Upload
meredith-oliver
View
214
Download
0
Tags:
Embed Size (px)
Citation preview
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
Con
cent
ratio
n
Time
Concentration – time
profile of an IV bolus
Con
cent
ratio
n
Time
An exponential decay
Cpt = Cp
0 x e-kt
Half-life
Con
cent
ratio
n
Time
10
5t
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
Con
cent
ratio
n
Time
MTC – Minimum Toxic Concentration
24hours
Problems with an IV
bolus
Con
cent
ratio
n
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
Con
cent
ratio
n
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
2412
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 = InfusionConcentration
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
Con
cent
ratio
n
Time
MEC
MTC
Reduced elimination
Con
cent
ratio
n
Time
MEC
MTC
Extended interval dosing with poor renal perfusion
Concentration
Time