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Infusions

Infusions. Mark Tomlin Consultant Pharmacist: Critical Care Southampton University Hospitals NHS Trust. Characteristics of IV therapy. Half-Life ? What Dose ? Intermittent Infusion ? How Often ? With Loading Dose ? Continuous Infusion ? Effect of organ dysfunction ?.

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Infusions

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  1. Infusions Mark Tomlin Consultant Pharmacist: Critical Care Southampton University Hospitals NHS Trust

  2. Characteristics of IV therapy • Half-Life ? • What Dose ? • Intermittent Infusion ? • How Often ? • With Loading Dose ? • Continuous Infusion ? • Effect of organ dysfunction ?

  3. Concentration – time profile of an IV bolus Concentration Time

  4. Concentration – time profile of an IV bolus An exponential decay Concentration Cpt = Cp0 x e-kt Time

  5. Half-life Described by a constant decay factor or: Concentration t 10 5 t Time

  6. Half-life - t • Defined as the time taken for the concentration, of a drug, in the blood, to halve. • We usually dose at the half-life • If the half-life is less than 4 hours then the medicine is usually administered by infusion. • After 5 half-lives, the drug is completely eliminated so it describes the duration in the blood • Prescribe mg/kg/hr or μg/kg/min to remind staff about response delays after dose adjustments

  7. Characteristics of IV therapy • Half-Life ? • What Dose ? • Intermittent Infusion ? • How Often ? • With Loading Dose ? • Continuous Infusion ? • Effect of organ dysfunction ?

  8. Problems with an IV bolus Concentration MTC – Minimum Toxic Concentration Time 24hours

  9. Problems with an IV bolus MEC – Minimum Effective Concentration Concentration Time 24hours

  10. Characteristics of IV therapy • Half-Life ? • What Dose ? • Intermittent Infusion ? • How Often ? • With Loading Dose ? • Continuous Infusion ? • Effect of organ dysfunction ?

  11. An Intermittent Infusion End Infusion MTC – Minimum Toxic Concentration Concentration MEC – Minimum Effective Concentration Time 24hours

  12. Characteristics of IV therapy • Half-Life ? • What Dose ? • Intermittent Infusion ? • How Often ? • With Loading Dose ? • Continuous Infusion ? • Effect of organ dysfunction ?

  13. How often ? – Intermittent bolus MTC MEC 24 12

  14. How often ? – adjacent bolus MTC MEC 12 24

  15. How often ?- accumulating bolus MTC MEC 12 24

  16. Characteristics of IV therapy • Half-Life ? • What Dose ? • Intermittent Infusion ? • How Often ? • With Loading Dose ? • Continuous Infusion ? • Effect of organ dysfunction ?

  17. Accumulating bolus – with Loading Dose or not? MTC LD Concentration MEC How long? Time

  18. Characteristics of IV therapy • Half-Life ? • What Dose ? • Intermittent Infusion ? • How Often ? • With Loading Dose ? • Continuous Infusion ? • Effect of organ dysfunction ?

  19. Short Half-life ? MTC Concentration MEC 10 mins Time

  20. Short Half-life = Infusion MTC Concentration MEC 10 mins Time

  21. Characteristics of IV therapy • Half-Life ? • What Dose ? • Intermittent Infusion ? • How Often ? • With Loading Dose ? • Continuous Infusion ? • Effect of organ dysfunction ?

  22. Reduced elimination MTC Concentration MEC Time

  23. Reduced elimination MTC Concentration MEC Time

  24. Extended interval dosing with poor renal perfusion Concentration Time

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