The efficient concentration at different times EC50,t (mg extract mg-1 DPPH•) is the amount of the extracts in relation to the amount of initial DPPH•, which calculated using the following equation:
EC50,t = IC50,t/[DPPH•]t=0
where IC50,t is the inhibitory concentration at different times, defined as the concentration of extract (mg mL-1) required to scavenge 50 % of DPPH• and [DPPH•]t=0 is the initial concentration of DPPH• (mg mL-1).
check this paper
http://www.doiserbia.nb.rs/ft.aspx?id=0352-51391200065S
IC 50 is half maximal inhibitory concentration and its a measure of the effectiveness of a substance in inhibiting a specific biological or biochemical function by half (e.g. inhibition of enzymes, affinity to cell receptors). In pharmaceutical research, it is a frequently used unit to specify the in vitro potency of a drug. For competition binding assays and functional antagonist assays IC50 is the most common summary measure of the dose-response curve
EC50 is when the half of ts maximal effect is observed. The EC50 of a quantal dose response curve represents the concentration of a compound .
The concepts of IC50 and EC50 are fundamental to pharmacology. The EC50 is the concentration of a drug that gives half-maximal response. The IC50 is the concentration of an inhibitor where the response (or binding) is reduced by half.
Seems simple enough. But when you actually go to fit data to determine these values, there are several complexities and ambiguities.
The rest of this article is about IC50 (I for inhibition, for downward sloping dose-response curves). All the ideas can be applied to stimulatory curves and EC50 (E for effective) as well.
Can IC50 and EC50 be same of the drug? Suppose if we plot the dose response curve using % cytotoxicity by MTT assay in case of death caused by virus, which is inhibited at various concentrations of drug? X axis involves virus alone and virus in combination with various concentration of drug and Y axis has % cytotoxicity. How to calculate IC50 and EC50 from this graph?
what will be the binding affinity of the drug if Ki value is more ?
Based on the two articles I have read, these have the same concept in the case of antioxidant properties. One of them has mentioned, "IC50 value is a concentration of a sample required to inhibit 50% of radical" (Molecules 2009, 14, 5349-53610). And another one has mentioned, "the EC50 is a concentration of a sample required to obtain a 50% antioxidant effect" (Food Chemistry Volume 138, Issue 1, 1 May 2013, Pages 414-420).
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