What is "counterscreening"

Screening \Screen"ing\ (skr[=e]n"[i^]ng), n. the process of examining or testing objects methodically to find those having desirable properties. See screen[3].

Note: In the pharmaceutical industry, pharmaceutical screening involves testing a large number of samples of substances to find those having desirable pharmacological activity; those samples which have the property sought are called active or positive in the screen. The substances tested may be pure compounds with known structure, mixtures of pure compounds, or complex mixtures obtained by extraction from living organisms. There are often additional sets of test performed on active samples, called

counterscreening to eliminate those samples that may also possess undesirable properties. In the case of screening of mixtures from living organisms, a type of counterscreening called dereplication is usually performed, to determine if the active sample contains a known compound which has previously been studied.

Dereplication \De`rep*li*ca"tion\, n. (Biochem.) the process of testing samples of mixtures which are active in a screening process, so as to recognize and eliminate from consideration those active substances already studied; -- a stage subsequent to the preliminary screening in the process of discovery of new pharmacologically active substances in mixtures of natural products; -- also called counterscreening. See screening.

Note: In the process of pharmaceutical screening (testing a large number of substances to find those having desirable pharmacological activity), the testing of samples of substances extracted from living organisms (plants, microorganisms, etc.) often detects substances already detected in prior screening. Such ``known'' or ``replicate'' activities must be recognized at an early stage to avoid duplicating previous efforts at purification and structural identification. The process of testing an sample which is active in a primary screen, to determine if the activity is due to a previously known substance, is called dereplication or counterscreening.