Determination of LD50 of Phenobarbital

Points to be discussed

• Phenobarbital: MOA, SE

• LD₅₀

• Determination of phenobarbital LD₅₀

Lab work

Material:

Drugs:

• Phenobarbital (2%)

Animals: 48 mice.

Method:

1. The animals are weighed to the nearest gm. Then the mice are divided according to the animals weight into 6 groups (each group had 8 mice with equal weight distribution), the groups were labeled 1, 2,3,4,5, and 6.

2. Phenobarbital is injected intraperitoneally in different doses (according to the animal wt.) to the animals. Each group is given a certain dose per animal wt. (see table 1.).

3. After 24 hr. the number of dead animals in each group is counted and recorded in table 1.

4. LD₅₀ of phenobarbital is calculated by arithmetic and graphic methods

Table 1

Group	Dose (mg/kg)	Log dose	Dead	Dead %	Corrected %	Probit
1	330
2	300
3	280
4	250
5	220
6	120

*Correction formulas: for the 0% dead, 100(0.25/n). For the 100% dead, 100 [(n-0.25)/n], where n= number of animals in each group.

Table2. Phenobarbital toxicity in mice, computed by Karber method

- LD₅₀ = 330 – (T/8) = mg/kg

Category: Pharmacology Notes