23 pharmacology of CNS and breathing Flashcards
What are analeptics?
respiratory stimulants
What type of drug is Doxapram, and why is it so widely used?
it’s an analeptic
came around in the 50’s and we simply don’t have anything better
How long does it take for Doxapram to take effect, and what is its’ half life like?
effective in under a minute, it has a short half life , which is problematic
What is the mechanism of Doxapram, what is a problem with this?
stimulates CO2 and O2 chemoreceptors to fire more AP’s
It non-specifically enhances electrical activity in the respiratory centre
so it can therefore effect many other hings
What are 2 adverse effects of Doxapram?
cardiac arrhythmia
convulsion
When is Doxapram used?
clinical emergencies
acute ventilatory failure with hypercapnia (COPD)
maybe with post-op depression
mechanically - assissted respiration preferred
What is the general principle of respiratory depressants?
any agent with a generalised CNS depression will do this
the neurones in the respiratory centres aren’t special, so we have a lot of potential drugs
How does respiratory function respond to respiratory depressants?
What is the clinical significance of this?
it resists it tbh, which is interesting
we therefore normally give people GA’s
What are the 2 main types of GA’s?
volatile anaesthetics like haloethane
injected ones
What is the physiologcial action of volatile GA’s?
decreased response of CO2 chemoreceptors
partial pressure of arterial CO2 will rise
name 2 benxodiazepines
Diazepam (Valium)
Temazepam
Why might people be given benzodiazepines before a GA?
to relieve anxiety (also used to manage epilepsy too)
What is the physiological action of benzodiazepines?
decrease hypoxic drive, at higher doses we see an effect on central chemoreceptor action, although this is still not fatal
How might GABA inhibit neurone activity?
When GABA binds to an ion channel, it opens it to allow Cl- in, inhibiting depolarisation
Benzodiazepine has an allosreric effect, allowing more Cl- in
name 2 barbituates
phenobarbital or thiopental
What is the physiological action of barbituates?
decreased response of central chemoreceptors
decreased hypoxic drive
What is the mechanism of action of barbituates?
increased inhibitory neurotransmission via GABA(A) receptors
What problems are associated with barbituaes?
they work on their own without GABA so can be fatal
the dose at which they produce an anaesthetic effect is very close to the fatal dose
they’re just abused
What is the mechanism of action of alcohols?
increased GABA(A) inhibitory transmission decreased NMDA excitatory transmission inhibits release of neurotransmitter by inhibiting VGC Ca2+ channels
What is the physiological effect of alcohols?
decreased response to CO2
Name 3 types of opioids
Morphine
Fentanyl
Heroin
Which opioid receptors are targeted for analgesia?
mu
What problem arises with opioid tolerance?
people come off it (great!) which decreases their tolerance again, but then they might go back to the same high doses, which can be fatal
What is the ideal situation with opioids?
achieving analgesia without respiratory depression
What is the mechanism of action of opioids?
What is the physiologcial effect?
Opens K+ channels with GCPR’s
this hyperpolarises the membrane, decreasing excitability
CO2 receptor response decrease
Name 1 opioid receptor antagonist
When is it used?
Naloxone
to quickly treat an overdose
What will the effect be of mixing benzodiazepines, opioids, and alcohol?
death
What will be the effect of using benzodiazepines with a GA or opioid?
assissted ventilation use
Name a benzodiazepine antagonist and its’ use
flumazenil
useful for benzodiazepine or alcohol overdoses
although if their respiratory function is good enough we would just wait until they’ve metabolised the benzodiazepine
