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

MODES OF DRUG ACTION

Pharmacodynamics - what the drug does to the body?

Principles of drug action

Drugs do not impart new functions – except gene therapies

Basic types of drug actions are:

• Stimulation - enhancement of existing level of action
  • Eg. adrenaline on heart, pilocarpine on salivary gland
• Depression - selective diminution of activity of specialized cells
  • Eg. barbiturates on CNS, Acetylcholine on heart
• Irritation - a nonselective, often noxious stimuli. Mild irritation on some cells (skin, connective tissue) stimulate some functions for a beneficial effect.
  • Eg. Bitters, topical counterirritants but severe irritation inflammation, necrosis, damage
• Replacement - of natural substances eg.. hormonal therapy, deficiencies
• Cytotoxicity - eg.  Antibacterials, antivirals, anticancer agents

Mechanisms of drug action

• Physical action – physical property of the drug causes the main action
• Eg. mass of the drug - bulk laxatives
• Adsorption -- charcoal
• Osmosis -- mannitol
• Radioactivity – ¹³¹I - for hyperthyroidism
• Radioopacity – as contrast media (barum)
• Chemical action – chemical property of the drug responsible for action
• Antacids - AlOH_{2 ­}
• acidifiers, - NH₄Cl
• alkalinizers, - NaHCO₃
• oxidizers -- KmnO₄, H₂O₂
• chelating agents – Ca Na EDTA, BAL, Pencillamine