Term
| classification of barbituates |
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Definition
| long, intermediate, and ultra-short acting; misleading because residual drug in body after initial effects worn off. additional doses can convert ultra-sort to long acting. |
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Term
| Stability of barbituate solutions? |
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Definition
| thio-in frig up to 2 weeks; methohexital-frig up to 6 wks; thiopental stable in sterile solution for 6 days |
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Term
| name the 3 ultra-short barbituates? |
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Definition
| thiopental, thiamylal, methohexital; |
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Term
| Why are the barbituates incompatible with other solutions? |
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Definition
| They are available as sodium salts that are highly alkaline (thiopental pH is 10.5 in a 2.5% solution), incompatible with opiods, catecholamines and NMB-basic drugs which are acidic in solution. |
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Term
| What are the structural differences of oxybarbituates and thiobarbituates? |
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Definition
| The sedative-hpnotic properties result from substitution at the number 2 and 5 carbon atoms. Oxybarbituates (methohexital) replace the carbon atom 2 with oxygen, thiobarbituates (thiopental and thiamlal) replace with sulfur atom. Thiobarbituates have a greater lipid solubility therefore have greater hypnotic potency, faster onset, and shorter duration of action. |
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Term
| Mechanism of action of barbituates? |
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Definition
| inhibits neurotransmitter GABA, depress the reticular activating system. Depress transmission of nervous system ganglia->hypotension. High doses barbituates decrease sensitivity of postsynaptic membranes to acetylcholine. Barbituates and propofol decrease dissociation of GABA from receptor ->duration of opening of chloride channel |
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Term
| Prompt awakening after one dose of barbituates is from? |
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Definition
| redistribution from the brain to skeletal muscles and then to the fat. |
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Term
| Context sensitive half life of barbituates is prolonged because? |
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Definition
| drug is sequestered in the skeletal muscle and fat, then reenters the circulation. |
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Term
| Are Thiobarbituates more or less protein bound than oxybarbituates? |
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Definition
| More!, Thiopental has the highest protein binding. |
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Term
| Decreased protein binding can be due to what? |
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Definition
| displacement of drugs by ASA or phenybutazone, or other protein bound drugs. In uremic pts this may be due to competitive binding of nitrogenous wastes. Hypoalbuminemia may cause this decrease in cirrhosis. |
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Term
| distribution of barbituates determined by? |
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Definition
| lipid solubility (most important), protein binding, ionization (non-ionization) |
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Term
| How does hypovolemia affect the distribution of barbituates? |
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Definition
| It may decrease the blood flow to the skeletal muscles while blood flow to the brain and heart are maintained. This can result in exaggerated cerebral and cardiac depression. |
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Term
| How long does it take the barbituates to have maximal brain uptake? And then what happens? |
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Definition
| It takes 30 seconds. Within 5 minutes the concentration falls by 1/2 of its peak concentration. Therefore, redistribution is the mechanism for early awakening. |
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