Mechanism of Drug Actions



Classifications of drug actions, according to


  1. Excitatory – To stimulate function in case inhibited by disease
  2. Inhibitory – In case of hyperactivity of system/organ due to disease


Location of effect

  1. Topical
    1. Places of application
    2. All drug produces topical action
    3. Example: local anaesthetics, ointments, creams, pastes – for inflammation, allergic reactions etc
  2. General/Systemic
    1. After absorption of drug, for system effect, drug produces actions on all body cell
    2. Depends on structure of the drug – the ability of drug to cross biological membranes
    3. Types
      1. Peripheral actions
        1. By drugs that cannot cross the blood-brain barrier
        2. Hydrophilic drug
        3. Cannot dissolve into brain
      1. Central actions
        1. Produces cross-action across biological barrier, enters the CNS
      1. Reflex actions
        1. Acts on reflex pathways, causes change in body function
        2. Acts on receptor of reflex arc
        3. Example: nicotine


  1. Direct
    1. Acts on the target directly
    2. Example : oxytoxin (directly to uterine muscle), cardiatonic (directly to cardiac muscle)
  1. Indirect
    1. Action on different organ is produced by stimulation of another organ
    2. Example: caffein causes increase in urine output (caffein causes increased heart action, causes increased haemodynamic activity, causes increase in kidney activity, causes increased in urine output.)


Target II

  1. Selective
    1. Produce action only on specific organ
    2. Example: sabutamol for treating asthma : acts only to the receptor in brochioles
    3. However, in excessive dosage, it produces non-selective action in other parts
  1. Non-selective
    1. Example: epinephrine – stimulates all adrenergenic receptor ( Alpha1, Alpha2, Beta1, Beta2, Beta3)

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