Sympathomimetics Flashcards
Sympathetic organ synapse
involves post ganglionic neuron synapsing directly at the target organ; kidneys release dopamine (vasodilation), sweat glands release ACH (thermoregulation)
two major types of sympathetics receptors
alpha and beta, different roles at different sites in the body
Mimetics also called
adrenergic agonists
lytics also called
adrenergic antagonists
Mimetics role
increase release of neurotransmitters, block reuptake into the presynaptic neuron, decrease metabolism
Lytics
decrease neurotransmitter release, deplete vesicular stores, decrease synthesis of neurotransmitters
3 types of adrenergic neurotransmitters
dopamine, epinephrine, norepinephrine; all very different, commercially available and regularly used, have to give continuously
baroreceptor reflex
when baroreceptors sense increase in BP, will try to turn off sympathetic and turn on parasympathetic with M2 receptors
Dopamine
works as an agonist on dopamine receptors, all have B activity, a vasopressor; dose dependent causes range of responses
Norepinephrine (levophed)
agonist at a1, a2, B1, very little B2, a pressor; a1=vasoconstriction and increase in BP; B1 *net effect decreases HR
Norepinephrine (levophed)
agonist at a1, a2, B1, very little B2, “best” pressor; a1=vasoconstriction and increase in BP; B1 *net effect decreases HR
longest time any pt is on Norepinephrine
12 days, try to take off drug as soon as stabilized
ADRs of norepinephrine
arrhthmies, bradycardia, peripheral ischemia, HA
Epinephrine
Most non-selective, works on all adrenergic receptors, a1=vasoconstriction, B2=vasodilation in skeletal muscle, a and B cancel out with potential for small increase in BP; B1 increases HR
Uses of epinephrine
used with local anesthesia to capitalize on vasoconstriction to keep local; anaphylaxis, bronchodilator, symptomatic bradycardia, asystole, VT
ADRs of epinephrine
chest pain, arrythmia, flushing, hypertension, tachycardia, anxiety
Phenylephrine (neo-synephrine)
a1 agonist, hypotension, no direct effects on heart; increase BP and peripheral vasoconstriction will trigger baroreceptor reflex and decrease HR; slows tachycardia
uses of Phenylephrine (neo-synephrine)
nasal decongestant, spray or red eyes, drops; also used as decongestant, sudafed; use 3 days and stop or effects will decrease
Rebound congestion
repeated topical exposure to a* agonist results in receptor desensitization, increase dose to get effects and increase again
Isoproterenol is considered a B agonist because
it requires very large doses to activate alpha receptors
Pressors should be infused via
a central line
Practical consideration of pressors
receptor site selectivity is dose dependent, limb threatening in severe case of estravasation, continuous monitoring required,often required during surgery to balance anesthesia
a2 agonists uses and medication
used for HTN and muscle spasticity; clonidine (catapres), Methlydopa (aldomet), Tizanidine (zananex), guantacine (tanex)
a2 agonists uses and medication
used for HTN and muscle spasticity; clonidine (catapres), Methlydopa (aldomet), Tizanidine (zananex), guantacine (tanex)
