IV drug administration Flashcards
Learning outcomes
To explain the indications/contraindications for, the advantages/disadvantages of, and the risks associated with intravenous drug therapy.
To identify the types of intravascular devices (including delivery devices and drivers) that may be used to deliver drugs and fluids.
To interpret the effects of varying basic pharmacokinetic parameters (e.g. clearance) upon the plasma concentration of IV drugs following bolus, continuous or intermittent infusions.
What are the reasons IV administration may be used
Medicine is not available in another form
Cannot tolerate medication by another route
Constant or high blood level of medicine is needed
A rapid onset of effect is needed
Some medications are more effective via IV (bioavailability?)
Rarely, to ensure compliance
What are the disadvantages of IV administration?
Increased cost and time to administer the medicine Requires trained staff to administer (plus location)
Rapid onset of action
Volume of fluid needed to dilute the medicine
Can cause discomfort/pain to the patient
Health risks (e.g. infection)
When oral route can be used, it should
What are the types of intravascular devices (IVDs)?
Peripheral venous catheters
Central venous catheters (CVCs)
– Peripherally inserted CVCs
– Skin-tunneled CVCs (e.g. Hickman and Broviac lines)
Arterial catheters
What are the different methods of administering IV medications and their uses?
Continuous infusion – Stable drugs – Short half-life – Time dependent effects – Needs dedicated IV site
Bolus injection
– Rapid response required
– Incompatibilities (Drug - solution(?))
– Unstable drugs
Intermittent infusion – Unstable drugs – Long half-life – Concentration dependent effects – Less compatibility concerns
What are some complications of IV drug administration?
Fear / Phobia / Pain Infection / Sepsis Thrombophlebitis Extravasation / Infiltration Emboli Anaphylaxis / Hypersensitivity Overdose Insufficient mixing
Stability of medicines in solution – Light (e.g. total parenteral nutrition [TPN]) – Temperature (e.g. insulin, TPN) – Concentration (e.g. amiodarone) – pH (e.g. midazolam)
Interaction of medicines with the syringe/bag
What signs should be looked for in guarding against signs of phlebitis
Pain at insertion site
Redness(erythema) at insertion site
Swelling at the infection site
Pain along path of cannula
Describe Red Man syndrome
Hypersensitivity reaction due to histamine release
– erythematous rash of face, neck, and upper torso
– diffuse burning, itching, generalised discomfort
– rare cases: hypotension, angioedema, chest pain, dyspnea
Commonly caused by Vancomycin
– Treatment of MRSA
Incidence reduced by
– Slowing infusion rate
– More dilute drug solution
What should be considered when prescribing vancomycin
Body weight (Affects loading dose, vol of NaCl 0.9% or glucose 5%, and duration of infusion)
What is the bioavailability in IV administration?
Fraction of unchanged drug that reaches the systemic circulation.
IV injection gives 100% bioavailability.
Discuss plasma drug concentrations
IF drug is infused at a constant rate AND no drug is removed from the body, then the graph of plasma concentration against time would be a straight line.
BUT drug is being eliminated from the body as soon as it is in the circulation (e.g. via the kidneys).
For most drugs, the amount of drug eliminated per unit time is related to the concentration of drug in the plasma (first-order kinetics):
– Higher concentrations, more drug is removed per unit of time. – Lower concentrations, less drug is removed per unit of time.
THEREFORE the graph of plasma concentration against time for most infusions will bend towards a plateau when the rate in of drug equals the rate out.
Discuss plasma drug concentration during IV infusion
Plasma concentration increases during infusion until rate of input equals rate of output
• “Steady state” (Css)
What is clearance in IV drug administration
Clearance (CL) is defined as the volume of blood or plasma cleared of drug in a unit time – e.g. 10ml/min
In first order kinetics, whilst amount of drug eliminated per unit time varies, CL is a constant
How do you calculate the plasma steady state concentration (Css)
The Css value reached depends on:
the rate of drug administered (K0)
OVER
volume of plasma cleared of drug per unit time (CL)
The time taken to reach Css depends on:
elimination half-life (t1/2)
t1/2 directly depends on the volume of distribution (Vd) and
inversely on the clearance (CL) of drug from the body:
t1/2 =
ln2xVd
OVER
CL
Where In2 = natural log of 2 (0.693)
Vd = dose/plasma conc.
What is the clinical impact of clearance?
What contributes to CL? (MD3002!)
What happens if your patient’s CL is lower or
higher than expected?
– To the steady state plasma concentration?
– To the time taken to reach that steady state?
What happens if you increase or decrease the dose of a drug?
– To the steady state plasma concentration?
– To the time taken to reach that steady state?
