毒理学基础个人总结 Chapter 7 General Toxicity Studies

Chapter 7 General Toxicity Studies

General Considerations

Acute

≤24-h (single or repeated administrations)

Subchronic

≥3-m in rats or 1-2y in dogs (up to 10% of life span, repeated administrations) Chronic

18-m in mice, 24-m in rats, or 7-10y in dogs and monkeys (entire/major life-span) Part 1 Acute Toxicity Studies

Basic Conception

•One or more routes of administration, and one or more species of laboratory animals are used.

•Within 24 h of exposure duration

•14 d for observation, to make sure all possible toxicity can be assessed.

•Toxic effects: Mortality, signs of intoxication, behavioral modifications, morbidity, etc.

Objectives and Parameters of Studies

1.Objectives

Quantitative estimation of acute toxicity (LD50); target organs and other

clinical signs; reversibility; a basis of dosing for further studies.

monly Used ParametersMedian

lethal dose (LD50), median lethal concentration (LC50, for inhalation), with 95% confidence limits, values affected by many factors related to the

experimental conditions (p185).

Experimental Design

1.Selection of Animal Species

•Mouse and rat most often used, suitable for both inhalation and oral toxicity test (preference is rat, but mouse is more economical).

•At least 5 d for acclimatizing the animals to the lab environment, at least 5 animals at each sex per dose level, females should be nulliparous and

non-pregnant

2.Route of Administration

•The main routes for xenobiotics to enter the body: GI tract (ingestion), lungs (inhalation), and skin (dermal).

•By ingestion: in diet, in drinking water, by gastric gavage, or by gelatin capsules.

•By inhalation: using inhalation exposure chambers (static or dynamic)

•Dermal administration:

•By i.p., i.m., i.v., s.c., intradermal injection

3.Dosage and Experimental Groups

•Four or more doses are required for a classic LD50 determination.

•At lease 3 doses “effective”

•Low≥ 10

•Middle≈ 50

•High≤ 90

•To improve the precision of LD50 (for a narrow confidence range)

a.By increasing the number of animals per dose

b.By decreasing the ratio between successive doses (ordinarily 1.2—1.5)

4.Observation and Examination

•Duration of observation, typically 14 d, but not fixed to this length of time.

Extended observation should be done when necessary , especially delayed

death is expected.

•Careful clinical examination, at least once each day, particular attention to tremors, convulsion, salivation, diarrhea, lethargy, sleep and coma; Time of

death (precise); necropsy done for dead animals and at the end of

observation.

Alternative Methods of Acute Toxicity Tests

•In order to reduce the number of test animals or refine procedures to make exposures less stressful to animals, alternative methods of acute toxicity tests have been explored, and several of them have been adopted by OECD (Organization for Economic Cooperation and Development).

1.Fixed Dose Procedure

•Its main study involves non-lethal effect s.

• A sighting study is a preparation of the main study, searching for an appropriate dose for the latter.

•Sighting study starts from a fixed dose, taken from the following levels, 5, 50, 300, 2000, and rarely 5000 mg/kg, according to the related literature about

the chemical.

•Five animals per sex are required for a main study.

• A dose producing some signs of toxicity without severe toxic effects or death is expected from the main study.

•The tested chemical is then classified according to the Globally Harmonized System of Classification and Labeling of Chemicals (GHS).

2.Acute Toxic Class Method

• A stepwise procedure with 3 animals in the first step.

• A group of animals receive one of the following doses: 5, 50, 300, 2000 mg/kg.

•Depending on the resultant mortality, in the next step experiment three or more animals may receive the same or higher or lower dose.

•2-4 steps may be carried out before allowed for judgment of acute toxicity.

•Biometric evaluation on the obtained data to find a proximate LD50 value, then classification of a substance is done according to GHS.