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Pharm Test 2 > Benzos and Barbs > Flashcards

Benzos and Barbs Flashcards

1
Q

5 Phamacological effects of benzodiazepines?

A
  • Anxiolysis
  • Sedation
  • Anterograde amnesia
  • Anticonvulsant action
  • Muscle relaxation (spinal level)
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2
Q

Do benzos produce enough muscle relaxation for surgery?

A

No

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3
Q

Do benzos alter dose of muscle relaxant needed?

A

No

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4
Q

Which is great, potential for abuse in opioids or benzos?

A

Benzos potential for tolerance/ abuse is less

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5
Q

Do benzos induce hepatic enzyme?

A

No

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6
Q

What is antagonist for benzos?

A

Flumazenil

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7
Q

What is structure of benzodiazepines?

A

Benzene ring fused with 7 member diazepine ring (2 rings fused)

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8
Q

What is MOA of benzos?

A

Facilitate action of Gaba at GABAa -Increases affinity of GABAa for its receptor -DO NOT activate GABAa receptor

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9
Q

What is affect of increase affinity for GABAa by benzos?

A

-Opening Cl gated channels -Increase Cl conductance -Hyperpolarization of post-synaptic membrane -increased resistance of post-synaptic membrane to excitation

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10
Q

What is principle inhibitory neurotransmitter in CNS?

A

GABA

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11
Q

What causes differences in different benzos?

A

-Potency -Lipid solubility -Pharmacokinetics Generally all are highly lipid soluble and highly bound to plasma proteins

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12
Q

Which plasma proteins do benzos bind to?

A

Albumin

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13
Q

Properties of midazolam?

A

-Water soluble preparation -Imidazole ring -2-3x potency of diazepam - Extensize first pass effect -90-98% protein bound -Rapid redistribution–> short duration

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14
Q

Effect site equilibrium and t 1/2 elimination of midazolam?

A
  • 0.9-5.6 min effect sit eequilibration - 1-6.5 hours t 1/2 elimination
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15
Q

What is metabolism of midazolam?

A

-Extensive hepatic metabolism -Hydroxylation to water soluble compounds (1 and 4 hydroxymidazolam) -ACTIVE METABOLITE= 1-hydroxy-midazolam -Conjugated and excreted in urine -Renal failure DOES NOT affect vd, t 1/2 elim, or clearnace

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16
Q

CNS effects of midazolam?

A

-Decrease CBF, CRMO -Does NOT produce isoelectric EEG -Preserves cerebrovascular response to CO2 - Does NOT attenuate ICP in response to laryngoscopy -Potent anticonvulsant and amnestic -Paradoxical excitement- RARE

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17
Q

Respiratory effects of midazolam

A
  • Dose dependent decrease in ventilation -Hypoxemia and hypoventilation is enhanced when given with opioid -Depress swallowing refelx -Decrease upper airway activity
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18
Q

Cardiovascular effects of midazolam

A

-Decreases SVR at induction dosage -BP Consequently decreases -CO unchanged -Doesn’t prevent HR and BP changes with intubation

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19
Q

Premedication PO dose for midazolam?

A

0.25-0.5 mg/kg PO, masx PO dose for peds 20mg

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20
Q

IV sedation dose for midazolam?

A

1-2.5 mg IV can give as high as 5mg if needed

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21
Q

Induction dose midazolam?

A

0.1-0.2 mg/kg over 30-60 seconds Maintenance: incremental or infusion

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22
Q

Properties of diazepam?

A
  • Highly lipid soluble with prolonged DOA - Commercially prepared in organic solvents including propylene glycol, benzyl alcohol VERY PAINFUL IV AND IM -Highly protein bound -Rapidly absorbed from GI tract (PO valium better than PO versed) -Viscous, pH 6.6-6.9
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23
Q

Metabolism of diazepam

A
  • Oxidation, n-demethylation to desmethyldiazepam, oxazepam, and temazepam by hepatic microenzymes -Conjugated to glucaronic acid prior to renal excretion -Desmethyldiazepam - oxidized, conjugated and excreted in urine -Cimetidine will impact metabolism of valium
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24
Q

Elimination 1/2 time of diazepam?

A

21-37 hours in healthy volunteers Desmethyldiazepam- 48-96 hours

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25
Q

Pharmacodynamics of valium?

A

Cardiac stable= SVR, BP , CO (<20% decrease) Other system effects similar to midazolam

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26
Q

Premed oral/IV dosage for valium?

A

10-15 mg PO 0.2/kg for IV (reduces MAC)

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27
Q

Induction dose valium?

A

0.5-1.0 MG/KG IV

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28
Q

Anticonvulsant dose for valium?

A

0.1 mg/kg IV Inhibit activity in hippocampus and limbic system

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29
Q

Properties of Ativan?

A

Lorazepam 5-10x more potent than diazepam - NO ACTIVE METABOLITES - Most potent of bnzs in anethesia practice -Hurts IV d/t propylene glycol - less influenced by alteration in hepatic function, age and other drugs

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30
Q

t 1/2 life for lorazepam

A

10-20 hours

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31
Q

Onset of lorazepam?

A

peak 2 hours (not very utilized in OR setting)

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32
Q

Premed/PO dose for lorazepam?

A

50 mcg/kg (MAX 4MG)

33
Q

What is flumazenil?

A

Imidazobenzodiazepine derivative -Specific competitive benzos antagonist with high affinity for bnz receptors - No adverse S/E

34
Q

DOA of flumazenil

A

30-60 minutes, may need to repeat/supplement

35
Q

Dose of flumazenil

A

0.2 mg IV initial, wait 2 min 0.1 mg IV subsequent doses at 60 second intervals MAX 3 MG

36
Q

Infusion dose of flumazenil?

A

0.1-0.4 mg/hr (0.1-0.5 mcg/kg/min)

37
Q

How is flumazenil metabolized?

A

Hepatic metabolism and renal excretion

38
Q

Why does flumazenil not cause acute anxiety and neuroendocrine stress response?

A

Flumazenil mimics benzos

39
Q

What other use is flumazenil used for?

A

Antiabuse- alcohol/benzos

40
Q

Properties of barbiturates?

A
  • Sodium salts -Highly alkaline- bacteriostatic but NATURE of drug is acid (acidic pt, acidic drug= more nonionized= reduce dose) - Racemic mixture, but levo isomer is potent one -Derived from barbituric acid -Urea+malonic acid= barbituric acid
41
Q

Barbiturates with substitutions at carbon #2, #5 have what?

A

Sedative, hypnotic properties

42
Q

Barbiturates with branches chain at #5 increases which activity?

A

Hypnotic

43
Q

Phenyl group at C#5 on barbituate increases which activity?

A

anticonvulsant activity

44
Q

Methyl radical on barbiturate imparts ____ activity.

A

Convulsant (used in ECT)

45
Q

What does sulfuration do to barbiturates?

A

Increases fat solubility -Shorter duration of action -More rapid onset -Increased potency

46
Q

Long branched chain on barbiturate is ____ potent than straight chain

A

More

47
Q

Potency of levo isomers vs destro isomers?

A

Levo isomers are 2x potent of dextro-isomers

48
Q

If oxygen is at C#2, we call the barbiturate a ______

A

oxybarbiturate

49
Q

If sulfur at #2, we cal the barbiturate a _____

A

thiobarbiturate

50
Q

What is relative potency of the barbiturates?

A

Thiopental- (TPL/STP)=1 Thiamylal (Surital)=1.1 Methohexital (Brevital)= 2.5

51
Q

MOA of barbiturates?

A
  • Decreases rate at which GABA dissociated from its receptor–> increases duration of GABA activated Cl- opening (enhances GABA activity) -Mimics GABA at receptor (direct activation of Cl-channels) -Decreases sympathetic ganglia- hypotension -Decreases postsynaptic membrane sensitivity to ACh–> some muscle relaxation -Produces functional inhibition of post-synaptic neuron -Depresses RAS (Reticular activating system)
52
Q

Pharmacokinetics of barbiturates?

A

-Rapid onset of aciton (one arm–> brain) -Redistribution= rapid termination of effect -Extensive metabolism

53
Q

TPL Protein binding/fat:blood partition coefficient? ionization?

A
  • TPL 70-85% protein bound F/B coefficient= 11 Ionization TPL pK= 7.6 (mainly non-ionized at physio pH)
54
Q

What type of metabolism does oxybarbiturates go through

A

hepatic only

55
Q

What type of metaboism does thiobarbiturates go through?

A

hepatic+ some extra hepatic (GI)

56
Q

How is pharmacological activity of barbiturates terminated?

A

Side chain oxidation at C#5 to carboxylic acid

57
Q

How is barbiturate ring opened?

A

Desulfuration Hydrolysis

58
Q

How are barbs ultimately excreted?

A

Changed to water soluble compound during metabolism -Renal excretion primarily <1% excreted unchanged Methohexital also excreted in feces

59
Q

Does CO/HBF have any effect on barbs?

A

Methohexital is more influenced by HBF compared to TPL

60
Q

What is T 1/2 elimination TPL or methohexital?

A

TPL= 11.6 hours Prolonged in pregnancy due to increased protein binding Methohexital= 3.9 hours

61
Q

CNS effects of barbs?

A
  • Depress LOC - Cerebravasoconstriction, reduced CBF, decreased ICP, and CMRO2 -Can produce isolectric EEG - Paradoxical excitement -Methohexital can cause excitatory skeletal movemnets (myoclonus and hiccups) -Does not preclude SSEP monitoring -Small doses decrease pain threshold (anti analgesic) -No skeletal muscle relaxation -Decrease IOP -Cerebral protection
62
Q

CV effect of barbs?

A
  • Depression of medullary vasomotor center & decreased SNS outflow form CNS–> peripheral vasodilation–> preload decreases -SBP decreases, compensatory increase HR in normovolemic patients -Myocardial depression is minimal - If SNS not intact OR hypovolemia OR large doses given to reduce ICP will see SIGNIFICANT decrease in BP and myocardial depression - Histamine release with rapid IV admin
63
Q

When is SNS not intact?

A

“Extremes of age” i.e. elderly and children If SNS not intact, can see significant decrease in BP and myocardial depression with barbs

64
Q

Respiratory effects of barbs?

A
  • Dose dependent depression of medullary and pontine ventilatory centers - Decreased ventilatory response to hypoxia and hypercapnia -Apnea -Depression of laryngeal and cough reflexes are incomplete (can cause laryngospasm/bronchospasm)
65
Q

Other special effects of barbs?

A

Hepatic enzyme induction with chronic use, phenobarb is most potent inducer! -Increase metabolism of oral anticoags, phenytoin, TCA, corticosteroids and vit K. -Accelerated production of heme by stimulation of enzyme d-aminolevulinic acid synthetase -Venous thrombosis -Readily crosses placenta

66
Q

What can we expect with patients treated with barbs for sz disorders?

A

-Metabolize drug about 2x as fast as expected -Especially evident in muscle relaxants

67
Q

Barbituates N&V incidence?

A

Higher than midaz and propfol but lower than etomidate, ketamine and volatiles

68
Q

Tolerance and barbituates?

A

Tolerance develops rapidly Induction of hepatic enzymes, dose requirements may increase 6 fold

69
Q

Allergies with barbituates?

A

1:30,000 HIGH mortality - Presents as anaphylaxis -Allergy in atopic pt (mulitple allergies, asthma, previous TPL exposure)

70
Q

Induction dose for TPl and methohexital?

A

TPL 3-5 mg/kg - decreaes dose with age (30% decrease in elderly) and first trimester (protein bound) - Increase dose in peds (5-6 mg/kg); infanct 7-8 mg/kg Methohexital -1-2 mg/kg IV OR 20-30 mg/kg PR in peds

71
Q

Duration of single dose barb for IV induction? Why?

A

5-8 minutes d/t rapid redistribution

72
Q

How to prepare barbs?

A

DO NOT mix with LR–> precipitate Only use sterile H2O and NSS Dont’ mix with opioids, catechols, NMB, midazolam, which are acidic

73
Q

What happens during intra-arterial injection of barbs? What to do with intra-arterial injection barb?

A
  • Immediate intense vasoconstriction and pain -Crystalline precipitation in arterial vessel, inflammatory response, vasoconstriction, microembolization Treatment - dilute with NSS - Phenoxybenzamine- alpha antagonist -Prevent thromosis - heparin, urokinase -Brachial plexus or stellate ganglion block (block SNS response) -Papaverine (Vasodilates) 40-80 mg in 10-20 mL or 5-10 mL lidocaine 1%
74
Q

What is porphyrias?

A

-Group of inborn errors of metabolism: deficiency in enzymes in heme biosynthetic pathway -Triggers when there’s an event that decreases heme concentration in body will cause accumulation of precursors of heme

75
Q

What does porphyrins do in humans?

A
  • Main precurors of heme- essential constituent
76
Q

What is gene expression of porphyria

A

-Non-sex linked autosomal dominant, variable expression (chromosome 11) -Attacks more frequent in femalse, 3rd 4th decade)

77
Q

S/S of porphyria

A
  • Severe abdominal pain with D/V - ANS instabiity- tachycardia, HTN -Electrolyte disturbances -Skeletal muscle weakness, respiratory failure -Seizure -neuropsychiatric disturbances
78
Q

Triggers for porphyria

A

Thiopental Thiamylal Methohexital Etomidate

79
Q

What do barbs increase metabolism of?

A

oral anticoags, phenytoin, TCA, corticosteroids and vit K

Pharm Test 2 (3 decks)

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