Barbiturates Flashcards
2 barbiturates:
1.
2.
- THIOPENTAL
- methohexital (brevital)
pH: thiopental
10.5
this is the reason that thiopental burns on injection; not because of an additive, but because it is so basic
also the reason that thiopental is bacteriostatic; to basic to support bacterial life
why did Europe stop selling US thiopental
we were using it for lethal injections
problem with injecting thiopental after fentanyl
fentanyl pH: 4
thiopental pH: 10.5
precipitate would form in veins as a result of two drugs mixing
stability of thiopental:
supplied in what form?
anhydrous
stability of thiopental after reconstitution:
- anhydrous
- refrigerated
- room temp
- indefinitely
- 7d
- 24hr
mechanism of action: thiopental
GABA
1.
2.
- decreased dissociation of GABA from receptors; increased inhibitory side of CNS, decrease excitatory side
- direct action/opening of chloride channel
mechanism of action: thiopental
sympathetic nervous system
decreased transmission: pseudosympathectomy
decreased BP
increased HR
(just like propofol)
pharmacology of barbiturates
1.
2.
3.
4.
- highly lipid soluble; onset of 30sec
- highly protein bound
- quick uptake because of high lipid solubility
- high redistribution: absorbed into fat as soon as it left brain -> hangover
thiopental: IV induction dose
3-5mg/kg
thiopental onset/duration
onset: 30-40sec
peak: 1min
duration: 5-8min
thiopental: protein binding
80%
thiopental: metabolism
- where
- length of time
- active metabolites
- thiopental v. methohexital
- metabolized in liver; liver dysfunction can further increase duration of action (decreased blood flow, hepatic function)
- slow metabolism
- no active metabolites
- Thiopental for inpatient procedures; methohexital for outpatient procedures
thiopental: elimination
renal elimination. no metabolites, so not a concern for pts with kidney diseases
thiopental: clinical uses
1.
2.
3.
- induction of anesthesia once-upon-a-time (Europe will no longer sell to US)
- treatment for increased ICP
- cerebral protection
thiopental was used as an induction agent from ________ to ________
1934 to 1989 (introduction of propofol)
55yrs
two types of ischemia
focal ischemia (only ischemia to one part of the brain, collateral flow perfuses brain everywhere else)
global ischemia (heart stopped, no flow anywhere)
value: normal cerebral perfusion pressure
80-100mmHg