Reference no: EM133027354

FSCI Lab - Determination Of The Median Lethal Dose (Ld₅₀) Of A Drug

Introduction - All drugs are potentially dangerous and are capable of producing unwanted effects if given in sufficiently large amounts. The main objective of toxicity testing is to determine to nature of these effects in animal experimentation. The LD50 (i.e., when the effect measured is death in 50 percent of experimental animals) is determined from experiments on as many species of animals as possible. Tests employing rats and mice are common because these animals are inexpensive, and easy to handle, house and feed.

Aims and Objectives - This experiment will enable you to determine acute toxicity of pentylenetetrazol in laboratory mice and help you to:

i. Understand the quantal dose-response relationship when the end-point is death.

ii. Determine the median lethal dose (LD50) of pentylenetetrazol in a group of 50 male mice.

iii. Determine graphically LD50 of PENTYLENETRAZOL.

iv. Develop some observational skills in connection with the response of mice to convulsant drugs.

Methods -

i. Choose a single strain of white mice.

ii. Withhold food from animals for 12 hours prior to the beginning of the experiment, but give water freely.

iii. On the day of experiment divide the mice into five groups of ten animals per group, placing each group in a separate cage.

iv. Weigh and mark each animal for identification. Record the weight of each mouse in your laboratory notebook, keeping each group separate.

v. Calculate the dose range as follows: Assume that the LD50 lethal dose of pentylenetetrazol is a dose between 30 mg/kg and 90 mg/kg and calculate the doses between these two.

vi. Calculate the amount of pentylenetetrazol (Metrazol) to be given intraperitoneally and make the corresponding dilution from the stock solutions (if necessary).

vii. Inject each animal with a requisite amount of drug.

viii. Observe the mice for the following effects: The pattern and rate of respiration, presence or absence of feces (defecation), urination and palor, that is, whether there is flushing due to vasodilation (best seen in ears). Observe the mice for signs of either CNS stimulation due to hyperactivity or CNS depression which may result in sleep, paralysis especially of the fore and/or hind limbs, irritation in the gastrointestinal tract (such as in the stomach, characterized by writhing). Take note of any unusual positioning of the tail such as "Straub Tail Phenomenon," a condition in which the animal holds its tail perpendicular to its body.

ix. Record the number of mice that die per group within 24 hours and record the results.

Results -

1. Describe the signs of toxicity seen in the mice.

2. Use the results of mortality obtained to determine the median lethal dose by plotting the probit values against the logarithm of doses administered.

Data from Pentylenenetetrazol-Induced Convulsion in Mice

Discussion -

3. Why would a forensic toxicologist need to do acute toxicity testing in animals?

4. What are 3 advantages of using standardized methods in toxicology?

5. What is meant by the LD50 and state its significance.

6. Briefly discuss the Arithmetic Method of Reed-Muench.