11. Prescribing with Different Drug Routes Flashcards
An 18yo man with epilepsy is currently an inpatient due to worsening control of his generalised tonic-clonic seizures. PMH: epilepsy. DH: sodium valporate 500mg 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 IV access sited prior to his seizure. What is the most appropriate management option?
a) Phenytoin 1.4g slow IV injection
b) Lorazepam 4mg IV
c) Diazepam 10mg intramuscularly
d) Diazepam 10mg rectally
e) Midazolam 10mg bucally
b) IV delivery would be most appropriate in this emergency, when the route is available.
C, D and E: with presence of IV route, this would not be optimal. A: appropriate if the benzodiazepine was unsucessful in terminating the seizure, since A is slower acting than B
A 34yo woman is brought to A&E with reduced consciousness. Her partner informs you she has been injecting heroin. PMH: IV drug use - mixed substances. DH: none. She weighs 50kg. Following initial treatment by the ambulance services with naloxone 400mg IV, she has improved (initial GCS 6/15). She has managed to remove her nasopharyngeal airway. She still has IV access.
Examination
RR 12, Stats 96% on 28% O2 by venturi mask, airway self-maintained. BP 126/68, pulse 68 regular. GCS 14/15, no lateralising signs.
There are concerns she is about to abscond from the hospital. Select the most appropriate management option at this stage.
a) Diazepam 2.5mg orally
b) Lorazepam 1mg IV
c) Naloxone 400 micrograms intramuscularly
d) Naloxone 400 micrograms IV
e) Naloxone 400 micrograms subcutaneously
c) depot intramuscularly may be helpful to prevent her opiate toxicity to return once the IV naloxone wears off, esp. if she has left the hospital. Subcutaneous naloxone can also be an alternative to IV when no IV access.
A, B: she already has reduced consciousness and it would be unsafe to give her sedation regardless of route. D: her GCS is >13/15 so no immediate need to quickly reverse opiate toxicity via IV. E: can be alturnative to IV when there is no IV access. Not indicated in this setting
An 83yo woman is brought to A&E, 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 6hrly). SH: lives in residential home, carers 3 times a day, mobilises <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 doesn’t have a nasogastric tube in place as due to her resistance, it was not safely sited.
Select the most appropriate management option at this stage:
A) Aspirin 300mg intramuscularly
B) Aspirin 300mg IV
C) Aspirin 300mg orally
D) Aspirin 300mg rectally
E) Aspirin 300mg subcutaneously
d) appropriate route
A, B. E: Aspirin unavailable as an IV, intramuscular or subcutaneous preparation. C: pt does not have a safe swallow and the absence of a working NG tube - at risk of aspiration.
What is pharmacokinetics concerned with?
How should vancomycin and aminoglycosides e.g. gent be administed via IV injection?
For an IV infusion, how should a high concentration/low volume drug be adminstered?
Absorption (route, drug, formulation e.g IV tend to peak at 5-10m, oral 30m-1hr), distribution, metabolism, excretion.
Vancomycin: conc constantly maintained above minimum inhibitory conc (time-dependant killing), so regular, smaller doses. Aminoglycosides: require peak concs (conc-dependant killing), but low theraputic index, so increase dosing interval
By syringe pump, sometimes require significant dilution (e.g amiodarone given peripherally b/c it’s toxic to veins)
How can subcutaneous drugs be administered?
Describe intramuscular drug administration.
Infusion (low volume, common in palliative care), pellets (allow slow release e.g. oestradiol), insulin formulations (human insulin monomers at low conc b/c high concs aggregate, insulin analogues e.g glargine). Site, depth and massaging influences absorption.
Small volumes, fast entry into systemic circulation (blood flow dependant, useful if no IV access), can de depo preparations for slow absorption e.g. progesterones. Contraindicated in haemophilia -> MASSIVE TRAUMA
What is intrathecal drug administration?
How does epidural differ from intrathecal?
Single dose analgesia, inject into spinal canal/sub arachnoid space so it reaches CSF, only very limited chemo agents, Baclofen for spasticity, potential for respiratory depression.
Can be larger volume, into epidural space of SC, can place indwelling catheter for ‘top up’, onset about 30mins (5mins for spinal), less neuromuscular block - more analgesic effects. Problems: headache, bloody tap, high block, haematoma
Describe drug administration via inhalation.
Describe intranasal drug administration.
Describe PR drug administration. When might it be used?
Local effects by e.g. nebuliser allows local concentration in lungs (decreasing systemic SEs, but still systemically absorbed e.g. salbutamol -> bradycardia). Also systemic effects e.g. gaseous anasthetics.
Nasal mucosa highly vascularised. Local effects e.g. anti-congestants, and sytemic e.g. DDAVP. Not often used
Local (e.g. anti-inflammatory in ulcerative colitis) or systemic delivery. Systemic absorption often unreliable and hard to predict. Useful if can’t take medications orally and hard to establish IV access (e.g. status epilepticus)
Describe PV drug administration.
Describe buccal/sublingual drug administration.
Describe NG/PEG/PEJ drug administration. (Percutaneous endoscopy gastrostomy/Percutaneous endoscopic jejunostomy)
Long term, continuous e.g. hormonal IUD, mainly local effects
Buccal = cheek, sublingual = under tongue. Oral mucosa, absorption can be very quick. Useful if drug unsable at gastric pH or rapidly metabolised by liver e.g. GTN.
Similar to oral meds. NG tubes usually shorter term, if displayed = aspiration risk. PEG/PEJ tubes usually longer term, can sometimes cause localised infection. Be wary of volumes of water required to administer crushed drugs
Describe topical drug adminstration.
What are two forms of emergency access?
Typically for local effects e.g. analgesia or steroid cream, most have low lipid solubility thus low systemic absorption. Can be for systemic delivery: steady rate e.g. GTN, opiate analgesia, oestrogens, nicotine, usually lipid soluble.
1. Endotracheal medications: useful in MI if tracheal intubation successful but IV unavailable, requires higher dose than IV.
2. Intraosseous medications: in MI or paed resus, in long bones, medullary cavity contains venous sinusoid network. Typically tibia/femur. Complications = embolism, compartment syndrom, fracture, infection
