Question

There is a antiviral drug with IC50 value for 1.63. However, the different EC50 values were recorded for MERS, SARS and CHIKV.

can you explain why there is the difference in EC50?

Answer 1

The EC50 is the plasma concentration of the rug that induces 50% change in response to the drug against the virus in test animals. This change in response can be stimulatory (for agonists) or inhibitory (drugs). Thus, EC50 is the concentration of the drug that gives half maximal response, between baseline and the maximal response in animals after exposure of the virus from specific time period. Thus, it is the concentration of drug that gives 50% response in the animals infected with each virus. The infectivity of the virus differs between animal to animal. It will depend on the immune response to the virus. Thus, EC50 will change for each virus. Some viruses have high infectivity while some have low infectivity. Hence, EC50 changes for different viruses such as MERS, SARS and CHIKV.

IC50 is the concentration of the drug to inhibit the 50% of biochemical or biological function in the virus. Hence, IC50 values are obtained from invitro studies where the known concentration of a virus will infect the cell line. The IC50 values will be same in the cell lines as no other factor are involved in limiting growth of these viruses. The IC50 value is the value that inhibits 50% of response to antigen-antibody binding. As the antigen-antibody response for MERS, SARS and CHIKV is same in the same cell line, the IC50 value will be the same for the three viruses.

EC50 values are obtained from in vivo studies while IC50 values are obtained for drugs from invitro studies.