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Barbs Flashcards

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1
Q

Barbiturates

A

-prepared as sodium salts
-derived from barbituric acid
urea + Masonic acid = barbituric acid

-HIGHLY alkaline drug preparation [[bacteriostatic]]
^nature of drug is an acid

-thiopental [[TPL]] prepared at room temp is stable and sterile for 6 days

[[comes in powder and have to mix up]]

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2
Q

Barbiturate use now

A

thiopental [[pentothal]]
no longer available

methohexital
[[used for electric shock therapy]]

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3
Q

Barbiturate structure

A

substitutions at Carbon 2 & 5
[[sedative, hypnotic properties ]]

branched chain at carbon 5
[[increased hypnotic activity]]

Phenyl group at Carbon 5
[[increases anticonvulsant activity]]
^phenobarbital

methy radical imparts convulsant activity
[[some convulsant activity in brain]]
^methohexital

sulfuration –> more fat soluble, increased lipid solubility;

  • shorter DOA
  • more rapid onset
  • increased potency

LONGER chain more potent than shorter chain

Levo- isomer 2x more potent than dextro -isomer

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4
Q

Barbiturates are only available as

A

RACEMIC mixtures

oxygen at carbon 2
[[oxybarbiturate]]

sulfur at carbon 2
[[thiobarbiturate]]

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5
Q

Sulfuration

A

fat soluble; increased lipid solubility

increased lipid solubility causes;

  • short duration of action
  • more rapid onset
  • increased potency
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6
Q

Long carbon chains

A

MORE potent than short chain

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7
Q

Which isomer is more potent

A

LEVO

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8
Q

Relative Potency of Barbiturates

A

Least potent;
Thiopental [[pentothal]] –> 1

Thiamyla [[surital]] –> 1.1

Methohexital [[brevital]] –> 2.5
*most potent; dose will be lower

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9
Q

Barbiturate Mechanism of Action

A

**mimics GABA at GABA a receptor
directly activates Cl channel

-decreases the rate GABA disassociates from its receptor
[[increases duration of GABA
activity at GABA a receptor; keeping Cl channel open longer]]
^enhances GABA activity

-decreases postsynaptic membrane sensitivity to Ach
[[some muscle relaxation; but NOT enough for surgery]]

BRS explanation;
Barbiturates bind to GABAa receptor Cl Channel complex
[[different binding site than one for Benzos and for GABA]]

at low doses;
allosterically prolong GABA induced opening of Cl channel
[[enhance GABA NT effects]]

at higher doses;
mimics GABA activity
[[barbs independently open the Cl channel]]

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10
Q

Barbiturate Interaction with GABA receptor causes

A

-functional inhibition of the post synaptic neuron

-depresses RAS (reticular activating center)
[[RAS needed for consciousness; depress it = sleep/ unconscious]]

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11
Q

Barbiturate Pharmacokinetics

A

-Rapid onset of action
^Thiopental pKa; 7.6
close to 50;50
[[ionized vs nonionized]]

-Redistribution
[[rapid termination of effect]]
^Very lipid soluble
[[fat:blood partition coefficient 11]]

  • extensive metabolism
  • Thiopental; 70-85% protein bound

-

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12
Q

Barbiturate Metabolism

A

Racemic mixtures;

  • oxybarbiturates; hepatic metabolism
  • Thiobarbiturates; hepatic metabolism and additional

Oxidation occurs at Carbon 5
[[becomes carboxylic acid and terminates activity]]

Hydrolysis open ring
[[desulfurization]]

metabolized to water soluble compounds

primarily excreted by kidneys
[[<1% excreted unchanged]]

E1/2 t;
Thiopental; 11.6 hours
prolonged in pregnancy r/t increased protein binding

Methohexital; 3.9 hours

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13
Q

Which Barbiturate has a prolonged duration of action

A

Thiopental

normal E1/2 t; 11.6

prolonged in pregnant woman because of increased protein binding

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14
Q

Barbiturate CNS effects

A

-depresses LOC
[[depresses RAS]]

-cerebrovascularconstriction
decreases CBF
decreases ICP
decreases cerebral 02 requirement 
[[cardiac OR thiopental for people with hx of stroke for cerebral protection]]
^cerebral protection

Decreases intraoccqular pressure

CAN produce isoelectric EEG
[[flat line]]

Paradoxical excitement;
methohexital –> excitatory skeletal movements [[myoclonus and hiccups]]

Does NOT interfere with SSEP monitoring
[[Somato sensory evoked potential –> spinal surgery monitoring to make sure surgeon isn’t getting too close to nerves]]

small doses decrease pain threshold ‘anti-analgesuic’
[[feel pain faster–> give opioids for pain]]

no skeletal muscle relaxation

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15
Q

Barbiturate CV effects

A

-depress vasomotor center [[medulla]] and decrease SNS outflow from CNS
[[peripheral vasodilation;
decreased SVR, decreased preload]]

-SBP decreases
[[ r/t decreased SVR from dilation from depressed vasomotor center]]
HR increases to compensate in healthy normovolemic patients

-MINIMAL myocardium depression

-ORAL barbiturates produce minimal CV effects
[[anti-seizure meds are PO barbiturates]]

Rapid IV injection causes release of histamine
[[constriction]]

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16
Q

Barbiturate Respiratory effects

A

-Dose Dependent depression of medullary and pontine ventilatory centers
[[Brainstem; medulla and pons]]

-decreased ventilatory response to hypoxia and hypercarbia
[[decreased 02 and increased C02 have little effect on respiratory drive]]

-Apnea

-some depression of laryngeal and cough reflexes; but not significant t
[[people used to still cough with intubation when using]]

-

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17
Q

Rapid IV administration of Barbiturates causes

A

HISTAMINE release

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18
Q

Rapid IV administration of Barbiturates causes

A

HISTAMINE release

[[histamine casques contraction]]

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19
Q

GABA a receptors characteristics

A

Ligand gates ion channel

cyc-loop [[5; pentamer]]
[[2 alpha; 2 beta; 1 gamma]]

inhibitory

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20
Q

Too small of a dose of Barbiturates can cause

A

STAGE 2 [[excitatory phase]] like response to airway manipulation

increased risk of;
laryngospasm
bronchospasm

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21
Q

Avoid Barbiturate use in patients with …

A

PORPHYRIA

[[Disorders resulting from buildup of certain chemicals related to red blood cell proteins]]

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22
Q

Barbiturate DOSE

[[Thiopental]]

A

Thiopental

IV; 3 - 5 mg/ kg

Decease Dose;
-with age; 30% for elderly

-first trimester of pregnancy

Increase Dose in PEDI
pediatrics; 5 - 6 mg/kg

infants; 7 - 8 mg/kg

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23
Q

Barbiturate Dose

[[Methohexital]]

Study These Flashcards
A

Methohexital

IV 1 - 2 mg/kg

PR dose in Pedi; 20-30 mg/kg

24
Q

What happens when you give a Barbiturate to an acidotic patient

Study These Flashcards
A

MORE EFFECT
pKa 7.6 acidic drug

alkaline preparation but drug is ACID

if pt alkaloid less effect

25
"what are barbiturates affects on BP?"
DIRECT Acting decreases transmission in sympathetic ganglia can also mimic and enhance GABA on GABAa
26
Which drug provided 'hangover effect'
Thiopental [[pentothal]]
27
What drug is prolonged in pregnant women
Thiopental increased protein binding
28
What drug used to be given to provide cerebral protection in cardiac OR for pt going on bypass
Thiopental
29
Which drug causes excitatory skeletal muscles
Methohexital [[hiccups and clonus]]
30
[[Autonomic]] SNS is NOT intact in what situations
Extremes of age; elderly and babies hypovolemia REALLY large dose ^^these situations decrease dose to avoid severe drop inBP and myocardial depression
31
Other Effects of Barbiturates
-can cause venous thrombosis
32
Effects on Placenta
crosses placenta babies born a little more sedated
33
what will happen if patient on PO Barbiturate for seizure disorder
will RAPIDLY metabolize drugs 2-3x as fast *especially MUSCLE relaxants [[use longer acting]]
34
Nausea / vomiting incidince
INCREASED incidence with barbiturates [[compared to versed --> benzo]] BUT lower than with; etimodate ketamine inhaled anestetics *Propofol [[induction med]] best antiemetic; has some antiemetic effects
35
Tolerance to Barbiturates
develops RAPIDLY switch peoples seizures meds from one barb to another hepatic enzyme inducers of their own cells [[start metabolizing very quickly]]
36
Effects on Hepatic Enzymes
Barbiturates INDUCE hepatic enzymes tolerance develops rapidly [[not uncommon for people on PO barb seizure meds to have to switch meds bc develop tolerance]]
37
Allergies to Barbiturates
- not very common 1: 30,000 if it did occur HIGH MORTALITY usually occurred in atopic patients [[**asthma; autoimmune]]
38
Why cant we mix Barbiturates with other things
solution pH is so alkalotic (10); only mix with NS and sterile water CAN'T mix with other things, especially acids [[versed, opioids, NMB; ver, sufentanil, alfentanil]] *** it'll turn to crystals cant even mix with LR
39
Whats happens if Barbiturate accidentally gets injected ARTERIALLY?
MASSIVE vasoCONSTRICTION A LOT of pain crystalline precipitation in arterial vessel ``` [[allergic rxn in vessel]] inflammatory respsonse in vessel -vasoconstriction -microembolization [[can lose limb]] ```
40
How do you treat and accidental injection of Barbs into arteries
Phenoxybenzamine [[very long acting; alpha antagonist; covalently binding --> noncompetitive antagonist]] other tx; Dilute the effect by flossing with normal saline heparin urokinase [[prevent thrombosis]] brachial plexus or stellate ganglion block [[decrease sympathetic activity to limb]] papaverine right on vessel [[vasodilate]] 40-80mg in 10-20 ml of NS or 5-10 ml in 1% lidocaine
41
Porphyrias
group of inborn error of metabolism [[genetic disorder]] *something wrong with enzymes deficiency in enzymes in the heme production pathways results in accumulation of porphyrins [[heme]] [[because cant be converted to hemoglobin]] accumulation of porphyrins; the heme precursor is very toxic to tissues in high concentrations *any increase in heme requirement causes an accumulation of the precursor immediately before the area of the enzyme block [[ex. menstral cycle, stress, increased altitude, **anything that causes you to produce more heme 'causes an attack'
42
Most important Porphyrins in humans
heme; main precursor of hemoglobin
43
Biggest problem with Prophyria
accumulation of heme is VERY TOXIC to tissues in high concentrations
44
Other facts about Porphyria
- non sex linked, autosomal dominant, variable expression [[chromosome 11]] * genetic disorder inborn error of metabolism [[something wrong with enzymes]] attacks [[build up of heme]] more common in women in their 30s and 40s
45
Porphyrias triggered by
**most important trigger are drugs some hormones some event that increases heme concentration
46
Drugs that trigger Porphyrias
Barbiturates [[thiopental, methohexital]] Etomidate Pentazocine
47
S/S of Porphyrias
-severe ab pain with diarrhea and vomiting - ANS instability [[tachycardia, HPN]] -electrolyte disturbances [[EKG changes]] - skeletal muscle weakness - respiratory failure - seizure - neuropsych disturbances
48
When do we use Methohexital
ECT --> electric shock therapy severe depression ECT done in hospital under general anesthesia ECT[[shock given too brain]] is timed with EEG Why? it maintains EEG [[does not produce isoelectric EEG like other induction meds causes bursts [[methy radical added to benzoic acid provides some convulsant activity]]
49
Why is methohexital good for electric shock therapy
 Methyl radical imparts convulsant activity (methohexital)  some convulsant activity in brain Does not produce flat line on EEG [[no isoelectric EEG]]
50
Only barbiturate we really use
METHOHEXITAL
51
Barbiturate with substitution at Carbon 5
sedative and hypnotic prosperities
52
Barbiturate with branch chain at Carbon 5
INCREASES hypnotic activity
53
Barbiturate with Phenyl group at Carbon 5
INCREASES ANTIseizure activity | [[PHENObarbital]]
54
Barbiturate with Methyl radical
causes some convulsant activity [[METHOhexital]] only barb we really use; use it for pts undergoing ECT
55
What cant Barbiturates be used in people with porphyria
Barbiturates induce enzymes -ALA synthetase which controls the production of heme; induce ALA synthetase stimulate heme production NOT good for patient with porphyria who has an enzyme disorder in the heme biosynthetic pathway

Pharmacology (7 decks)

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