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pharmacology exam 2 > Barbiturates > Flashcards

Barbiturates Flashcards

1
Q

Do Barbiturates cause areflexia?

A

No! Little to no effects on any muscles

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2
Q

Name the uses of barbiturates (6)

A

Seizure treatment, short painless procedures, induction, increased ICP, cardio version, ECT

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3
Q

What determines the effects of the barbiturates?

A

The molecule substitutions

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4
Q

Do oxybarbiturates have a long or short duration of action?

A

Long

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5
Q

Comment on thiobarbiturates lipophilicity, onset, duration of action

A

Lipophilic, rapid onset, shorter DOA

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6
Q

Methohexital has a longer or shorter DOA?

A

shorter

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7
Q

Phenobarbital has what key use?

A

Anticonvulsant

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8
Q

Which 4 receptors can barbiturates act on? What is the primary receptor?

A

GABA (primary), adenosine, nicotinic Ach, glutamate

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9
Q

Are barbiturates appropriate in patients with increased ICP?

A

Yes - decrease CBV, CBF, CMRO2, and ICP. Neuroprotective due to reverse steal (ischemic areas still get BF), free radical scavenging, liposomal membrane stabilizing, excitatory amino acid blockade
Dose required may cause significant hypotension

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10
Q

Contraindication of barbiturates? Why?

A

Acute intermittent porphyria

due to accelerated heme production

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11
Q

What happens and what do you do if a barbiturate is accidentally administered into an artery?

A

Area vasoconstricts -> blanching -> cyanosis -> gangrene -> necrosis -> permanent nerve damage
Dilute with lidocaine, give heparin, give papaverine, peripheral nerve block

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12
Q

Are barbiturates lipophilic?

A

Yes - rapid distribution, rapid termination after re-distribution

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13
Q

Do barbiturates undergo phase I or phase II metabolism?

A

Phase I - liver oxidation

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14
Q

Why is thiopental’s half life ten fold of that of propofol?

A

Thiopental has an active metabolite - pentobarbital (oxybarbiturate) - that is very long-acting

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15
Q

In what patients would half-time of barbiturates be affected?

A

Pediatrics - shorter half-time due to rapid hepatic clearance
Pregnancy - longer-half time due to protein binding

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16
Q

Do barbiturates cause pain on injection?

A

No - no additives

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17
Q

Do barbiturates cause an isoelectric EEG?

A

Yes - burst suppression

18
Q

What are the CV effects of barbiturates?

A

Decreased SVR, MAP, CO, direct myocardial depression

19
Q

What are the respiratory effects of barbiturates?

A

Cause central apnea (1 min) with return to baseline in 6 minutes which is shorter than with prop
some anti-bronchospastic effects with thiopental, but not as much as with prop
not as much bronchodilaton (airway reflexes maintained)
large doses can depress laryngeal/cough reflexes
Dose dependent depression of medullary and pontine ventilatory centers

20
Q

Enzyme induction from which barbiturate causes accelerated metabolism of which other drugs?

A

Phenobarbital.
Causes accelerated metabolism of tricyclics, anticoagulants, phenytoin, endogenous substances (vitamin K, bile salts, corticosteroids)

21
Q

What are the 4 stages of anesthesia that are produced with the induction of IV anesthetics?

A

There are no 4 stages with induction of IV anesthetics

22
Q

Is thiopental used for long-term sedation?

A

Not commonly - accumulation, prolonged half time, slow recovery

23
Q

How are the effects of thiopental terminated?

A

Very lipophilic - fast onset - quick re-distribution*

24
Q

What is thiopental’s hepatocyte? Does it cross the BBB?

A

hydroxythiopental - no, it is water soluble so it can be really excreted quickly

25
Q

What phase of metabolism does thiopental undergo?

A

Phase I (oxidation in the liver)

26
Q

Will liver injury impact the metabolism of thiopental?

A

No - you must have severe liver dysfunction to affect metabolism due to large reserve capacity of the liver to oxidize barbiturates

27
Q

Is half life longer or shorter than propofol?

A

Longer due to pentobarbital metabolite

28
Q

Is apnea likely with Thiopental?

A

Yes! Decreased sensitivity of ventilatory center to stimulation of CO2

29
Q

In terms of onset, effect time, half-life, and side effects, why would thiopental be less desirable than propofol?

A

Onset and effect time are similar (lipophilic = fast onset, rapid re-distribution = short effect time), but half-life is longer in thiopental due to pentobarbital and thiopental results in more N&V

30
Q

Induction dose of Thiopental for adults, pediatrics, and infants

A

Adults: 2.5-5.0 mg/kg IV
Peds: 5-6 mg/kg IV
Infants: 6-8 mg/kg IV

31
Q

In what 3 patients would you lower your induction dose of thiopental?

A

Elderly, early pregnancy, obesity

32
Q

If you pre-medicate with a benzo or opioid, what will you need to do with your dose of thiopental?

A

Decrease it

33
Q

Which 3 co-morbid states would you have to decrease your thiopental dose?

A

HF, shock, anemia

34
Q

Which is more potent, methohexital or thiopental?

A

Methohexital (2.7x)

35
Q

Methohexital is the induction agent of choice for which procedure?

A

ECT

Therapeutic effect is related to duration of the seizure

36
Q

Principle disadvantage of Methohexital?

A

Myoclonus

37
Q

How can you decrease the excitatory effects of Methohexital (hiccups and myoclonus)

A

Administer opioid

38
Q

Does methohexital have metabolites?

A

Inactive hydroxy derivatives

39
Q

What is clearance dependent upon for Methohexital? is it higher or lower than in thiopental?

A

liver blood flow
higher
results in shorter elimination half life

40
Q

What are the CV effects of Methohexital?

A

Less CV effects than with this due to tachycardia reflex response offsetting CV changes

41
Q

Induction dose of methohexital?
Rectal dose?
Infusion dose?

A

1-2mg/kg IV
25 mg/kg rectal
50-100 mcg/kg/min infusion

42
Q

Is methohexital appropriate for a patient on an anti epileptic?

A

No - lowers seizure threshold

pharmacology exam 2 (3 decks)

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