VPT 311: General and Systemic Veterinary Pharmacology (2+1)

FEATURES OF DOSE RESPONSE CURVE

Plotting of dose response curve

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