Potency, Efficacy and Therapeutic Index

What are Quantal Studies

Studies based on patient’s Yes/No response in order to determine a medication’s efficiency

What is ED50 (Quantal)

dosage required that allows 50% of the total number of patients surveyed to feel its therapeutic effect

How do you determine ED50 on a parabolic vs a logarithmic graph?

Parabolic: Look at the apex of the graph ; look at x axis to find dosage (the ED50)

Logarithmic: ED50 should appear at the middle area of the logarithmic graph, value should be shown on y-axis OR determine inverse log of x value at logarithmic graph midpoint

What is TD50? What is it also known as?

TD50: Toxic Dose 50%, or (not recommended) Lethal Dose 50%

What is the therapeutic index? How do we determine the therapeutic index?

1. Used to determine how many times more the patient can take a drug before they start displaying toxic symptoms

   1. Formula: TD50 / ED50 = Therapeutic Index

What can the values of a therapeutic index tell us?

Higher Index = Larger the buffer before going past therapeutic concentration range, safer the drug is (its the opposite for lower index)

What are Dose-Response Curves? What kind of curve is it

1. Used to determine the magnitude of the biological effect of a drug

2. Logarithmic curve

What is phase 1, 2 and 3 on the dose response curve?

Phase 1: Dose has limited/no effect on target cells

Phase 2: Linear response between dose and patient response

Phase 3: Patient response has plateaued; further administration of drug can cause adverse effects

What is potency?

The affinity of the drug and its receptor

What is efficacy?

Ability of drug to exert 100% of its biological response

In terms of dissociation and association, what do we look in terms of drugs? 

Low value of dissociation, high value of association

What is the dissocation constant? Symbol? Formula?

Kd; Kd = k-1/k1 (rate of drug receptor dissociation divided by association