Intravenous Infusions of Admixtures
Intravenous infusion of many sterile drug products requires admixture preparation. Admixture is prepared by addition of measured amount of one or more drugs or additives to a large volume parenteral fluid. The additive can be transferred to a large volume parenteral in the pharmacy (Fig C), or at patient’s bedside by injecting the additive into an intravenous port. Antibiotics, electrolytes, vitamins and trace minerals are examples of some additives used in intravenous admixtures.
Figure C- Transfer of a medication into an IV bag
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Solved Problem: A patient is receiving an infusion from a 500 ml bag containing 0.5 % of drug Z. The drop factor is calibrated at 12 gtt/ml and the flow rate is set to 10 gtt/min. If the infusion is to run for 4 hours, how much of the active drug in mg will the patient receive? Approach Use the following equations to calculate the volume of infusion $$ Volume \ of \ infusion = { Infusion \ rate \times time } $$ Equation 1 In addition we know that, $$ Drip \ rate = Drop \ factor \times Infusion \ Rate $$ Rearranging, equation 2, to get infusion rate: $$ Infusion \ Rate = {Drip \ rate \ ( 10 { gtt \over min } ) \over \ Drop \ factor \ ( 12 { gtt \over ml}) } $$ Equation 2 Plug in equation 3 in equation 1 $$ Volume \ of \ infusion = {10 \ gtt \over min } { \times } { ml \over 12 \ gtt} { \times} {60 \ min \over hr} {\times } {4 \ hr} $$ Equation 3 $$ Volume \ of \ infusion \ = \ 200 \ ml $$ We know that 0.5 g is present in 100 ml, use ratio and proportion calculate the amount of drug in 200 ml, $$ {0.5 \ g \over 100 \ ml } = {x \ g \over 200 \ ml} = 1 \ g $$ Answer: 1000 mg |
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Solved Problem: An IV infusion for a patient weighing 185- lb calls for 10 mg/kg of amikacin to be added to 1000 ml of 5 % dextrose for injection. How many milliliters of an amikacin injection containing 500 mg/ 2 ml should be used in preparing the infusion? Approach -1: set up a dimensional analysis to calculate ml of amikacin required. Convert pounds to kg. $$ x \ ml = {10 \ mg \over kg } {\times} { kg \over 2.2 \ lb } { \times } { 132 \ lb } { \times } {2 \ ml \over 500 \ mg } $$ $$ x = 2.4 \ ml $$ Approach -2: set up a dimensional analysis to calculate ml of amikacin required. Convert pounds to kg. $$Patient's \ weight = {132 \over 2.2 \ lb } = {60 \ kg}$$ $$ Patient's \ dose = {60 \times 10 } = {600 \ mg } $$ $$ {500 \ mg \over 2 \ ml} = {600 \ mg \over x \ ml} $$ $$ x = 2.4 \ ml $$ Answer: 2.4 ml |