Dose response curve in pharmacology

Dose response curve

As the name indicates this refers to the plotting of the dose vs response, with the dose in X axis and response in some measurable units in the Y axis. The features of the curve so obtained will provide useful information about the action of the drug or in comparison among drugs.

Features of dose response curve

1. Effect- Y axis and Dose – X axis – hyperbola
2. Effect- Y axis and Log Dose – X axis – sigmoid curve
3. By taking log dose – a linear relationship in 30 – 70 % range gives a possibility of prediction of response in this range
4. Response is proportional to an exponential function of the dose
5. Log dose response curves are used to
   • display wide range of dose – effect
   • compare agonists and antagonists
6. Potency – amount of drug required to elicit a response
7. Relative potency – more meaningful than absolute potency
   • Eg. Drug A (potency 10mg) more potent than drug B (100 mg)
8. A 10 times more potent than B – rightward shift of DR curve if less potent
9. Potency need not mean clinical superiority
10. Efficacy – the maximal effect produced by a drug and refers to the peak obtained in the DR curve.
11. Eg. Morphine produces very high analgesia that cannot be obtained with any dose of aspirin 
12. Morphine highly efficacious than aspirin

Quantal dose response curve

1. Quantal DR curve due to biological variation ( diff. among individuals in response to same treatment) the response to drug dose in a population occurs as a frequency distribution.
2. A cumulative freq. Distribution (as % of individuals showing effect plotted against log dose —> yields the quantal DR curve
3. The dose that produces desired effect in 50% – ED₅₀
4. The dose that produces death in 50% – LD₅₀
5. Therapeutic index = LD₅₀ / ED₅₀