Continuous Infusion (Cut off for Exam 2) Flashcards
Continuous Infusion Advantages
- Convenient in critically ill patients
- Rate of infusion is regulated
- Avoid fluctuating peak and trough blood levels associated with multiple dosing
- Electrolysis and nutrients may be given along with IV medications
- Duration of therapy is easily controlled
Drug Concentration in Plasma
X = Ro/K * (1 - e^(-Kt))
C = Ro/VK * (1-e^(-Kt))
Ro = Infusion Rate
Drug Infusion
- Concentration builds up exponentially
- Hits an asymptomatic or plateau rate (Css)
- Css = steady state level
Steady-State Drug Concentration
-Determined by setting time to infinity, rate is equal to rate out
Rate in = Ro
Rate out = Cl = VK
When is steady state reached?
Css = Ro/VK
- Only infusion rate and clearance control this rate (not time)
- 4-7.5 half lives (4 for this class)
Desired Css
Ro = Css * VK
Post-Infusion
- t = T and C = Ct when infusion is stopped
- Ct = Ro/VK * (1-e^(-Kt))
- Decline in drug concentration after stopping infusion is described by same equation for IV bolus injection
- C = Ct * e^(-Kt’)
- t’ = time elapsed after stopping infusion
- Ct = concentration when infusion stopped
Reaching Css
C = Css * e^(-Kt’)
After infusion has stopped
Apparent Volume of Distribution
At Css: Css = Ro/VK ==> V = Ro/CssK
Drug Infusion: V = Ro/CK * (1-e^(-Kt))
Clearance
Cl = VK = Ro/Css
Fraction Css Reached
fss = 1 - e^(-0.693N)
N = ln(1 - fss)/-0.693
fss = fraction of Css achieved at various times
N = t / half life time
Loading Dose
-Given to obtain desired steady-state concentration as rapidly as possible
DL = V * Css OR DL = Ro/K
CLD = Dose/V * e^(-Kt)
-Following simultaneous IV bolus injection and infusion to stead state, drug concentration is as follows:
CLD + CINF = Dose/V * e^(-Kt) + Ro/VK * (1 - e^(-Kt))
What determines the approach to steady-state?
Half life
If a drug is given at a higher infusion rate, will steady state be reached more rapidly?
No
