drug response and tolerance

Special terms

Hyperreactivity

• Hyperreactivity describes unusually low dose produce the expected pharmacological reponse

Hypersensitivity

• Hypersenstivity is usually used to describe allergic reactions

Hyporeactive

• Hyporeactive describes situation where an exceptionally large dose is required to produced the desired/expected pharamcologic effect

Tolerance

• Tolerance is when hyporeactivity is acquired from chronic exposure to a drug

Tachyphylaxis

• Tachyphylaxis is where tolerance develops within a few doses of a drug
• e.g. nitrate, suxamethonium, ephedrine

Idiosyncrasy

• ... where unusual effect of a drug occurs in a small percentage of population (regardless of the dose of drug administered)

Mechanism of tolerance

1. Development of cellular tolerance

aka neuronal adaptation

• Most important of all mechanisms
• Responsible for tolerance to:
  * opoids
  * barbituates
  * alcohol

2. Enzyme induction

3. Depletion of neurotransmitter

• ... where there has been sustained stimulation

4. Formation of antibodies to the drug

• Immunity is involved