Initial Safety Assessment Using Single-Dose Toxicity Study (Acute Toxicity)

This article explains the importance of single-dose toxicity testing (acute toxicity), evaluation items, and the differences between it and repeated-dose toxicity testing.

The importance of single-dose toxicity studies (acute toxicity studies)

Single-dose toxicity studies (acute toxicity studies) are non-clinical studies that involve administering a drug candidate or other substance to animals only once to investigate toxic reactions and lethality that occur within a short period (usually 14 days). The main purpose of this study is toEstimation of lethal dose and maximum tolerated dose (MTD), and identification of target organsThis is. By conducting tests, it is used as a basis for predicting human overdose and for occupational safety and health.

The main evaluation items obtained from a single-dose toxicity test

Observation of toxic symptoms and identification of target organs

During the test period, closely observe the general condition of the animals (behavior, weight change, intake, etc.).Accurate recording of the timing from the onset of toxic symptoms to recovery or death.After the examination is completed, an autopsy (pathological autopsy) is performed, and further pathological histological examination is conducted throughIdentification of the organ that the substance showed toxicity to (target organ)This will be performed. The data obtained at this time will serve as important monitoring indicators for the next stage of testing.

Estimation of approximate lethal dose and maximum tolerance level

In past acute toxicity tests, a strict calculation of the lethal dose for 50% of the population (LD50) was required. However, currently, the perspective of animal welfare (3Rs) is emphasized,The mainstream method is to estimate the "approximate lethal dose (ALD)," which indicates the approximate dose that leads to death with the minimum necessary number of animals for testing, and the "maximum tolerated dose (MTD)," where toxicity is tolerable without death.It is.

Difference from repeated-dose toxicity studies

Difference between number of doses and evaluation period

Each exam,The administration conditions and evaluation targets are different.In a single-dose toxicity study, a substance is administered only once, primarily to evaluate acute toxic responses and lethality over a short period, typically about two weeks. In contrast, repeat-dose toxicity studies involve daily administration over several weeks to months (or even longer in some cases) to assess cumulative and chronic toxicity.

Role as a bridge to the next phase of testing

A single-dose toxicity study does not prove safety on its own, but rather serves as a bridge to properly conduct subsequent repeated-dose toxicity studies. The maximum tolerated dose and toxicity data obtained from a single-dose study...The essential basis for setting the dosage (determining high, medium, and low doses) in subsequent repeated dose toxicity studiesIt will be.

Key points for guideline-based test design

Animal species selection and route of administration

In test design,Efforts are needed to enhance extrapolation to humans.For example, when selecting animal species, it is recommended to use two or more species, including non-rodents such as dogs and monkeys, in addition to rodents like mice and rats. It is also important to establish administration routes that are planned for future human clinical trials (e.g., oral, intravenous, transdermal) to obtain data that is relevant to practice.

Compliance with PMDA and ICH Guidelines

To conduct an Investigational New Drug (IND) or New Drug Application (NDA) for a new drug, it is necessary to meet the standards set by regulatory authorities in each country. In Japan,We will conduct tests in accordance with the guidelines of the Pharmaceuticals and Medical Devices Agency (PMDA) and the International Council for Harmonisation of Technical Requirements for Pharmaceuticals for Human Use (ICH) guidelines agreed upon by Japan, the United States, and Europe.This is what is required, and from this standpoint, we need to gather internationally acceptable data.

Criteria for selecting a CRO for single-dose toxicity studies

GLP Compliance Operational Results

When outsourcing trials to an external CRO, they are subject to strict regulatory inspections (audits), soIt is an absolute requirement that the study be fully compliant with GLP (Good Laboratory Practice).This is what it amounts to. Regarding this part, it can be said that it is important to confirm the history of past inspections and the functionality of the Quality Assurance Unit (QAU) which guarantees the reliability of data, in order to ascertain whether a high-quality control system is being maintained.

Commitment to animal welfare (3Rs) and proposal capabilities

In the current examination,Consideration of the 3Rs (Replacement, Reduction, and Refinement) is essential in animal experimentation.This is why a CRO is needed that can propose study designs to maximize data extraction with a smaller number of animals. Key factors in choosing a CRO include their high level of awareness regarding animal welfare, such as whether they have obtained full accreditation from AAALAC (Association for Assessment and Accreditation of Laboratory Animal Care International), and their flexible consulting capabilities in line with guidelines.