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Summer Pharm (2016) ** > Barbs > Flashcards

Barbs Flashcards

1
Q

What is more potent, a long branched chain or a straight chain?

Levo-isomers or dextro-isomers?

A

Long branched chain is more potent

Levo-isomers are twice as potent as dextro-isomers

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2
Q

‘Sodium something’ has a pKa of 3.8. Will this drug be more than 50% or less than 50% ionized at physiological ph?

A

Sodium is a positive molecule, so we can assume this is a weak acid (acids unite with positive ions).

A weak acid with a pKa of 3.8 at physiological pH means that we have fewer hydrogen ions than at equilibrium.

The ionized form will dominate.

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3
Q

Methohexital dose

A

1-2 mg/kg IV (induction)

20-30mg/kg in peds

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4
Q

base or acid?

opioids

barbs

benzos

ketamine

propofol

local anesthetics

A

opioid = weak base

barbs = alkaline in the bottle, acid at physiologic pH

benzos = bases

ketamine = base

propofol = acid

local anesthetics = base

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5
Q

Methyl radical on a barbiurates imparts what activity (methohexital)

A

CONVULSANT activity

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6
Q

which patients are at higher risk of allergic rxn

A

atopic patients (astmathics)

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7
Q

Barbiturates with __ at carbon #__ increases hypnotic activity

Barbiturates with __ at carbon #_ increases anticonvulsant activity

Having a _ increases convulsant activity

A

Branched chain at carbon #5 increases HYPNOTIC activity

Phenyl group at carbon#5 increases ANTICONVULSANT activity (phenobarbital)

Methyl radical increases convulsant activity (methohexital)

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8
Q

barbs

inadequate dosages (subtherapeutic) effects

A
  • stage 2 like response to airway manipulation (high risk of laryngospasm and bronchospasm)
  • paradoxical excitement
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9
Q

Barbiturates are ____ (acidic/alkaline) drugs, but when prepared in ____ solution, they are weak ___

A

They are acidic drugs

Prepared in highly alkaline solution (bacteriostatic)

Actually are weak acids, not bases

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10
Q

Other side effects not mentioned yet of barbs?

A
  1. Venous thrombosis
  2. Crosses placenta
  3. N/V
  4. Accelerated production of heme
    • by stimulation of an enzyme, D-aminolevulinic acid synthetase
    • caution in porphyria
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11
Q

Why is tolerance an issue with barbs?

A

As good enzyme inducers, they metabolize themselves well, tolerance builds, they need more drug for more effect,

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12
Q

Barbiturate MOA?

A

Decreases rate that GABA dissociates from receptor (increases duration of GABA), Cl channel opens

decreased postsynaptic sensitive to Ach, some muscle relaxation

Mimics GABA at receptor → DIRECTLY

Decreases trasmission in the sympathetic ganglia leading to hypotension

Depresses RAS -> sleep

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13
Q

Barbs

intra-arterial injection treatment

A
  1. dilute with NS
  2. phenoxybenzamine (direct acting alpha blocker)
  3. prevent thrombosis: heparin, urokinase
  4. brachial plexus or stellate ganglion block
  5. Papaverine (opium derivative -> vasodilator) 40-80 mg in 10-20 ml NS
  6. Lidocaine 1% 5-10 ml
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14
Q

Will induction be faster or slower when administering Thiopental to an acidotic patient?

Alkalotic?

A

Thiopental is an acidic drug with a pKa of 7.6

If the patient is acidotic, lower pH, means there are more Hydrogen ions available. With more ions available, the non-ionized form dominates and induction is FASTER!

If the patient is alkalotic, a higher pH, there are fewer Hydrogen ions available. With fewer ions available, the ionized form dominates and the induction is SLOWER!

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15
Q

All barbiturates are derived from what?

A

Barbituric acid urea and malonic acid

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16
Q

‘Something Sulfate’ has a pKa of 4.5, will this drug be more than 50% or less than 50% non-ionized at physiological pH?

A

Sulfate is a negative molecule, so we can assume this is a weak base (bases unite with negative ions).

A weak base with a pKa of 4.5 at physiological pH (above the pKa) means that we have fewer Hydrogen ions (more alkalotic) than at equilibrium.

The non-ionized form will dominate.

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17
Q

Induction of GA dosages for TPL and methohexital?

A
  • TPL 3-5 mg/kg IV (dec dose for elderly and first trimester pregnancy, inc dose for kids)
  • Methohexital 1-2 mg/kg IV or 20-30 mg/kg po in peds

Duration 5-8 min (that’s when it redistributes)

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18
Q

most potent hepatic enzyme inducer of the barbs

A

phenobarbital

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19
Q

Barbiturate respiratory effects?

A
  1. Depression of medullary and pontine ventilatory centers
  2. decrease response to hypoxia and hypercapnia
  3. APNEA
  4. Incomplete depression laryngeal and cough reflexes (laryngospasm, bronchospasm)
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20
Q

Drugs to avoid giving people with porphyria?

A
  1. Sulfonamide
  2. Etomidate
  3. Nifedipine
  4. Diazepam
  5. Phenytoin
  6. Barbs
  7. Alcohol
  8. Ketorolac

SEND Phil BAK (he’s unsafe)

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21
Q

Drugs safe in porphyria

A
  1. Opioid analgesics
  2. Narcan
  3. Propofol
  4. Ketamine (probably safe)
  5. Nitrous
  6. Succs
  7. Pancuronium
  8. Neostigmine
  9. Atropine
  10. Glycopyrolate
  11. Aspirin
  12. Acetaminophen
  13. Penicillin
  14. Glucocoticoids
  15. Insulin
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22
Q

Barbiturate pharmacokinetics?

A

Rapid onset

Redistribution is rapid, terminates effect

Extensive metabolism

Highly protein bound

Ionization of TPL: pK is 7.6

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23
Q

Methohexital contraindications

A

hx of seizures

pregnancy

porphyria

asthma

LR (it precipitates)

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24
Q

phenobarbital DOA

A

4-10 hrs

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25
Q

As a hepatic inducer, barbiturates increase metabolism of what drugs?

A
  1. Oral anticoagulants
  2. Phenytoin
  3. TCAs
  4. Corticosteroids
  5. Vit K
  6. Muscle relaxants? Look up.
26
Q

phenobarbital onset

A

5 min IV

20-30 min PO

27
Q

What happens if barbs are given intra-arterially?

A

IMMEDIATE, intense vasoconstriction and pain

Mechanism: crystalline precipitation in artery, inflammatory response, vasoconstriction, microembolization (loss of limb is possible!)

28
Q

Barbiturates

S.E.: myoclonus, hiccups, seizures

A

Methohexital

29
Q

Oxybarbiturates

  • have a __ at carbon #___
  • has what metabolism?

Thiobarbiturate

  • has a ____ at carbon #___
  • has what metabolism?
A
  • Oxy: O2 at carbon #2
    • hepatic metabolism only
  • Thio: Sulfur at carbon #2
    • hepatic and extra hepatic (GI) metabolism
30
Q

phenobarbital peak

A

30 min with IV

31
Q

What is porphyrin a precursor to?

A

Heme

which is a component of

  • hemoglobin
  • myoglobin
  • catalase
  • peroxidase
  • respiratory and P450 liver cytochromes
32
Q

Are barbiturates hepatic enzyme inducers?

A

YES, phenobarb is the most potent inducer

33
Q

methohexitol side effects

A
  1. induces seizures
  2. excitatory skeletal muscle effects (myoclonus)
  3. hiccups
  4. laryngospasm
  5. cough
  6. vasodilation, reflex tachycardia
  7. decreased CBF, ICP, CMRO2, isoelectric EEG
  8. histamine release (vasodilation, decreased BP, elevated HR)
  9. dose dependent resp depression
  10. decreased thershold for pain (antialgesia)
  11. CYP450 inducer
34
Q

Barbiturate CNS effects?

A
  1. Depress LOC
  2. Cerebral vasoconstriction, dec CBF, ICP, CMRO2, IOP
  3. Can produce isoelectric EEG (coma)
  4. Paradoxical excitement (sub-dose)
  5. anti-algesia: decreases pain threshold (small doses)
  6. Methohexital: myoclonus and hiccups
  7. Does NOT interfere with SSEP (somatosensory evoked potentials) monitoring
35
Q

What is porphyria?

A

Attacks precipitated by events that decrease heme concentration (drugs, hormones, fasting, stress) Autosomal dominant, linked to chromosome 11

36
Q

50% excreted unchanged in the urine

A

Phenobarbitol

37
Q

phenytoin class

A

anticonvulsant

antiarrhythmic class 1B

38
Q

Sulfuration increases what?

A

Sulfuration: fat soluble

As lipid solubility increases you get

  • shorter duration
  • more rapid onset
  • increased potency
39
Q

barb stimulate production of what enzyme?

A

D-aminolevulinic acid synthetase

can trigger prophyria

40
Q

Barbs1

metabolism dependent on hepatic enzyme activity, not hepatic blood flow

A

Thiopental

41
Q

Why is Thiopental stored in a very alkalotic solution?

A

Because, if Thiopental was stored in an acidic solution there would be more Hydrogen ions available and lead to a dominance of the non-ionized (protonated) form.

This is water insoluble and may form a precipitate.

42
Q

things that barbs don’t do

A

barbs DO NOT

  • take away EEG wave readings in ECT
  • alter SSEP (somatosensory evoked potentials) like inhalational agents do
  • cause muscle relaxation (you’ll need muscle relaxants)
  • affect baroreceptors (you’ll get reflex tachy due to drop in BP)
  • cause myocardial depression (it’s minimal, unless large doses are given, or SNS not intact, or hypovolemia)
43
Q

Thiopental side effects

A
  1. direct vasodilation (depression of medullary vasomotor center and decreased SNS outflow from CNS), reflex tachycardia
  2. decreased CBF, ICP, CMRO2, isoelectric EEG
  3. histamine release (vasodilation, decreased BP, elevated HR)
  4. dose dependent resp depression
  5. decreased thershold for pain (antialgesia)
  6. CYP450 inducer
44
Q

barbs

excreted in the urine and feces

A

Methohexital

45
Q

barbs redistribution time frame

A

Fat: blood coefficient is 11:1 → fast redistribution from brain to inactive tisues (muscle, fat)

  1. brain receives 10% of total IV done in 30-40 sec
    1. fast uptake (VRG)
  2. over the next 5 min there is a decrease in brain concentrations
    1. 2​nd uptake, primarily skeletal muscle (MG)
    2. decreased muscle mass = decrease the dose (elderly, trauma)
  3. after 30 min <10% of the initial dose is in the brain
  4. fat concetrantion rises for 30 min
46
Q

barbs

drug that is used as an anticonvulsant

why?

A

Phenobarbital

has a phenyl group at carbon #5

47
Q

barb with the lowest protein binding

A

Phenobarbitol 30%

48
Q

E1/2t in TPL vs methohexital?

A
  • Thiopental (TPL) 11.6h
    • Prolonged in pregnancy due to increased protein binding
  • Methohexital 3.9h
49
Q

barbs

metabolism dependent on C.O. and blood flow

A

Methohexital

50
Q

Phenobarbital side effects

A
  1. strongest CYP450 inducer of the barbs
  2. vasodilation with reflex tachycardia
  3. decreased CBF, ICP and CMRO2, isoelectric EEG
  4. dose dependent resp depression
  5. N/V
  6. bone marrow supression
  7. agranulocytosis
  8. thrombocytopenia
  9. megaloblastic anemia
  10. liver toxicity
  11. steven johnson syndrome
  12. ataxia
51
Q

barbs

alkalinization of urine doesn’t favor excretion, it shifts it to a more ionized state

A

Phenobarbital

52
Q

Barbiturate metabolism?

A

Side chain oxidation at carbon 5 to carboxylic acid terminates pharmacologic activity

Desulfuration, hydrolysis opens ring to water soluble compounds

Renal excretion

53
Q

Thiopental dose

A

3-5 mg/kg IV (induction dose)

5-6 mg/kg IV peds

7-8 mg/kg IV infants

increase dose in peds

decrease it in elderly and 1st trimester pregnacy

54
Q

Barbiturate CV effects?

A
  1. Depression of medullary vasomotor center and decreased SNS outflow
  2. peripheral vasodilation (dec afterload), dec preload Dec SBP -> compensatory HR increase
    • baroreceptors remain intact
  3. Minimal myocardial depression (more depression if SNS not intact, hypovolemia, or large doses)
  4. Histamine release with rapid IV admin (more hypotension)
55
Q

phenobarbital metabolism

A

50-60% unchanged in the urine

CYP450 hydroxylation and conjugation

56
Q

phenobarbital E1/2t

A

54-107 hrs

57
Q

Phenobarbital status epilepticus dose

A

10-20 mg/kg loading

5mg/kg Q 15-30 min until seizure is controlled

max dose 30mg/kg

58
Q

S/S of porphyria attack?

A

Severe abd pain, diarrhea, vomiting, ANS instability (tachycardia, HTN), electrolyte disturbances, seizure, resp failure, skeletal muscle weakness, neuropsychiatric disturbances

59
Q

Barbs interactions?

A
  1. Opioids
    1. alfentanil
    2. sufentanil
  2. catecholemines
  3. NMBs
    1. pancuronium
    2. vecuronium
    3. atracurium
  4. midazolam (these are acidic)
  5. LR solution is too acidic (precipitates)
60
Q

thiopental and pregnancy

A

prolonged elimination 1/2 t due to increased protein binding

61
Q

N/V of barbs compared to other classes of drugs

A

Higher incidence than Midazolam and Propofol

Lower incidence than Etomidate, Ketamine and volatile agents

Summer Pharm (2016) ** (17 decks)

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