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Let's look at a response versus log ligand curve for a full agonist. We can read the potency of this molecule off of our x-axis. The y-axis gives us the response. The vertical change. in the response is related to the efficacy of the molecule. An important idea from this graph is that potency is not the same as efficacy. Potency is the x-axis. Efficacy is the change on the y-axis. A molecule can have a high efficacy but low potency. A molecule can have high potency but low efficacy. Ideally a drug would have both high potency and high efficacy. The words efficacy and potency are often used interchangeably, but they do not have the same meaning. Efficacy for an agonist means the molecule is turning on a receptor pathway. The goal of the molecule, however, is to treat a disease. Just because a molecule shows high efficacy and high potency does not mean the molecule will be effective in treating a disease. This is an important idea. The efficacy against the disease is not measured until phase 2 clinical trials. This is a real risk in drug discovery, and it explains why so many molecules fail in phase 2 clinical trials. In order to minimize failure risks, drug companies look continuously to try to establish the value of a target for affecting the disease. This process is called target validation. Making sure that the binding between a drug and a target with a molecule will yield a therapeutic benefit in humans. Target validation may involve monitoring different molecules in the blood of animals during the animal studies. The monitored molecules are called biomarkers. Biomarkers are any molecule that can be measured. Biomarkers include anything from blood sugar or insulin to cholesterol or hormones. Researchers analyze biomarkers to establish that the target protein, when bound by a drug, is in fact having a positive systemic effect on a disease. Biomarkers help connect the potency and efficacy of a molecule in a binding assay to its therapeutic value in patients.

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