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Pharmacology > Barbs > Flashcards

Barbs Flashcards

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]]

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

A

MORE EFFECT
pKa 7.6 acidic drug

alkaline preparation but drug is ACID

if pt alkaloid less effect

25
Q

“what are barbiturates affects on BP?”

A

DIRECT Acting

decreases transmission in sympathetic ganglia

can also mimic and enhance GABA on GABAa

26
Q

Which drug provided ‘hangover effect’

A

Thiopental [[pentothal]]

27
Q

What drug is prolonged in pregnant women

A

Thiopental

increased protein binding

28
Q

What drug used to be given to provide cerebral protection in cardiac OR for pt going on bypass

A

Thiopental

29
Q

Which drug causes excitatory skeletal muscles

A

Methohexital

[[hiccups and clonus]]

30
Q

[[Autonomic]] SNS is NOT intact in what situations

A

Extremes of age;
elderly and babies

hypovolemia

REALLY large dose

^^these situations decrease dose to avoid severe drop inBP and myocardial depression

31
Q

Other Effects of Barbiturates

A

-can cause venous thrombosis

32
Q

Effects on Placenta

A

crosses placenta

babies born a little more sedated

33
Q

what will happen if patient on PO Barbiturate for seizure disorder

A

will RAPIDLY metabolize drugs
2-3x as fast

*especially MUSCLE relaxants
[[use longer acting]]

34
Q

Nausea / vomiting incidince

A

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
Q

Tolerance to Barbiturates

A

develops RAPIDLY

switch peoples seizures meds from one barb to another

hepatic enzyme inducers of their own cells [[start metabolizing very quickly]]

36
Q

Effects on Hepatic Enzymes

A

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
Q

Allergies to Barbiturates

A
  • not very common
    1: 30,000

if it did occur
HIGH MORTALITY

usually occurred in atopic patients
[[**asthma; autoimmune]]

38
Q

Why cant we mix Barbiturates with other things

A

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
Q

Whats happens if Barbiturate accidentally gets injected ARTERIALLY?

A

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
Q

How do you treat and accidental injection of Barbs into arteries

A

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
Q

Porphyrias

A

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
Q

Most important Porphyrins in humans

A

heme; main precursor of hemoglobin

43
Q

Biggest problem with Prophyria

A

accumulation of heme is VERY TOXIC to tissues in high concentrations

44
Q

Other facts about Porphyria

A
  • 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
Q

Porphyrias triggered by

A

**most important trigger are drugs

some hormones

some event that increases heme concentration

46
Q

Drugs that trigger Porphyrias

A

Barbiturates
[[thiopental, methohexital]]

Etomidate

Pentazocine

47
Q

S/S of Porphyrias

A

-severe ab pain with diarrhea and vomiting

  • ANS instability
    [[tachycardia, HPN]]

-electrolyte disturbances
[[EKG changes]]

  • skeletal muscle weakness
  • respiratory failure
  • seizure
  • neuropsych disturbances
48
Q

When do we use Methohexital

A

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
Q

Why is methohexital good for electric shock therapy

A

 Methyl radical imparts convulsant activity (methohexital)
 some convulsant activity in brain

Does not produce flat line on EEG
[[no isoelectric EEG]]

50
Q

Only barbiturate we really use

A

METHOHEXITAL

51
Q

Barbiturate with substitution at Carbon 5

A

sedative and hypnotic prosperities

52
Q

Barbiturate with branch chain at Carbon 5

A

INCREASES hypnotic activity

53
Q

Barbiturate with Phenyl group at Carbon 5

A

INCREASES ANTIseizure activity

[[PHENObarbital]]

54
Q

Barbiturate with Methyl radical

A

causes some convulsant activity
[[METHOhexital]]

only barb we really use;
use it for pts undergoing ECT

55
Q

What cant Barbiturates be used in people with porphyria

A

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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