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15 Cards in this Set
- Front
- Back
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Barb uses?
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Sedation
Sleep Decrease ICP Head injury cases |
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good induction agents for head injury [4]
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thiopental, etomidate, propofol or midazolam
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Barb formation facts
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Pka and salt formation (insoluble free base to soluble sodium salt) pH and pKa considerations
How make salt? NaOH To keep in free base form. pH of solutions around 10If allowed to react with carbonic acid from water and CO2, precipitation of insoluble salts. |
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barb SAR
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Thio higher potency/onset/shorter duration because more lipid soluble
Nitrogen substitution gives potential for enantiomers/diastereomers but given as racemic mixtures. |
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Pharmacodynamics
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Interacts with GABAA alpha
inhibits glutamate Receptor -Voltage Gated Ion Channels -Sodium/Calcium/Potassium -adenosine receptors -Nicotinic Acetylcholine Receptors (nAChR) |
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BARB S/A'S
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Normovolemic have small decrease in bp.
Hyperanalgesic, increase reaction to painful stimuli at subanesthetic doses. Methohexital has incidence of hiccups and coughing. Thiol compounds cause release of histamine from mast cells. BP due to peripheral vasodilation and heart rate may increase to compensate in the hypovolemic patient, can cause hypotension. Can slowly titrate with success. |
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barbitureate ADME
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Distribution is quick
Thipental 10% to brain in 30 seconds and in 5 minutes brain concentration down by _ and 30 min down to 30% because of redistibution Quick to brain because high perfussion Reduces the activity – not because of elimination but distribution --- multi-compartment model---? graph Secobarbital with most lipophilic distributes quickly and Phenobarbital with least lipophilic distributes the slowest Readily cross placenta and into breast milk Distribution to fat does not necessarily affect awake time unless large dose or repeated dosing and then groggy awake |
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ADME oxy vs Thio
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Oxybarbiturates: onset parallels the rate of absorption and duration parallels elimination.
Thiobarbiturates: onset and duration are more closely related to the pattern of distribution. Distribute rapidly into brain (quick onset) Distribute rapidly into muscle then fat (quick offset) |
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Protein Binding
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Protein binding is high since lipophylic
Liver diseas or hypoalbuminemic states – less protein binding so more drug free and concentration up Thiopental 72-86% |
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Metabolism
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100% P450 Metabolism
Amobarbital Butabarbital Pentobarbital Secobarbital 75% P450 Metabolism Phenobarbital/Pentobarbital |
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Metabolism Concerns
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Induce Microsomal Enzymes
High clearance of other drugs Tricylic anti-depressants Corticosteroids used for asthma control Coumadin anti-coagulants Estrogen/Progesterone Digitoxin MAOIs have drug-drug interaction |
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Excretion
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Renal Excretion
Excretion of metabolized drug Lipophilic character so have re-absorption High protein binding limits filtering Phenobarbital only drug of class that has any significant excretion without being unchanged Elimination half time governed by hepatic reactions Higher protein binding during preganancy |
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barb Contraindications
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Sensitivity to barbituric acid analogs
Porphyria Respiratory depression/insufficiency (asthma) Renal Impairment Hepatic Impairment Sleep Apnea Suicide Potential Pain Addictions Ketamine Pregnancy |
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contraindication rationale
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Sensitivity – some are allergic and thio analogs can cause histamine release
Porphyria – accumulation of porphyrins, increase aminolevulinic acid synthetase activity which increases porhyrin synthesis, which causes abdominal pain, nuerotoxicity, autonomic dysfunction, peripheral and intercostal and phrenic nerve damage. Respiratory depression – causes further depression and can cause apnea. Reduces sensitivity of respiratory center to CO2 Renal impairment – mostly renal excretion Hepatic Impairment – mostly metobolized by liver so if impaired, have higher doses. Addictions – seem to become addicted only if previously addicted to other things. Not really a true “high” Ketamine – severe respiratory depression if used at same time Pregnancy – amobarbital in first trimester has lead to significant malformations (heart, club foot, etc.) but if have patient with epilepsy, probably must continue and phenobarbital seems to be best |
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Anesthesia Considerations
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Lower MAC
Not depress laryngeal reflexes |
