Determination of LD 50 LETHAL DOSE 50 LD

Determination of LD 50

LETHAL DOSE 50 (LD 50) The amount of a toxic agent (as a poison, virus, or radiation) that is sufficient to kill 50 percent of a population of animals usually within a certain time Expressed as milligrams of substance per kilogram of body mass Compare the toxic potency or intensity of different chemicals A measure of acute toxicity

LETHAL DOSE 50 (LD 50) A 10 mg causes kidney toxicity B 10 mg causes neuro toxicity Which drug is more toxic? LD 50

SIGNS RECORDED DURING ACUTE TOXICITY STUDIES increased motor activity, stimulation, hyperesthesia tremors, arching and rolling, clonic convulsions, tonic extension, lacrimation, sedation, , hypnosis, cyanosis Straub reaction muscle spasm, writhing, loss of righting reflex, ataxia

DIFFERENT METHODS FOR THE DETERMINATION OF LD 50 § For research purpose, the most widely used method is Litchfield and Wilcoxson § For routine practical class work; Reed-Muench, Miller-Tainter and Karber’s Method Arithmetical method: Karber method Graphical method: Miller and Tainter

DIFFERENT METHODS FOR THE DETERMINATION OF LD 50 For calculating LD 50 by any one method: § Find out the least tolerated (smallest) dose (100% mortality) and most tolerated (highest) dose (0% mortality) § Once these two doses are determined, select at least 5 doses in between them, and observe mortality due to these doses § The percentage mortality values are converted to probit values by reading the corresponding probit units from the probit table § Plot the probit value against log doses and read LD 50 value as the dose that corresponds to probit

Probit Values Probit table aids other researchers to convert their kill percentages to his probit, which they could then plot against the logarithm of the dose and thereby, it was hoped, obtain a straight line Such a so-called probit model is still important in toxicology, as well as other fields

OBJECTIVES General Objective: § To determine the Median Lethal Dose of neostigmine introduced on mice intraperitoneally Specific Objectives: § To determine the number of deaths per dose of neostigmine one hour after intraperitoneal administration § To determine the LD 50 of neostigmine using the Miller -Tainter method § To compare the experimentally determined LD 50 to theoretical standard of LD 50

MATERIALS AND METHODS 60 mice, approximately same weight Neostigmine 0. 5 mg/ml injections

60 MICE MATERIALS AND METHODS 10 10 10 DIFFERENT DOSAGES (IN GEOMETRIC INCREMENT) PER Kg 0. 1 mg 0. 2 mg 0. 4 mg 0. 8 mg 1. 6 mg 3. 2 mg

MATERIALS AND METHODS The number of dead mice, within an hour was counted (% dead) Abnormal behaviors, tremors and seizures were observed and noted The rationale for using the geometric dosage sequencing is that this is more cost-efficient and allows experimenters to see the effect without sacrificing too many animals

RESULTS Apply correction factor to 0% and 100% mortality group [for 0% dead = 2. 5% and for 100% dead = 97. 5%] % Response conversion to Probit Units by the Probit Transformation Table Convert Doses to log Dose (log 10 dose = x) The probit value and the percentage of deaths against log dose are plotted

RESULTS Sample Probit Computation For the 20% response 20% = 4. 16

RESULTS Sample Probit Computation For the 2. 5% response 2. 5% = 2. 95 + 3. 12 = 3. 035 2

PLOT % RESPONSE PROBIT UNITS LOG DOSE

LINEAR REGRESSION

RESULTS From the regression of the probit-log dose line, the log dose was extrapolated corresponding to probit units of 5 The extrapolated dose corresponds to the median lethal log dose, and the antilog of this log dose value would be the LD 50 value The dose corresponding to 50% or probit 5 was taken as LD 50

LIMITATIONS OF LD 50 The LD 50 gives a measure of the immediate or acute toxicity Results may vary greatly LD 50 is not tested on humans The LD 50 test is neither reliable nor useful Because the human lethal dose is difficult to be predicted from animal studies