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 ?

Concentration – time profile of an IV bolus Concentration Time

Concentration – time profile of an IV bolus Concentration Time An exponential decay C p t = C p 0 x e -kt

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

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

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

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

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

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

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

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

How often ? – Intermittent bolus MEC MTC 24 12

How often ? – adjacent bolus MEC MTC 2412

How often ?- accumulating bolus MTC MEC 2412

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

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

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

Short Half-life ? Concentration Time MTC MEC 10 mins

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

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

Reduced elimination Concentration Time MEC MTC

Reduced elimination Concentration Time MEC MTC

Extended interval dosing with poor renal perfusion Concentration Time