Modified drug release

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  • Created by: Labake
  • Created on: 27-03-17 16:45
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  • Modified Drug release
    • For oral dosage
    • Limitations to dosing
      • Conc of drug in plasma fluctuates after dosage even after steady state
      • Forgotten or overnight doses for drugs with short half lives e.g. biological drugs
    • Advantages
      • Peaks & troughs minimised – steady state therapeutic levels to better manage disease
        • Improved Compliance- less frequency doses
          • Better safety margin- Lower side effects
            • Efficient use of drug – lower overall amount used
              • Reduction in healthcare costs- less monitoring, shorter treatment time, less dispensing (single dose).
    • Disadvantages
      • Risk of dose dumping (lethal dose)
      • Instability of drug, more costly manufacturing process
    • Drug delivery systems
      • Sustained Action:
        • An initial release of drug sufficient to provide a therapeutic dose soon after administration. Then a gradual release over an extended period.
      • Prolonged Release:
        • Drug  absorbed over longer period of time. Onset  delayed due to slower release rate from the dosage form.
      • Extended Release (ER):
        • Releases drug slowly. Plasma conc maintained for long time (usually between 8 and 12 hours)
      • Repeat  Action:
        • 1 dose  released soon after admin. Second or third doses are released at later intervals
          • First priming  doe is rapid
          • Layered tablet or tablet within a tablet
      • Controlled Release (CR):
        • Release drug at a constant rate and provide plasma concentrations that remain invariant with time.
      • Delayed Release:
        • Drug not released immediately following admin. but at a later time e.g. enteric-coated tablets.
          • For site specific absorption
    • Controlling rate of release
      • 1. Physical barrier
      • 2. Chemical barrier
      • To keep plasma conc. of drug constant
        • OR to keep it declining at VERY slow rate, plasma conc in therapeutic range for long time
      • Release rate should equal clearance rate
        • Affected by different GI pHs (2 to 8), age, race, disease and food intake
        • Use initial priming (loading) dose then add more maintenance doses
    • Drugs suitable for MR
      • Drugs with biological half life of 2-8hrs
        • Below 2 hours= cleared quickly and LARGE dose needed
          • High risk of dose dumping
        • Above 8hrs= no need for MR as lasts long already
      • Drugs with large theraperutic window
      • Log P between 2.2- 3.3
      • Permeable and uniformly absorbed in GIT
      • Moderate potency that requires small doses
        • Very potent drug= dose dumping risk
      • PHYSIO-CHEMICAL properties (solubility, stability, pKa)
        • Aim for high solubility and high permeability (Class 1)
          • Class 2 okay for controlling solubility (low solubility, high permeability)
        • Exceptions: Vancomycin- high solubility but low permeability- fine for C.diff or MRSA in gut

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