Barbiturates

Question 1

barbs in bottle vs body

Answer 1

alkaline in bottle

acidic in body

Question 2

barbs preparation, pH, storage, potent isomer

Answer 2

sodium salt preparation
highly alkaline, bacteriostatic in bottle
stable/sterile for 6 days
levo isomer is potent

Question 3

barbs are derived from:

Answer 3

urea + malonic acid = barbituric acid

Question 4

barbs substitutions

Answer 4

carbon 2 & 5 substitutions have sedative, hypnotic properties

Question 5

barbs branched chain @ 5

Answer 5

increased hypnotic activity

Question 6

barbs phenyl group @ 5

Answer 6

increased anticonvulsant activity

Question 7

barbs methyl radical group

Answer 7

increased convulsants (methohexital)

Question 8

barb sulfuration

Answer 8

fat soluble, short duration, rapid onset, increased potency

Question 9

barb chain length and potency

Answer 9

long branched chain is more potent than straight

Question 10

barb isomer comparisons

Answer 10

levo is 2x more potent than dextro isomer

Question 11

barb mixture availability

Answer 11

only available as racemic mixture

Question 12

barb w/ oxygen @ #2 name

Answer 12

oxybarbiturate

Question 13

barb with sulfur @ #2 name

Answer 13

thiobarbiturate

Question 14

barbiturate relative potency

Answer 14

thiopental = 1
thiamylal (surital) = 1.1
methohexital (brevital) = 2.5

Question 15

barb mechanism of action

Answer 15

enhance GABAa activity
decrease transmission of sympathetic ganglia = hypotension
mimics GABA at receptor
decreases post synapse membrane sensitivity to aCh - some muscle relaxation, not surgical depth
depresses reticular activating system = sleep

Question 16

barbs pharmacokinetics

Answer 16

rapid onset
rapid redistribution - will wake up in 5-7 minutes
extensive metabolism
70-85% protein bound
blood fat partition = 11
pK = 7.6

Question 17

barb metabolism

Answer 17

oxybarbiturates = hepatic only
thiobarbiturates = hepatic and extra hepatic
side chain oxydation at carbon 5 to carboxylic acid
desulfuration, hydrolysis opens ring
renal excretion
heavy hepatic enzyme inducers!

Question 18

Barb elimination T1/2

Answer 18

thiopental - 11.6 hrs
prolonged in pregnancy due to increased protein binding
methohexital - 3.9 hrs

Question 19

barb CNS effects on LOC

Answer 19

decrease LOC, CMRO2, CBF, ICP

can produce isoelectric eeg

Question 20

barb CNS excitatory effects

Answer 20

paradoxical excitement

methohexital - myoclonus and hiccups

Question 21

barb CNS protection

Answer 21

very good cerebral protection

Question 22

barb SSEP monitoring

Answer 22

barbs do not affect sensory output from spinal cord

Question 23

barb and pain threshold

Answer 23

small doses can cause anti-analgesia

Question 24

barb skeletal muscle relaxation/IOP

Answer 24

no skeletal muscle relaxation

decreased IOP

Question 25

barb CV effects

Answer 25

decrease SNS, so decrease PVR, preload decrease SBP, increase HR minimal myocardial depression

Question 26

barb and trauma

Answer 26

DO NOT GIVE if SNS is not intact, hypovolemic, will see significant decrease in BP and contractility histamine release with rapid IV push, further decreases SBP minimal effect with PO barbs

Question 27

barb resp effects

Answer 27

dose dependent depression of medullary and pontine ventilatory centers (CNS) decreased ventilatory response to hypoxia, hypercarbia apnea incomplete depression of laryngeal and cough reflex

Question 28

stage 2 of induction**

Answer 28

excitatory stage with laryngospasm, bronchospasm when dose is not large enough

Question 29

Which barb has most potent hepatic enzyme inducer

Answer 29

phenobarbital

Question 30

barb increases metabolism of what?

Answer 30

``` oral anticoagulants phenytoin TCAs corticosteroids Vit k ```

Question 31

barb and heme

Answer 31

accelerates production of heme by stimulation of D aminolevulinic acid synthetase

Question 32

barbs and thrombosis, placenta

Answer 32

increases venous thrombosis | readily crosses placenta

Question 33

barbs and pts with siezures

Answer 33

metabolize drug 2x faster, (especially muscle relaxants)

Question 34

barbs and tolerance

Answer 34

enhances own metabolism, increases tolerance

Question 35

barb allergies

Answer 35

1:30,000, high anaphylaxis mortality

Question 36

barb dosing

Answer 36

Thiopental 3-5 mg/kg IV, decrease with age/pregancy, increase with infant, peds Methohexital 1-2 mg/kg IV; 20-30 mg/kg peds duration of single IV induction: 5-8 minutes due to rapid redistribution

Question 37

what not to mix with barbs

Answer 37

``` opioids, catechols, NMBs, midazolam pancuronium vecuronium atracurium alfentanil sufentanil midazolam LR (too acidic) ```

Question 38

barbs and arterial injection

Answer 38

``` immediate vasoconstriction, pain dilute w/ NS phenoxybenzamine heparin brachial plexus block papaverine 40-80mg in 10-20ml NS or 5-10ml lido ```

Question 39

barbs and prophyria

Answer 39

DO NOT GIVE BARBS TO PATIENTS WITH PROPHYRIA