Injections - parenteral Flashcards
What are the types of injections?
a drug is given by a route which takes it directly into body fluids, thus by-passing the preliminary process of passage across GI membranes
- directly into systemic circulation
What is an injection?
Intravenous = most common
Intramuscular
Intradermal (subcutaneous)
Intra-arterial
Intracardiac
CNS injections (intraspinal, intra-ventricular, etc.)Intra-articular
Ophtalmic injections (subconjunctival, intra-vitreal, etc.)
Where are the following injections inserted into? intradermal subcutaneous intravenous intramuscular
intradermal - into the dermis = skin layer under the epidermis (upper skin layer) subcutaneous - into the subcutaneous tissue = tissue layer between the skin and muscle intravenous = most common - into a vein intramuscular - into a muscle
What happens during an iv injection?
it is a bolus injection
- injected all at once
- concentration peaks very quickly = reaches maximum
- decreases = excretion, metabolism, distribution
What is the drip between a drip and repeated injections?
both are used for sustained release of drugs
drip
- given at a steady rate over time
- concentration increases until it plateaus in the desired level
repeated injections
- repeatedly injected when concentration levels fall below the specific therapeutic window
What are the employed types of iv formulations? What formulations should not be used?
employed types
- aqueous solutions
- oil in water emulsions
must not be used
- water in oil emulsions = not compatible with blood (70% water)
- suspensions = drugs are not fully dissolved and can clog/block the veins
What are the advantages of iv injections?
quick onset of action
- useful for when fast therapeutic responses are required
first pass metabolism is by-passed
- avoids liver metabolism
bioavailability
- 1 = entire available dose is administered and used
patient cooperation is unnecessary
- useful for unconscious patients, patient adherence is not a factor
allows precise dosing at a controllable rate
- can maintain the drug in a therapeutic level
What are the disadvantages of iv injections?
self administration is less likely so trained staff is required
drug is irretrievable
- in the case of an overdose, it cannot be retrieved
possibility of an overdose
injection site reaction
compliance
- low
sterility
What is the therapeutic window?
concentration range in which drug levels have the best effects
- must be sustained in this level
too high = toxicity
too low = ineffective treatment
What is the ideal treatment for persistent pain? When should iv and im injections be used?
breakthrough medication which can be used along side around the clock (regular) medication is ideal
- can cover the spikes of painful events that break through the regular drug treatment
iv injections are best for break throughs in pain
- fast onset of action
im injections are best for chronic pain/painful events over prolonged time
What are factors affecting the rate of drug absorption from the muscle?
blood supply to the muscle massage - can increase blood supply ionisation of drug type of formulation
What are the types of formulation for im injections?
aqueous solutions
suspensions in aqueous vehicle
suspensions in oily vehicle
- take time for drugs to diffuse through the muscle into the blood therefore the drugs will not clot blood vessels
Where are drugs inserted into? What are their properties?
site of injection is a critical factor in determining the absorption rate since different muscles have different degrees of vascularity
arm - deltoid
- most rapid absorption due to greatest vascularity
thigh - vastus lateralis
- second most rapid absorption
buttocks - gluteus maximus
- least rapid absorption
- lowest vascularity = poor circulation
What can facilitate absorption and spreading of drugs in im injections?
heat or massage can increase blood supply
addition of the enzyme hyaluronidase to the preparation facilitates the spreading of the drug in the muscle
- alters permeability of the connective tissue through the hydrolysis of the hyaluronic acid
What are the features of im injections?
allows delivery of exact amounts of drug whilst allowing site control over the rate of absorption
compared to iv
- it has slower onset, slower excretion leading to prolonged time in the bloodstream
What are the features of subcutaneous injections?
subcutaneous tissue is less vascularised than muscle tissue
- drugs are absorbed more slowly and the effects are prolonged
route is only suitable for small dose volumes
more painful than intramuscular due to greater number of nerves
high potency drugs are often given by this route due to the low amounts required (e.g. steroids)
What are the routes of administration for subcutaneous injections?
drug injected into alveolar connective tissue just below skin surface
- absorption slower than I.M. route generally
- spreads action across several hours to avoid too intense / short / frequent use
What are the different vehicle formulations? What are their properties?
water
- high chemical purity
- pyrogens free = free of substances that cause fevers
- can only be prepared by distillation
sterilised water
- used to dissolve or dilute parenterals before use
- pyrogen free
How can water be purified?
distillation of potable water
suitable pre-treatment required
- chemical softening and filtration
- deionization and pH adjustment
- followed by reverse osmosis and distillation
What are non-aqueous solvents? When are they used? What is their role?
water miscible co-solvents
- glycerin, propylene glycol (PEG)
- used in small-volume injectables
- for use via IM route
increase solubility in water
stabilize drugs degraded by hydrolysis
What are the different types of additives? What is their purpose? What are their properties?
anti-microbial agents
- excipients used to prevent the growth of bacteria
- are used in multiple dose vials = to prevent contamination as multiple doses are taken
- stable and effective in the free form at low concentrations
- may interact with other components (including packaging –rubber cap)
anti-oxidants
- prevent degradation of the active ingredient
- have a lower oxidation potential than the active ingredient = oxidised preferentially
- butylated hydroxy toluene
chelators
- remove traces of metals
= metals catalyse oxidative degradation
buffers
- ideal pH of parenteral products is 7.4
