Pharmacology : Drug Administration

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  • Created by: Sophie
  • Created on: 16-01-13 12:42
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  • Drug Administration
    • Delivery
      • Drugs are available in diff. forms
        • Determined  by:
          • Chemical/ biological stability
            • Route of admin
              • Convenience
                • Formulation
                  • Determined  by:
                    • Chemical/ biological stability
                      • Route of admin
                        • Convenience
                          • Formulation
        • Main routes of admin
          • Inhalation
            • Sublingual
              • Oral
                • Application to epithelial surfaces
                  • Rectal
                    • Injection
                      • Main routes of admin
                        • Inhalation
                          • Sublingual
                            • Oral
                              • Application to epithelial surfaces
                                • Rectal
                                  • Injection
        • Routes involving GI tract
          • Sublingual
            • Drug must not have unpleasant taste
              • Under the tongue
                • Only for small MW drugs
                  • Rapid absorption from mouth to systemic circulation
                    • This way avoids:
                      • pH of stomach
                      • passage through liver in portal circulation
            • This way avoids:
              • pH of stomach
              • passage through liver in portal circulation
          • Oral (aka per oralis)
            • Most common route
          • Bioavailability
            • Defined as proportion of admin. dose that is delivered to systemic circulation
              • Ionisation of drug affects absorption
                • Most drugs are weak acids or weak bases
                • pH in gut affects ionisation
                • Absorbed drug lost to metabolism by enzymes in gut and liver
                  • Bioavailability
                    • Defined as proportion of admin. dose that is delivered to systemic circulation
                      • Ionisation of drug affects absorption
                        • Most drugs are weak acids or weak bases
                        • pH in gut affects ionisation
                        • Absorbed drug lost to metabolism by enzymes in gut and liver
            • Rectal
              • Drug delivered as; suppository (wax base), enema (liquid)
              • For local inflammation
              • For systemic effects
          • Routes involving epithelial surfaces: topical for local
            • Most drugs are weakly absorbed across skin
              • Nasal mucosa- nasal sprays
                • Cornea- eye drops
            • Topical for systemic
              • Some drugs cross skin due to high-lipid solubility
                • Delivered as; liquids, ointments, transdermal patches
          • Injection
            • Intravenous
              • Fastest route to systemic
                • Drug delivered as sterile liquids
                  • Used for:
                    • Seriously ill, unstable drugs, drugs poorly absorbed
            • Subcutaneous
              • Injection under skin
                • Faster than oral, slower than IV
                  • Rate depends on:
                    • Drug diffusion and removal by local bl. flow
            • Intramuscular
              • Into muscle
                • Similar to SC but slower
            • Intradermal
              • Into skin
                • Breaks dermis layers
                  • Local effect; Not used for systemic effect
                    • Very slow release
              • Intracerebro-ventricular
                • Into ventricles of brain
                  • For drugs that can't pass through blood-brain barrier
                    • eg.antiobiotics
                • Epidural (Intrathecal)
                  • Into a subarachnoid space by lumbar puncture
                    • For drugs that can't pass blood-brain barrier
                      • For local admin.
          • Inhalation
            • Delivery to lungs in inspired air
              • Systemic effects
                • Gases
                  • Gas molecules dissolve in lung fluids
                    • Diffuse into bl. in pulm. circulation
                      • Rapid exchange between bl. and gas phase
                • Local effects
                  • Inhalation
                    • Delivery to lungs in inspired air
                      • Systemic effects
                        • Gases
                          • Gas molecules dissolve in lung fluids
                            • Diffuse into bl. in pulm. circulation
                              • Rapid exchange between bl. and gas phase
                        • Local effects
                          • Delivered as liquid droplets/ fine powders
                            • Importance of particle size:
                              • >10 microns - hit throat + swallowed
                              • <10 - enter lungs
                              • <1 micron - enter lungs but cross into bl. for systemic effects
                  • Delivered as liquid droplets/ fine powders
                    • Importance of particle size:
                      • >10 microns - hit throat + swallowed
                      • <10 - enter lungs
                      • <1 micron - enter lungs but cross into bl. for systemic effects
          • Dose
            • Amount of drug administered
              • Taken as single dose or bolus
                • concentration = amount/volume
                  • Drug conc.determines effect
                  • Body volume
                    • Dose expressed relative to body weight (mg/kg)
                    • Dose should vary with body size
                    • Placebo effect
                      • Can be as high as 50% in some diseases
                      • Some people are helped by taking a 'medicine' in some diseases, even if a tablet of chalk

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