 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.
Biocides Regulation (BPR, EU No. 528/2012) and Plant Protection Products (EC Regulation No. 1107/2009): mandatory toxicological assessment.
UN and ADR transport: classification of dangerous 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 based on 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 compared to traditional methods.

YesWeLab Services

At YesWeLab, we support you in carrying out your acute oral toxicity tests according to OECD 425, via a network of rigorously selected partner laboratories, the majority of which are certified or accredited (ISO 17025, GLP/GLP, COFRAC). We guarantee you complete support for your analytical and regulatory needs, tests carried out in compliance with international guidelines (OECD, OCSPP, EC regulation 440/2008, CLP, UN ADR), the preparation and submission of IUCLID reports adapted to your regulatory dossiers (REACH, GLP, phytosanitary), centralized management via our digital platform to simplify your requests, sample tracking and receipt of results.

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