Drug Administration

Oral
1. Advantages
  1. easy and convenient
  2. no skilled personal required
  3. prep need not be sterile
  4. immune system can cope
2. stomach
  1. pH = acidic
  2. Acid drugs
    1. mainly non-ionised
    2. readily absorbed
  3. Basic drugs
    1. mainly ionised
    2. poorly absorbed
  4. Neutral drugs
    1. readily absorbed
3. Duodenum
  1. pH = alkaline
  2. basic drugs => mainly non ionised, readily absorbed
  3. Acidic drugs => mainly ionised, absorption restricted
4. Disadvantages
  1. effects are slow
  2. absorption maybe incomplete
  3. some drugs to big to be absorbed
  4. some drugs destroyed by gut or liver
INHALATION
1. Large surface area of alveoli in lungs
2. good pulmonary blood supply
3. can have local effect on lung
4. systemic effects e.g. general anaesthetic
INJECTION
1. by-pass difficulties of absorption
2. drugs must be sterile => by passing immune system
3. exact dose is known
4. given by skilled staff
INTRAVENOUS
1. Advantages
  1. rapid effect
  2. lage volumes can be used
  3. Irritant solutions can be used
2. Disadvantages
  1. rapid delivery to heart, CNS => side effects
  2. cannot recall drug
INTRAMUSCULAR & SUB-CUTANEOUS
1. Advantages
  1. controlled onset with drug vehicle
  2. aqueous - rapid effect
  3. oily -slow effect
2. Disadvantages
  1. Damage at injection site
  2. Limited to small volumes
ROUTES determined by
1. drug chemical nature
2. how quickly an effect is required
3. how the effect needs to be maintained
4. patient condition/compliance
5. Convenience
6. many drugs bind to a plasma protein
  1. bound fraction retained in plasma
  2. unbound fraction diffuses into tissues (active)
DISTRIBUTION
1. out of plasma into tissues
2. move easily into interstitial fluid around tissues, interact with target
3. Distribution AWAY from target site => terminate effect
BLOOD-BRAIN/BLOOD-PLACENTA BARRIER
1. Capillaries in CNS = no pores
  1. only lipophilic drugs can cross capillary membrane
2. placenta good barrier
  1. only lipophilic drugs cross to foetus

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Drug Administration

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