IV Injection Lectures Flashcards
What’s the difference between an IV bolus and an IV infusion?
An IV bolus is injected very quickly whereas an IV infusion is administered much slower
What are the advantages and disadvantages of an IV bolus injection?
Gets a high concentration of the drug very fast
Useful for emergency treatments as a result
However must monitor for toxicity and irritation
What ADME processes are NOT associated with IV injections? Why?
Absorption and the first pass effect. This is because the drug doesn’t need to be absorbed since it directly enters systemic circulation. Because of this there is also no first pass effect, drug is distributed into the tissues before passing the liver.
What is the disposition of a drug? Why is this considered in IV injections?
A given drug’s elimination and distribution characteristics
Describe the plasma profile of an IV bolus. What are the two phases?
Initial distribution phase where concentration of drug rapidly falls due to the distributing out of the plasma.
Elimination phase where equilibrium is determined. Slow decline due to elimination of the drug from the body.
When the distribution phase is very short what model do we use?
The one-compartment model
Why is the one compartment model suitable for drugs with very short distribution phases?
Only the elimination phase is observed thus we can assume the body is acting as a single compartment.
What is the first order elimination equation for the one-compartment model (in amount of drug and in concentration)?
C = C0*e^-kt
A = A0*e^-kt
What are the assumptions of the one-compartment model?
Volume of the compartment equals volume of distribution.
Elimination is first order
Elimination follows linear kinetics
How can we determine k graphically?
By calculating the gradient
How would you apply the 1st order elimination equation to any two points in time?
Substitute variables x and x0 for x2 and x1
How can you determine the kinetics of a drug from semilog paper? Why can’t you calculate k from semilog paper?
If zero order, horizontal line
If first order, straight diagonal line
If second order, curved line
Can’t calculate k from semilog paper due to the logged axis, too hard to identify the gradient accurately. Excess calculations required.
What equation links clearance to the elimination constant?
Cl = V*k OR k = Cl/V
What is the elimination half life?
The amount of time for half of the drug to be eliminated
How can we use successive half lives to “predict” a drug concentration at a given time?
By calculating the number of half lives that would pass to reach a given time, we therefore know how many times the original concentration must be halved to estimate the concentration at a given time.
What is the equation for AUC?
AUCinf = C0/k
What equation relates AUC to clearance?
AUCinf = D/Cl
Why is AUC the preferred method to. estimate clearance?
It is model independent and thus always correct regardless of the PKs of a drug.
Elimination half life equation? How do you derive it?
t1/2 = 0.693/k
If you can’t remember it, derive it from the regular ln equation
What are the advantages and disadvantages of IV infusion?
Drug plasma levels can be easily controlled, constant drug plasma levels can be achieved whilst suffering less problems due to irritation or toxicity from the drug.
However,
It requires continuous monitoring, requires drugs to be quite soluble and stable and can’t be used on fluid restricted patients.
What must be considered with an IV infusion that isn’t with an IV bolus?
An input rate must be considered with an IV infusion.
One compartment IV infusion equation?
C = (R/Cl)(1-e^-kt)
What are the three phases of IV infusion?
Accumulation phase
Plateau/steady state phase
Post-infusion phase
Why is the steady state IV infusion equation so simple?
Since over long periods of time (1-e^-kt) equates to 1 and thus can be removed.
