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Summer Pharm (2016) ** > Barbs > Flashcards

Flashcards in Barbs Deck (61)
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1

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

Levo-isomers or dextro-isomers?

Long branched chain is more potent

Levo-isomers are twice as potent as dextro-isomers

2

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

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.

3

Methohexital dose 

1-2 mg/kg IV (induction)

20-30mg/kg in peds

4

base or acid?

opioids

barbs

benzos

ketamine

propofol

local anesthetics

opioid = weak base

barbs = alkaline in the bottle, acid at physiologic pH

benzos = bases

ketamine = base

propofol = acid

local anesthetics = base

5

Methyl radical on a barbiurates imparts what activity (methohexital)

CONVULSANT activity

6

which patients are at higher risk of allergic rxn

atopic patients (astmathics)

7

Barbiturates with __ at carbon #__ increases hypnotic activity

Barbiturates with __ at carbon #_ increases anticonvulsant activity

Having a _ increases convulsant activity

Branched chain at carbon #5 increases HYPNOTIC activity

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

Methyl radical increases convulsant activity (methohexital)

8

barbs

inadequate dosages (subtherapeutic) effects

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

9

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

They are acidic drugs

Prepared in highly alkaline solution (bacteriostatic)

Actually are weak acids, not bases

10

Other side effects not mentioned yet of barbs?

  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

11

Why is tolerance an issue with barbs?

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

12

Barbiturate MOA?

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

13

Barbs

intra-arterial injection treatment

  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

14

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

Alkalotic?

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!

15

All barbiturates are derived from what?

Barbituric acid urea and malonic acid

16

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

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.

17

Induction of GA dosages for TPL and methohexital?

  • 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)

18

most potent hepatic enzyme inducer of the barbs

phenobarbital

19

Barbiturate respiratory effects?

  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)

20

Drugs to avoid giving people with porphyria?

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

SEND Phil BAK (he's unsafe)

21

Drugs safe in porphyria 

  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

22

Barbiturate pharmacokinetics?

Rapid onset

Redistribution is rapid, terminates effect

Extensive metabolism

Highly protein bound

Ionization of TPL: pK is 7.6

23

Methohexital contraindications

hx of seizures

pregnancy

porphyria

asthma

LR (it precipitates)

24

phenobarbital DOA

4-10 hrs

25

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

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

26

phenobarbital onset 

5 min IV

20-30 min PO

27

What happens if barbs are given intra-arterially? 

IMMEDIATE, intense vasoconstriction and pain

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

28

Barbiturates

S.E.: myoclonus, hiccups, seizures

Methohexital

29

Oxybarbiturates

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

Thiobarbiturate

  • has a ____ at carbon #___
  • has what metabolism?

  • Oxy: O2 at carbon #2
    • hepatic metabolism only
  • Thio: Sulfur at carbon #2
    • hepatic and extra hepatic (GI) metabolism

30

phenobarbital peak

30 min with IV