Dv: Define Tachyphylaxis, Tolerance, Addiction, Dependence & Idiosyncrasy


  • A decreased response to a drug which develops over minutes-hrs
  • ­↑dose will not ­↑response
  • Usually due to 2nd msg depletion or receptor internalisation
  • ie depletion of stored NA on repeated Ephedrine doses


  • larger doses are required to produce the same pharmacological effect
  • Occurs over days-weeks


  • continued compulsive use of drug despite adverse health or social consequences.  Addiction is a neurobiological disease with genetic, psychosocial and environmental factors.  Individual uses a drug (drug abuse) → not all these people will go on to have addiction.  Characterised by behaviours: impaired control of drug use, compulsive use, continued use despite harm, craving
  • Ie         Few patients who use opioids for post op pain will desire drug on withdrawal


  • repetitive exposure to a drug → body adaption → when drug is no longer available → signs of withdrawal à this is known as Dependence
  • Ie withdrawal of nitrate VDs → rebound HTN → physical dependence


  • rare & unpredictable response, not dose related.  Caused by genetic differences in drug metabolism or immunologic mechanisms
  • ie         G6PdH deficiency → hemolysis with oxidative stress (ingestion of Fava beans)