Bioassay

Bio-living, assay-test
It is the process of determining the potency of the drug by using a suitable biological system like animals, tissues, microbes, etc.

PRINCIPLE OF BIOASSAY

To compare the test substance with the International Standard preparation (IP, BP, USP) of the same.
To find out how much test substance is required to produce the same biological effect as produced by the standard.

APPLICATION

To determine the potency of a drug.
To determine the dose of a drug required to produce a therapeutic or toxic response (ED₅₀, LD₅₀).
This process is used in the development of new molecules or their preparation.

CHARACTERISTICS OF A GOOD ASSAY METHOD

Sensitivity
Specificity
Repeatability
Reproducibility
Precision
Accuracy
Stability—tissue has to stay “bioassay-fit.”

BIOASSAY CAN BE PERFORMED ON:

In-vivo → Intact animal
In vitro → isolated tissues, specific cells, organisms.
WHOLE ANIMALS
1. Nor Adrenaline – Spinal Cat
1. Cardiac Glycosides – Guinea Pig
1. Insulin—Mice
1. Estrogens—Ovariectomized Female Rat
MICROORGANISMS
1. Vit B12 – Euglena gracilis
1. Tetracycline – Bacillus pumilus
ISOLATED TISSUE
1. Acetylcholine
1. – Frog Rectus Abdominus muscle
1. Histamine – Guinea Pig Ileum
1. Adrenaline—Rat uterus
1. Oxytocin—Rat uterus oestrogen primed
DISPERSED CELLS
1. Plasma LH estimation by stimulation of testosterone synthesis – on isolated Leydig cells

TYPES OF BIOASSAY

There are mainly two types of bioassays:
- Quantal assay
  - Direct end point assay (DEPA)
  - LD₅₀ determination
- Graded assay
  - Matching
  - Bracketing
  - Interpolation
  - Multiple points
    - Three-point
    - Four-point
    - Six-point
  - Cumulative dose response

QUANTAL ASSAY

The response is in the form of “all or none,” i.e., either no response or maximum response. Drugs producing a quantal effect can be bioassayed by the endpoint method.
The threshold dose producing a predetermined effect is measured
Comparison between the results of the standard and the test
E.g., bioassay of digitalis in cats, insulin-induced hypoglycemic convulsions in rats.

GRADED ASSAY

The response is proportional to the dose, and the response may lie between no response and the maximum response.

MATCHING OR BRACKETING

A constant dose of the standard is bracketed by varying doses of the test sample.
until an exact matching between the response of the standard & that of the test sample is matched.
The strength of unknown/test drug can be found by simple interpolation of bracketed response

ADVANTAGES

Simple & faster method.
The amount of test drug available is small
Does not involve complicated calculations
Does not depend on DRC

DISADVANTAGES

less accurate
Time-consuming
Cannot get exact match of response
Quantitative difference between the test & standard not obtained.

INTERPOLATION ASSAY

The concentration of the test drug is interpolated from the dose-response curve graph (DRC).
The DRC of the standard drug is plotted first, and then the different concentrations of the test drug are plotted.
The dose of the test drug, which comes at the linear log dose-response relationship, is interpolated from the dose-response plot.

Dr. Smrutiranjan Dash

With a foundation in pharmacology, I am engaged in both teaching and research. My work has been published in reputed national and international journals, and I actively participate in scientific conferences to share findings and stay connected with emerging advancements. Thank you for visiting. Your interest is truly appreciated.

BIOASSAY