Routes of Administration - parenterals Flashcards
Describe intravenous (IV) route (1)
- Typically via a surface vein.
- From 1ml ‘injection’ up to several litres for ‘infusion’.
- IV injection rapidly increases plasma drug concentration.
- Provide 100% drug absorption.
- Infusion (drug is diluted in an infusion bag) provides a slow and controlled drug release.
What does parenteral administration mean?
- Drug administration other than via the GI tract e.g. skin
Describe intravenous (IV) route (2)
- Water-in-oil emulsions or suspensions cannot be
administered via IV as oil phrase or suspended drugs
can block blood vessels. - Hypertonic or extreme pH drug solutions can cause
inflammation and pain at injection site.
Describe subcutaneous injections.
- Also called hypodermic injections.
- Inject into the loose connective and adipose
tissues immediately below the dermal skin layer. - Typically in the abdomen, upper arms/legs.
- Highly vascular site, so absorption is rapid and
predictable. - Aqueous solutions or suspensions can be administered.
- Volumes up to 1 ml.
- E.g. insulin.
Describe intra-arterial and intracardiac injections.
- Intra-arterial is like IV administration except it is via
artery.
– More invasive and less accessible than via the veins.
– Only used when IV access cannot be established e.g.
pre-mature babies. - Intracardiac route is used only in life-threatening
emergencies to produce a rapid, local effect in the
heart.
Describe intradermal injections
- Inject into the skin between the epidermis and dermis.
- Limited to volumes of up to 0.2ml.
- Absorption is slow.
– Little interstitial fluid to facilitate drug diffusion at injection
site.
– Not well-perfused by blood. - Used for immunological diagnostic
tests and vaccinations. E.g. BCG.
Describe intramuscular injections.
- Inject into the tissue of a relaxed muscle in buttock,
thigh and shoulder. - Aqueous or oily solutions or suspensions can be
administered. - Absorption is slower than SC.
- Volume up to 4 ml.
Describe intraspinal injections - intrathecal
– This is given directly into the cerebrospinal fluid (CSF) in
the subarachnoid space or spinal canal.
– Allow drugs to bypass the blood brain barrier.
– 100% drug absorption into the CSF.
– E.g. anticancer drugs (methotrexate), antibiotics for
meningitis, analgesic.
– Volumes up to 10ml
Describe intraspinal injections - epidural
This is giiven into the epidural space between the dura mater and the vertebrae.
– E.g. spinal anaesthesia, long acting steroid.
* All intraspinal injections must be isotonic aqueous solutions
and cannot include preservatives
Describe intra-articular injections.
- Given into the synovial fluid of joints cavities.
- Suitable for aqueous solutions and suspensions.
- For anti-inflammatory drugs to treat arthritic conditions
or sports injuries. - 100% drug absorption at site of action.
Describe intraocular injections.
- Administration of drug into the eyes and sub-classified
into:
– Intracameral injections - Into the anterior chamber (in front of the lens).
- From 0.1ml to 1ml volumes.
- For antibiotics, local anaesthetics during eye surgery.
– Intravitreal - Into the vitreous chamber.
- To treat various ocular diseases (e.g. endophthalmitis).
- Max. vol. 0.1ml – minimise risk of rising intraocular
pressure and damage retina.
What are the advantages of parental routes?
- Most routes allow rapid onset of action.
- Avoids first pass hepatic metabolism thus improves
bioavailability. - Allows higher concentration of drug in the systemic
circulations or local site. - Suitable for unconscious patients, or unable to administer orally.
- Delayed onset of action is possible through intramuscular injection.
- Infusion of drugs for prolonged period is possible to maintain steady-state plasma level.
What are the disadvantages of parenteral routes?
- Usually requires healthcare professional to administer.
- Potential risks during administration e.g. air embolism, haemolysis.
- Needle-stick injuries.
- Needle phobia and poor patient acceptability.
- Formulation and manufacturing costs are higher requiring sterile and highly controlled pyrogen-free
environment. - Shelf-life is usually shorter than oral forms.
- Often requires refrigerated storage (extra cost).
Why are excipients added?
– Adjust isotonicity to match human blood.
– Adjust the pH.
– Increase drug solubility.
– Increase drug stability.
– Increase shelf life.
What vehicles are used for injections?
- Highly purified grade of water
- Saline - commonly used as an infusion vehicle
- Solubilising agents
- Co-solvent systems e.g. ethanol, glycerol
Why are solubilising agents added?
- To aid drug dissolution
For example: - Surfactants can solubilise hydrophobic drugs like diazepam
- Oil-in-water emulsions
- alpha and gamma cyclodextrins
What are preservatives?
- Antimicrobial agents are added in multi-dose products
(e.g. vials with a rubber septum). - Some co-solvents can aid drug solubility and have
antimicrobial effect:
– Ethanol
– Glycerol
– Propylene glycol
What are the common preservatives used in parenteral products?
– Benzalkonium chloride
– Benzoic acid
– Benzyl alcohol
What are antioxidants?
- Reduce drug degradation by oxidation thus extend
product shelf-life.
Give an example of an antioxidant and how it is used.
- Nitrogen gas is bubbled through the drug solutions to
displace oxygen in the formulation.
– Called ‘sparging’. - Fill the container headspace with nitrogen.
What is the physiological pH?
7.4
