OECD TG 423 is the standard “Acute Oral Toxicity – Acute Toxicity Class Method, ” i.e., acute oral toxicity—acute toxicity class method, which is listed in Section 4 (Health Effects) of the OECD Test Guidelines for the Testing of Chemicals. It was first adopted in 1996 and updated in 2001. The test is an in vivo toxicity test designed to evaluate the acute toxic effects of a substance following a single oral administration.
The main objective of OECD TG 423 is to determine the substance’s acute oral toxicity potential and its GHS/CLP classification, using fewer animals and prioritizing animal welfare compared to the traditional LD50 determination approach. The method uses fixed doses and a staircase design; rather than determining an exact LD50 value, it aims to identify the toxicity class to which the substance belongs.
The basic principle of the test is as follows:
- The test substance is administered orally to the animals at specific fixed doses (typically 5, 50, 300, and 2,000 mg/kg body weight).
- Three animals (usually female rats) are typically used per dose level; depending on the results, additional animals may be added or the study may proceed to the next dose level.
- Administration is typically performed in rats, as a single dose and in a suitable vehicle.
- The animals are kept under clinical observation for at least 14 days; during this time, signs of toxicity, reversibility, changes in body weight, and mortality are recorded.
- At the end of the study, a necropsy is performed and the macroscopic findings are documented.
- Thanks to the stepwise trial design, it is not necessary to test all dose levels; depending on the observed mortality rate, the trial proceeds to the next higher or next lower dose level.
The key features of the process are:
- Fixed dose levels: 5, 50, 300, and 2,000 mg/kg
- Staircase design: Switching between dose levels based on the mortality response
- Starting dose: Selected based on available data and structural similarities; 300 mg/kg is generally preferred as the starting dose
- Reduction in the number of animals: Compared to traditional LD50 tests, significantly fewer animals are used
- GHS/CLP Classification: The mortality data obtained are used to determine the acute oral toxicity categories
The main parameters reported in the study are as follows:
- The dose levels administered (mg/kg) and the number of animals per dose level
- Clinical observations and their onset
- Changes in Body Weight
- Mortality and Survival Times
- Autopsy Findings
- GHS/CLP Category for Acute Oral Toxicity and Rationale for Classification
- Estimated LD50 range (no exact value)
- Animal species used, sex, age, route of administration, and conditions of use
- Data on Measurement Uncertainty and Repeatability
Why is it performed?
OECD TG 423 is being conducted for the following scientific and regulatory purposes:
- Determination of Acute Oral Toxicity: Identification of Toxic Effects and Target Organs Following a Single Oral Exposure
- GHS/CLP Classification: Determination of the substance's acute oral toxicity category and establishment of labeling requirements
- Prioritization of animal welfare (3Rs): Reduction in the number of animals used compared to traditional LD50 tests and limitation of severe pain and suffering
- Support for Regulatory Filings: Use in Safety Assessments of Chemicals, Pesticides, Biocidal Products, Drugs, and Medical Devices
- Contribution to Risk Assessment: Provision of Baseline Data for Risk Assessment in Acute Exposure Scenarios
- Prioritization: Reviewing a large number of substances and setting priorities for further testing
- Labeling and Transportation: Data on acute oral toxicity are used in the classification of chemicals for labeling and transportation purposes
- Evidence-Based Approach: A Contribution to the Holistic Assessment of the Substance in Conjunction with Other Toxicological, Physicochemical, and Exposure Data
OECD TG 423 is not intended to determine a definitive LD50 value; instead , it provides a classification based on graded mortality data. The results should be interpreted in the context of the substance’s chemical structure, other acute toxicity data (e.g., TG 420, TG 425), repeated-dose toxicity, and exposure assessment.
As part of our nano-testing services, we conduct acute oral toxicity studies in accordance with OECD TG 423, applying scientific rigor and utilizing our accredited laboratory infrastructure and quality management system. Our scope of services includes the following:
Study Design and Protocol Development
Preparation of a test report in accordance with OECD TG 423
Scientific rationale for the initial dose and the stepwise dosing regimen based on the physicochemical properties of the test substance and the available toxicity data
Selection of a suitable vehicle and evaluation of solubility and stability; determination of animal species, sex, age, and administration conditions; compliance with ethical approval and animal welfare requirements; planning of a stepwise experimental design to minimize the number of animals
For information on study design, selection of the initial dose, suitability of the vehicle, sample collection conditions, the timeline, and reporting procedures for your acute oral toxicity studies in accordance with OECD TG 423, please feel free to contact Nano-Test.