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Pharm II > Test 1: Barbiturates > Flashcards

Test 1: Barbiturates Flashcards

1
Q

What is Barbituric Acid?

A

Barbituric acid is pharmacologically inert, but substitutions at the C5 position impart hypnotic activity.
-Branched sidechains have a greater hypnotic activity than straight chains
-Sulfur substitution = sodium thiopental. It was the mainstay for the intravenous induction of anesthesia before the introduction of propofol.
-No analgesic properties
-Lost popularity due to associated with hang-over, narrow therapeutic index, and evolution of new drugs (propofol)

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2
Q

Substituting a Phenyl Group at C5 on Barbituric Acid causes what?

A

Anticonvulsant activity
-Used in pediatrics
-Ex: Phenobarbital

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3
Q

Substituting a Methyl Group at N1 on Barbituric Acid causes what?

A

-Shortens DOA
-Increases potency
-Increases excitatory effects
-Increases convulsive activity (used in ECT)
-Ex: Methohexital

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4
Q

Substituting a Suflur Atom at C2 on Barbituric Acid causes what?

A

-Increases lipid solubility
-Increases anesthetic potency
-Increases onset of action
-Ex: Sodium Thiopental

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5
Q

Substituting an Oxygen Atom at C2 on Barbituric Acid causes what?

A

“Oxybarbiturate”
-Secobarbital (Seconal)

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6
Q

What was THE intravenous induction agent for anesthesia prior to Diprivan (Propofol)?

A

Thiopental
-Production in the U.S. stopped in 2010 over controversy associated with thiopental’s use in lethal injection.

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7
Q

What are the general symptoms associated with the use of Barbiturates?

A

-Sedation, Hypnosis
-EEG slowing to burst suppression
-Decreased CMRO2
-Anticonvulsant (Thiopental)
-Myocardial depression
-Decreased vascular resistance
-Respiratory depression
-Excitatory motor effects (Methohexital)

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8
Q

What occurs when barbiturates are mixed with nonbasic solutions such as normal saline?

A

Barbiturate sodium salts require a pH greater than 10 to remain in aqueous solution and precipitate readily when mixed with nonbasic solutions such as normal saline solution.

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9
Q

What occurs when Barbiturates are combined in high concentrations with certain weak bases such as neuromuscular blockers?

A

They also precipitate when combined in high concentrations with certain weak bases such as the neuromuscular blockers, forming a “conjugate
salt” (e.g., sodium thiopental and rocuronium bromide precipitate to form sodium bromide).

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10
Q

Describe the Pharmacokinetics of Thiopental?

A

-Onset of action: 30-60 seconds (extremely lipophilic)
-Duration of action: 5-30 minutes (!)
-The subsequent decline in concentration results primarily from redistribution to other tissues rather than metabolism and elimination
-Highly protein bound (75-90%) in the plasma to albumin (affected by decreased albumin levels)
-Metabolized into Pentobarbital (only an issue in prolonged, high-dose administration) via Hepatic and Renal
-1/2 life = 3-11 hours

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11
Q

What is the induction dose for adults and children of Sodium Thiopental (Pentothol)?

A

Adults: 3-5 mg/kg
Children: 5-6 mg/kg

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12
Q

What are contraindications to the use of Barbiturates?

A

-Hypersensitivity
-Porphyria

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13
Q

What is Porphyria?

A

A disorder of the enzymes that participate in the production of porphyrins (protein essential for hemoglobin function) and heme.
-Results in the buildup of the chemicals that produce porphyrin
-Genetic condition

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14
Q

What are the Acute S/Sx of Porphyria?

A

-Severe abdominal pain/distention
-Pain to chest, legs, back
-Constipation, diarrhea, vomiting
-Increase BP/palpitations
-Insomnia, anxiety, restlessness
-Seizures
-Breathing problems
-Muscle weakness, paralysis
-Red or brown urine

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15
Q

What is the MOA of Sodium Thiopental (Pentothol)?

A

1) Potentiates GABA’s effect
2) Blocks excitatory effect of Glutamate at AMPA and kainate receptor subtypes, but not at NMDA receptors.
3) Inhibits Neuronal Nicotinic (Ach) Receptors

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16
Q

What are the neurological effects of Sodium Thiopental (Pentothol)?

A

-Dose dependent CNS depression
-Decreases CMRO2
-Decreases CBF & ICP
-Anticonvulsant Effects!

17
Q

What are the Cardiovascular effects associated with the Barbiturates?

A

-Venodilation
-Decreased preload and CO

Pronounced decrease in MAP and CO post induction.
-Negative inotropic effects
-Reflex increase in HR r/t baroreceptor reflex.

18
Q

What are the Renal Effects of Sodium Thiopental (Pentothol)?

A

Intraoperative oliguria due to reduced renal blood flow and GFR

19
Q

What are the Respiratory Effects of Sodium Thiopental (Pentothol)?

A

-Releases histamine!!! Risk for broncho/laryngospasm
-Depresses respiratory center

20
Q

What are the injection related effects of the administration of Sodium Thiopental (Pentothol)?

A

-Pain on injection
-Precipitates if pH<10

21
Q

What are the main uses for Sodium Thiopental (Pentothol)?

A

-Neurosurgery (Considered to be neuroprotective)
-Cesarean Section (10 minute window to deliver infant)

22
Q

What order kinetics is exhibited by Sodium Thiopental (Pentothol)?

A

IV Infusion is 1st order kinetics (has a 1/2 life)

When given in very high doses (bolus), thiopental can even exhibit “zero-order kinetics,” wherein metabolic capacity is saturated, grossly prolonging the duration of action.

23
Q

What is the difference between zero order and first order kinetics?

A

0 order kinetics: drug is eliminated per unit time (ex: Alcohol and hangover. Same portion is eliminated each hour).

1st order kinetics: drug is eliminated per unit of the concentration of the drug. (Ex: 100% to 50% to 25% to 12.5%, etc.). Have half-lives.

24
Q

What are the Pharmacokinetics of Methohexital (Brevital)?

A

-Onset of action = immediate (Maximal brain uptake in 30 seconds)
-Duration of Action = 4-7 minutes (!)
-The subsequent decline in concentration results primarily from redistribution to other tissues rather than metabolism and elimination
-73% protein bound
-Metabolism = Hepatic
-Half-life = 4 hours

25
Q

What is the induction dose for Methohexital (Brevital)?

A

-Adults: 50-120 mg (1-1.5 mg/kg IV from Katzung)
-Children: 1-2 mg/kg IV
-Preop IM 5-10 mg/kg
-Rectal 25 mg/kg (!)

26
Q

What is the MOA of Methohexital (Brevital)?

A

1) Potentiates GABA’s effect
2) Blocks excitatory effect of Glutamate at AMPA and kainate receptor subtypes, but not at NMDA receptors.
3) Inhibits Neuronal Nicotinic (Ach) Receptors

27
Q

What are the neurologic effects associated with Methohexital?

A

-Dose dependent CNS depression
-Decreases CMRO2
-Decreases CBF & ICP
-Lowers the seizure threshold (!)

“Flow-Metabolism Coupling” leads to “reverse steal” effects. Ideal for focal, not global neuro injuries.

28
Q

What are the renal effects associated with Methohexital?

A

Reduced renal blood flow

29
Q

What are the respiratory effects associated with Methohexital?

A

-Hiccoughs
-Decreases respiratory center

30
Q

What are the injection related effects associated with the administration of Methohexital?

A

-Myoclonus
-Pain on injection

31
Q

What are the uses for Methohexital?

A

-Electroconvulsive Therapy
-Pediatric Anesthesia

32
Q

For what populations should you reduce the dose of Barbiturates?

A

-Use of pre medications can reduce required induction dose by 50%
-Elderly
-HF
-Liver Failure (Decreased proteins)
-Shock
-Anemia
-Obesity

33
Q

Erroneous thiopental administration arterially can lead to what?

A

The formation of crystals, which can cause vasospasm and thrombus formation.
-Can lead to severe tissue injury involving gangrene
-Tx: SNS blockade (Stellate ganglion block) in the involved extremity +/- Lidocaine local injection

34
Q

What is the induction dose of Methohexital (from Katzung)?

A

1 - 1.5 mg/kg IV

35
Q

What is the DOA of Methohexital (katzung)

A

4-7 minutes

36
Q

What is the induction dose of Thiopental (katzung)?

A

3-5 mg/kg IV

37
Q

What is the DOA of Thiopental (Katzung)?

A

5-10 min

38
Q

How are Barbiturates metabolized?

A

Thiopental and methohexital undergo hepatic metabolism, mostly by oxidation but also by N-dealkylation, desulfuration, and destruction of the barbituric acid ring structure.

39
Q

Why are Barbs C/I in patients with Porphyria?

A

Barbiturates should not be administered to patients with acute intermittent porphyria because they increase the production of porphyrins through stimulation of aminolevulinic acid synthetase.

Pharm II (24 decks)

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