Prescribing by other routes Flashcards
Route dependent on…? (6)
- Bioavailability (or for local effects)
- Desired peak-trough levels
- Continuous / long-term release
- Availability of routes (and tolerability)
- Contraindications
- Risks (and benefits)
Bioavailability of IV
100%
How does vancomycin exert its effect?
By having concentrations constantly maintained above
the minimum inhibitory concentration (time-dependent
killing), so better with regular, smaller doses.
How does gentamicin exert its effect?
Aminoglycosides (such as gentamicin) require peak
concentrations (concentration-dependent killing), but
low therapeutic index, so better with increased dosing
interval.
Infusions - if high concentration / low volume, should be delivered by…?
Syringe pump
Sometimes infusions require significant dilution. Give an example.
E.g. if amiodarone is given peripherally
A 18-year old man with epilepsy is currently an inpatient due to worsening control of his generalised tonic-clonic seizures.
PMH Epilepsy
DH Sodium valproate 500 mg orally 8-hrly.
He weighs 70kg.
While on the ward, he is having ongoing tonic-clonic seizures for the last 5 minutes.
He already has intravenous access sited prior to his seizure.
A Phenytoin 1.4g slow intravenous injection B Lorazepam 4mg intravenously C Diazepam 10mg intramuscularly D Diazepam 10mg rectally E Midazolam 10mg bucally
B Lorazepam 4mg intravenously
A 34-year old woman is brought to Accident and Emergency with reduced consciousness. Her partner informs you then she has been injecting heroin.
PMH Intravenous drug use - mixed substances.
DH None.
She weighs 50kg.
Following initial treatment by the ambulance services with naloxone 400 micrograms intravenously, she has improved (initial GCS 6/15). She has managed to remove her nasopharyngeal airway.
She still has intravenous access.
Examination
RR 12, Sats 96% on 28% O2 by venturi mask. Airway selfmaintained.
BP 126/68, pulse 68 regular.
GCS 14/15, no lateralising signs
There are concerns that she is about to abscond from the hospital.
A Diazepam 2.5mg orally B Lorazepam 1mg intravenously C Naloxone 400 micrograms intramuscularly D Naloxone 400 micrograms intravenously E Naloxone 400 micrograms subcutaneously
C Naloxone 400 micrograms intramuscularly
A depot intramuscularly may be helpful to prevent her opiate toxicity to return once the intravenous naloxone wears off – particularly if she has left the hospital
environment.
Subcutaneous naloxone can also be an alternative to intravenous delivery when there is no intravenous access.
A 83-year old woman is brought to Accident and Emergency, found by her carers in the morning (8AM), in bed, with weakness in her right face, arm and leg. She was well last night (10PM).
PMH Dementia, osteoarthritis.
DH. Paracetamol 1g as required (maximum 6-hrly).
SH. Lives in residential home, carers three time a
day, mobilises less than 20 yards with roller frame.
Examination
Dense right sided weakness. Unsafe swallow.
Due to the timing of her stroke, she is not a candidate for thrombolysis. She does not have a nasogastric tube in place as due to her resistance, it was not safely sited.
A Aspirin 300mg intramuscularly B Aspirin 300mg intravenously C Aspirin 300mg orally D Aspirin 300mg rectally E Aspirin 300mg subcutaneously
D Aspirin 300mg rectally
Subcutaneous infusion - commonly used in…?
Low or high volume?
Give some examples.
Low-volume (e.g. 48ml/24hr)
Commonly used in palliative care
E.g. hyocine butylbromide / hydrobromide,
midazolam, metoclopramide…
Subcutaneous pellets - what does this allow? Give an example.
Allows slow-release
E.g. oestradiol
Subcutaneous insulin formulations - human insulin are ______ at low concentrations. Aggregates into stable dimers at… (3). Forms hexamers…
monomers
higher concentrations
lower pH (2-8)
in presence of protamine
in presence of Zn2+ ions
Insulin analogues -give some examples.
E.g. Lyspro and Aspart; Glargine
What temp must long-term supplies of insulin be kept at?
Long-term supplies must be kept at 2-8C (or chemically
destabilised)
Intramuscular - small volumes.
Entry into systemic circulation - fast/slow?
Dependent on…?
Fast entry
Blood flow dependent
What are some IM injections formulated with?
Some formulated with hyaluronidase (breaking down
extracellular matrix to increase rate of diffusion)
IM injections are contraindicated in…?
Haemophilia
Intrathecal - give examples.
- Single dose analgesia
- Only very limited chemotherapy agents
- Baclofen for spasticity
- (Very rarely antibiotics)
Why is intrathecal dangerous?
Potential for respiratory depression
Benefits of epidural. (4)
- Can be larger volume than intrathecal
- Can place indwelling catheter for “top up”
- Onset ~30 minutes (~5 minutes for spinal)
- Less neuromuscular block
Complications of epidural. (5)
- Dural headache
- Bloody tap (and very rarely catheter placed in vein)
- High block
- Very rarely placed in subarachnoid space
- Epidural abcess / haematoma
Inhaled - benefits.
- Local effects
- Allows increased local concentration in lungs (lowering systemic side effects)
- Ease of delivery, rapid exchange and titratability
Inhaled - still systemically absorbed, so some are modified to reduce systemic absorption e.g.?
Ipratropium
Intranasal examples.
Most commonly DDAVP (desmopressin)
Possible route for sedation with midazolam (used abroad, not yet licenced in UK)
PR is either for … or ….
Either for local effects (e.g. antiinflammatory
in ulcerative colitis) or systemic delivery
Benefits of PR.
Useful when unable to take medications (e.g.
vomiting / severe nausea / NBM) and when difficult to establish intravenous access (e.g. status epilepticus)
Disadvantages of PR.
- often unreliable
* difficult to predict
When is buccal/sublingual used?
- Note fentanyl lozenges
* Also when drug is unstable at gastric pH or rapidly metabolised by liver e.g. GTN
NG tubes if displaced results in …?
aspiration risk
PEG/PEJ tubes risk
localised infection
Topical - what for? Most have ___ lipid solubility (so…?).
Typically for local effects (e.g steroid creams)
Most have low lipid solubility (so systemic absorption for
there are low, unless broken skin or excessive dosing)
What topical substances are well absorbed?
Some toxic substances (e.g. organophosphates)
Topical can also be for systemic delivery. What is the benefit of this?
Steady rate of delivery
“Smoother” plasma concentration profile
Examples of systemic delivery topical.
These are usually lipid soluble/insoluble.
E.g. GTN, hyocine, opiate analgesia, oestrogens, nicotine
SOLUBLE
Endotracheal medications - WHEN ARE THESE USEFUL?
Useful in cardiopulmonary arrest if tracheal intubation successful but IV access not available
When are intraosseous medications used?
In cardiopulmonary arrest, or occasionally paediatric
resuscitation
Complications of intraosseous medications.
Complications include embolism, compartments syndrome, fractures, infection/osteomyelitis
