glasgow royal infirmary pharmacy department pharmaceutical aspects of intravenous drug...
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Glasgow Royal InfirmaryPharmacy Department
PHARMACEUTICAL ASPECTS OF
INTRAVENOUS DRUG ADMINISTRATION
Differences IV ORAL route
IV administration leads to: Higher peak
concentrations Greater total quantity of
drug absorbed Avoids 1st pass
metabolism However requires more
training, knowledge, skills and precautions
time
Conc.
IV route - Advantages
Emergency situations / immediate response e.g. adrenaline in cardiac arrest.
Loading dose e.g.digoxin, phenytoin Patient unable to swallow or tolerate
other routes Sustained drug levels required Drug cannot be given by another route
because of its chemical property e.g. cytotoxics, cefotaxime
Less painful than I.M. injection. Administration can be stopped
quickly Allows dosing of unconscious,
uncooperative and uncontrollable patients.
To achieve effects unattainable by oral administration.
IV route - Disadvantages
Risk of toxicity Risk of embolism Risk of extravasation/phlebitis Fluid overload Problems with compatibility + stability Risk of microbial contamination Increased cost More training required
BOLUS 3-10 minutes
Quick/easy/economical Tendency to administer too quickly
causing damage to veins. Sudden anaphylactic reactions Only limited volumes can be
administered
Intermittent IV INFUSION 20-120 minutes
One-off or repeated doses E.g. Gentamicin, vancomycin,
erythromycin High plasma concentration
achieved rapidly over longer periods.
Continuous IV INFUSION
Delivers constant level of drug Used for drugs with a rapid elimination
rate or a very short half-life e.g. midazolam
BUT Fluid overload, incompatibility,
contamination, incomplete mixing, phlebitis and rate calculations can be problematic.
Formulation of I.V. drugs
Reconstitution required-Dry powder e.g. amoxicillin-Allows prolonged storage
BUT- Is time consuming- Risk of contamination, foaming, glass particles, pressurised vials.
Solutions needing further dilution
e.g. Ranitidine, Amiodarone No reconstitution necessaryBUT Time consuming Prone to vacuum/pressure problems Can cause glass breakage Risk of microbial contamination.
‘Ready to use’
No further dilution needed Come in bags/small volume amps/syringes e.g.
metoclopramide, adenosine, morphine PCAs Easy to use & time saving Minimal microbial contaminationBUT Microbial contamination Fluid overload
Factors influencing Stability & compatibility
A proportion of the drug will be lost between time of preparation and
entry into the bloodstream by degradation, precipitation or an
interaction.
Degradation
By hydrolysis in aqueous solution May be accelerated by pH change Minimised by using reccomended
diluent
Photodegradation Breakdown by light. e.g. Vitamin A,
sodium nitroprusside, liposomal amphotericin.
May not be clinically important provided direct exposure to strong daylight is avoided e.g. furosemide.
Precipitation Precipitates are inactive but harmful:
can block catheters, damage capillaries and cause emboli.
May be transparent or pale Affected by differences in pH Anions and cations mix to form ion
pairs Most drugs are more soluble as temp.
increases
Blinding of drugs to plastics
Most equipment made from plastic
Drug binding difficult to predict as it depends on:
Conc. Flow rate, vehicle, surface area, temp. pH and time.
Care with insulin, diazepam, nitrates....
Leaching of plasticisers Oils and surfactants contained in
PVC bags can leak out and affect compatibility and stability of drugs.
e.g. Ciclosporin infusion must be used within 6 hours as polyethoxylated castor oil in the solution causes phthalate to leach from PVC.
Summary
Add one drug at a time following manufacturers advice
Mix thoroughly to avoid layering Examine solution regularly Add most concentrated or most soluble
additive first Strongly coloured solutions will hide
reactions Observe patient for ADR’s
Intravenous AntibioticsState for each of the following:
Diluent & volume required for reconstitution
Volume required for doseType of injection
Gentamicin 260mg Erythromycin 750mgCo-amoxiclav 1.2g Metronidazole 500mg
Tazocin 4.5g
Example (1) How would you prepare and administer
Flucloxacillin 1g IV?
Each 1g vial should be reconstituted with 20ml WFI (SPC)Add 20ml reconstituted solution to 100ml NaCl 0.9% or glucose 5% (BNF)Can be given as an infusion over 30-60min. or bolus injection over 3-4 min. (BNF & SPC)
Example (2) How would you prepare & administer
Vancomycin 1250mg
Each 500mg vial should be reconstituted with 10ml WFI – Use 3 vials (BNF Appendix 6)Got 1500mg 30ml
1250mg 1250 x 30 / 1500 = 25mlConc. of infusion fluid must be ≤ 5mg/ml (BNF)Therefore put 25ml into 250ml of Nacl 0.9% or Glucose 5%Must be given as an infusion (SPC & BNF)
References to use BNF appendix 6 BNF monographs SPC (www.emc.medicines.org.uk) Technical leaflet JHO handbook Medusa I.V. drugs guidance manual (
www.medusa.wales.nhs.uk) Ward clinical pharmacist Medicines information (ext 24407)
How would you prepare and administer:
Gentamicin 260mgCo-amoxiclav 1.2gTazocin 4.5g Erythromycin 750mgMetronidazole 500mg
Answers Gentamicin 260mg
4 x 80mg/2ml vials. Withdraw 6.5ml and add to 100ml NaCl 0.9% or Glucose 5%. Give over 30-60 min.
Co-amoxiclav 1.2g1.2g vial reconstituted with 20ml WFI. Bolus (3-4min.) or infusion in 50-100ml NaCl0.9% given over 30-40min.
Answers (cont) Tazocin
4.5g vial reconstituted with 20ml WFI or NaCl 0.9%. Bolus (3-5min.) or infusion in 100ml NaCl 0.9% over 20-30min.
Erythromycin 750mg1000mg vial reconstituted with 20ml WFI. Withdraw 15ml (750mg) and add to 250ml NaCl 0.9%. (Cannot get 150ml bag!!) Infuse over 60min.
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