Principles of BIOASSAY
Burn and Dale articulated certain principles for conducting biological assays. These principles should be followed to derive effective results.
All bioassays (toxicity studies, laboratory studies, and clinical trials) should be relative against a standard drug or formulation. In this way, errors due to biological variation in bioassays can be reduced , as the new sample is concurrently compared with standard formulations.
Standard Preparations (Reference Standards): A standard preparation is a representative of the substance based on which the activity is comparatively measured. The se standard preparations are delivered to experts, pharmaceutical industries, and research laboratories for standardising new batches of productions.
These reference standards are upheld and distributed within India by the Central Drug Research Laboratory, Calcutta, and the Central Research Institute, Kasauli. They are controlled by U.S Pharmacopoeial Authorities in U.S.A , and by the National Institute of Medical Research, London , in Great Britain . They are also maintained and distributed to different laboratories by the Expert Committee on Biological Standardisation made by the WHO.
A unit is a certain weight of one of these standard preparations which creates a
definite effect in terms of the preparation under test.
The standard and the new drug should be quiet indistinguishable from each other. If so, their dose-response curves will also be similar and parallel, i.e., the potency ratio will be constant all along the response levels. But, this statement will stand invalid if the curves are not parallel.
The procedure for comparing the unknown with the standard drug should ideally (not essentially) test the therapeutic properties of the drug. In an ideal situation, an analgesic should be checked for its analgesic activity, and an anticonvulsant should be checked for its anticonvulsant activity. But, it is not always achievable, e.g., for insulin dropping of blood glucose would be the preferable potency index, but the frequently used method is mouse convulsion method, where the per centage of mouse developing convulsions is matched with the standard and new insulin.
The procedure should assess and allow an approximation of the errors because of biological diversification in various animals/persons at any given time and in the same animal/person at different times. The measures undertaken for minimising errors due to biological variations include:
1) The experimental conditions should be kept constant.
2) The biological response (indicator) should be sensitive to the drug.
3) The biological response (indicator) should be insensitive to other drugs.
4) The biological response (indicator) should give constant and reproducible results.
5) A standard preparation formulation (of known concentration ) should be
available for comparing the response.
6) Large number of experiments and assays should be conducted for minimising biological variation, and
7) Animals of the same species and st rain (ideally litter mates) , of equal age,
weight and gender, consuming equivalent diet and sheltered in same conditions should be used for performing experiments . I n some bioassay designs, cross-over of animals getting the sample and standard may occur.
Briefly, the sources of error in bioassays are primarily of two types:
1) Errors due to biological variation, and
2) Errors due to faulty methodology.