Barbiturates Flashcards by Megan Manasco

Barbiturate derived from

Barbituric acid

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Are all barbiturates racemic mixtures?

Yes

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Sulfuration substitution means

Greater lipid solubility

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Phenylephrine group replacement results in

Anticonvulsant properties

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Methyl group replacement results in

Convulsive activity

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For barbituric acid to have CNS effects what must occur?

Substitution at #2 and 5 carbon

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3 uses for barbiturates

1- induction of anesthesia
2- tx of elevated ICP
3- ECT, retrobulbar block, cardioversion

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Clinical use of barbiturates declining because of (4)

1- lack of specificity and CNS effect
2- lower therapeutic index
3- greater tolerance and liability for abuse
4- high risk of drug interactions

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Major drawback of barbiturates for anesthetic

Hang-overs

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Methohexital and seizure threshold

Decreases seizure threshold

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R/t increased risk of dose related excitatory phenomena like myoclonus and hiccups

Methohexital

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Recovery rate of methohexital

Awake in 3-7 minutes

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Induction dose of methohexital

1-2mg/kg

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Methohexital dose to induce anesthesia in peds and uncooperative

20-30mg/kg rectally

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ECT dose of methohexital

1 mg/kg

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Half life of thiopental.

Anesthesia application

11.5-26 hours

Slow emergence

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Sodium thiopental r/t hemodynamics

Large doses cause hemodynamic instability

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Thiopental is dosed by

Ideal Body Weight

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Thiopental induction dose

3-5mg/kg

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Barbiturates quick awakening is due to

Redistribution

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Slow wake up of thiopental is due to

Redistribution from peripheral tissues to central resulting in hang-over effect

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Barbiturate complete elimination from body is dependent on what?

Metabolism

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Effect site equilibration time of thiopental and methohexital is

Rapid

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Barbiturate lipid solubility is determined by

Solubility of non-ionized molecules

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Barbiturates and plasma protein binding -which binds more

High plasma protein bound Thiopental greatest (72-86%)

Most lipid soluble and possess greater anesthetic potency (barbs)

Non-ionized barbiturates

3 that determine barbiturate pharmacokinetic

- lipid solubility - protein binding - ionization

Shock = decreased skeletal muscle perfusion. What change to barb dose?

Decrease dose

Principal mechanism for barbiturate early awakening

Redistribution from central to peripheral compartments

Main initial site for distribution of barbs

Skeletal muscle

Only compartment where thiopental concentrations continue to increase 30 minutes post injection

Fat = hang-over

Effect of acidosis on barbs effect

Increases effect

Alkalosis effect on barbiturate effects

Decrease effects

Non-ionized barbiturates result in

- greater CNS access | - greater lipid solubility

Metabolism of oxibarbiturates

Hepatic metabolism only

Metabolism of thiobarbiturates

Mainly hepatic but also kidney and CNS

Metabolites of barbs

Inactive

Capacity of liver to metabolize barbiturates

Large capacity

Thiopental metabolism

Slow | 10-24% metabolized every hour

Most rapid metabolism of barbiturates? Why?

Methohexital - lower lipid solubility so less plasma protein bound, more available for metabolism

determines complete recovery from barbs

Metabolism

Peds pt have _______ recovery from barbs due to ________

Faster recovery r/t more rapid hepatic clearance

Elimination 1/2 time of thiopental greater in _________ r/t

Greater in obese patients due to greater VD form more fat storage

All barbs are filtered by renal glomeruli but ________ limits filtration

High protein binding

____________ favors reabsoption of drugs back into blood

High barbiturate lipid solubility

__________ of barbs eliminated in us-metabolized form

Less than 1%

Enzyme induction stimulation from barbiturates persists for

Up to 30 days after last dose

Enzyme induction of barbs results in greater metabolism of

``` Coumadin Dilantin TCA Corticosteroid Vit K ```

Barbs interact with _______ in CNS- causing

GABA- increased duration of GABA activated chloride channels

________ very sensitive to barb effects compared to other tissues

CNS

Barbs and SNS

Depresses SNS= lower BP | High dose = circulatory collapse

Tolerance to sedative effect of barbs occurs at greater rates than anti convulsants and lethal effects so

Barbiturate therapeutic index decreases as tolerance increases

Pt on highly protein bound meds (ASA, Dilantin) and thiopental effects

Increased thiopental effects

Barbs effect on CNS

CNS depressant | Range from mild sedation to total anesthesia

Barbs effect on cerebral blood volume by

Decrease CBV by cerebral vascular vasoconstriction

Barbs good or bad for elevated ICP

Good for high ICP

Barbs and cerebral flow

Intense cerebral vasoconstriction

Barbs and EEG

Isoelectric EEG max depression of CMRO2 by 55%

High dose barb to lower ICP results in

Hypotension and worsen cerebral perfusion pressure

Thiopental causing isoelectric EEG results in

Peripheral vasodilation and myocardial depression

Focal ischemia protection from barbs useful in what cases

CEA Thoracic aneurysm Profound hypotension

Small barb dose _______ pain threshold

Lowers

Thiopental and EP

Do not interfere with EP monitoring

At what dose thiopental is there no visible myocardial depression in healthy pt

5mg/kg

Barbs have ______ inotropic effects at high doses

Negative

Barbs and BP

Lower BP

Hypovolemic pt and barbs

Should not get barbs

Give barbs______ | Why?

Quick | Slower admin results in higher total dose

Laryngeal and cough reflexes with barbs

Do not depress laryngeal and cough reflexes

Barbs and medullary and pontine ventilatory centers

Depression

Greatest barb for hepatic enzyme inductions

Phenobarbital

Cirrhosis and barbs

Exaggerated response, bc more free drug to elicit effects

Less than _____% of barbs eliminated unchanged

Barbs and GI tract

Well absorbed from GI tract

Main site of redistribution of barbs from central compartment

Skeletal muscle

Barbs and skeletal muscle relaxation

Does not occur

Allergic rx with barbs Seen in

Very rare Prior thiopental exposure IgE mediated hypersensitive disorder

Thiopental allergic reaction mortality

High

Diseases of accelerated heme production resulting in jaundice

Porphyria

Barbs effect on porphyria

Symptoms exaggerated

Barbs and porphyria patients

CONTRAINDICATED

Neonates and barbs

Greater sensitivity bc less protein binding sites

If give thiopental in artery

Gangrene and nerve damage

Venous thrombosis after barb administration for induction is due to________ not__________

Deposition of barbiturate crystals NOT alkaline pH (10)

Best advantage of thiopental over propofol

Thiopental mixtures are strongly bactericidal