iv infusions
TRANSCRIPT
1Intravenous infusion
INTRAVENOUS INFUSION
BAZLA SIDDIQUI
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INTRAVENOUS INFUSION
"Drug administration through the intravenous route at a constant rate over a determined time interval.“
Intravenous: administering a solution into or within a vein
Infusion: slow injection of a substance into a vein or subcutaneous tissue
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Cont…
IV solutions may be given either as :
a bolus dose
or infused slowly through a vein into the plasma at a constant or zero order
rate.
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PURPOSE OF IV INFUSIONMaintenance of stable plasma concentration.
Avoidance of periods of low drug concentrations.
Maintenance of clinical effectiveness.
Dosage adjustments
Maintain or replace body store .
Restore acid base balance
Administer medication
Provide Nutrition6Intravenous infusion
ADVANTAGES OF IV INFUSION
An immediate therapeutic effect is
achieved due to a rapid delivery of the drug/fluid
to target sites
Pain and irritation caused by some
substances when given intra
muscularly or subcutaneously is
reduced.
if patient cannot tolerate drug by
oral route, iv route is
applicable.
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ONE COMPARTMENT MODEL DRUGSIV INFUSION
• This can be obtained by high degree of precision by infusing drugs i.v. via a drip or pump in hospitals
• The body is considered as a single, kinetically homogeneous unit.
• This model applies only to those drugs that distributes rapidly throughout the body.
• -Drugs move dynamically in an out of this compartment
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PLATEAU LEVEL OR STEADY-STATEONE COMPARTMENT MODEL
DRUGS•At steady state, the rate of drug leaving the
body is equal to the rate of drug (infusion rate) entering the body.
Rate of drug input= rate of drug output
• the rate of change in the plasma drug concentration
dC p/dt = 0
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PLATEAU LEVEL OR STEADY-STATE
Drug accumulates in the body during an infusion as a function of the difference b/w drug in and drug out
In one compartment model, Infused drug follows:
•Zero order input
•First order output
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Cont…
Css can be determined by the equation:
Css= ko/Cl or R/Cl
ko = Rate of constant intravenous infusion (mg/h)
R = infusion rate
Cl = Clearance
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Example
• 1. An antibiotic has a volume of distribution of 10 L and k =0.2 hr-1. A steady-state plasma concentration of 10 g/mLis desired. The infusion rate needed to maintain this concentration can be determined as follows.
• Equation
Css= R/Cl
Cl= VD.k
R=CssVD.k
R=(10)(10)(1000)(0.2)
R=20mg/h
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Example 2:A patient was given an antibiotic (t 1/2 = 6 hr) by constant IV infusion at a rate of 2 mg/hr. At the end of 2 days, the serum drug concentration was 10mg/L. Calculate the total body clearance Cl T for this antibiotic. Solution:
Equation used is:Css= R/Cl
So Cl=R/Css
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LOADING DOSE PLUS IV INFUSION:
THE LOADING DOSE:
• Css achieved immediately
• obtain desired concentrations
IV INFUSION:
• loading dose is sustained by infusion rate.
Superimposition of two contributing processes to the plasma concentration at any time would produce a sustained plasma concentration.
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LOADING DOSE PLUS IV INFUSION:
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INCREASING THE INFUSION RATE :
If a drug is given at a more rapid infusion
rate, a higher SS drug concentration is obtained but the time to reach SS is
the same.
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LOADING DOSE PLUS IV INFUSION:Cp LEVEL:
• If loading dose in body at time t is
e-kt
• Then steady state achieved by infusion is
1-e-kt
• Plasma concentration at steady state is
Cp= Css-(1-e-kt)
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CP LEVEL
Plasma concentrations during the start of an infusion and after the infusion has been switched off once a steady state has been achieved.
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EFFECT OF LOADING DOSES
In practice the solution is to give an
iv bolus loading dose at the start of
the infusion equal to the required therapeutic
concentration
Reason: time delay b/w start of infusion and attainment of pleateu level may not be desirable.
Sustained plasma concentration can
be achieved by exactly matching
the infusion rate to replace the drug loss
by elimination of loading dose.
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DRUG PLASMA CONCENTRATION
• Total concentration at any time is:
• Sum of contributions made by loading dose and the infusion rate
• Equation for calculating plasma concentration at any time (Cpt) is:
• Contribution from loading dose + contribution from infusion
• Cpt= D/V .e-kt + ko/Cl.(1-e-kt)
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CALCULATION OF ELIMINATION HALF LIFE OF DRUG
It is defined as time taken for the amount of drug in the body as well as plasma concentration to decline by ½ or 50% its initial value.
Css versus time relationship may be used to calculate k or indirectly elimination half life of drug in patient.
One or more plasma samples must be taken at a known time after infusion.
It is expressed in hrs or mins
t1/2 = 0.693/k 23Intravenous infusion
Cont…
•Half life is secondary parameter that depends upon the primary parameters clearance and volume of distribution
•Knowing the half life in the general population helps to determine if the sample is taken at steady state in the patient.
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CLINICAL APPLICATION OF CONTINUOUS IV INFUSION:
• For drugs with a narrow therapeutic window, IV infusion maintains an effective constant plasma drug concentration by eliminating wide fluctuations between the peak (maximum) and trough (minimum) plasma drug concentration.
• Prevent toxicity that might occur if the drug is presented too quickly
• E.g:
• Immune reactions
• Hypotensive reaction
• Local damage to vein25Intravenous infusion
EXAMPLES OF CLINICAL APPLICATION
Insulin in hyperglycemic
coma
Heparin in acute
thrombosis
Liginocaine in acute
arrythmias
Isosorbide for vasodilation
Adrenergic agonists
Diazepam for antiepileptic
control
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ANALOGUES OF THE INFUSION MODEL IN DRUG DELIVERY
Transdermaldrug delivery
depot implants/ injections
Oral controlled
release dose forms
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EXTRAVASCULAR ADMINISTRATION
• Extravascular route:
• Oral, intramuscular, rectal, buccal.etc.
• Dosage form first has to release the drug which then has to be absorbed from the site of administration.
• For systemically acting drugs, absorbtion is prerequisite for therapeutic activity
• Bioavailabilty and absorbtion rate constant need to be considered.
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INTRAVENOUS INFUSION OF TWO COMPARTMENT MODEL DRUGS
• Many drugs given by iv infusion follow two compartment kinetics
Example:
The drugs follow two compartment models are:
• Theophylline
• Lidocaine
Iv infusion requires a distribution and equilibration of the drug before a stable blood level is reached.
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Cont…
• This compartment helps to explain distribution within the body which is not 'instantaneous', that is slow enough to see in the plasma concentration versus time curve.
• This shows up as a rapid drop at first with elimination and distribution, followed by a slower phase.
• During a constant infusion , drug in the tissue compartment is in distribution equilibrium with the plasma
• Constant Css level result in constant drug concentration in the tissue
• No net change in amount of drug in tissue occurs during steady state.
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SUMMARY
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THANKYOU
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