DrVirgo
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The distribution of elimination half-life of theophylline for adults (solid) and children (striped). Which of the following characteristics of children best explains these data?
A) Hepatic metabolism is faster
B) Oral absorption is poorer
C) Renal secretion is lower
D) Theophylline is less potent
E) Volume of distribution is larger
Please EXPLAIN the answer. Thanks. 
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| robin082006
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A
We see that after 8h, the drug is eliminated completely in Children but only about 50% in adults. This mean the drug is eliminated faster, therefore, possible choices are: increase renal secretion, increase liver metabolism.
So only choice A is suitable.
Any idea?
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| r_albayunen
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ill go with A
maybe since the drug requieres less volumen of distribution (child) to tissues its metabolism is faster ... 
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| DrVirgo
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The drug is eliminated faster in most children (3 hours) than in adults (7 hours)...
so I go with A) Hepatic metabolism is faster (in children)
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| mjl1717
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as I remeber the cytochrome p450 mixed funtion oxidase system is more active in the child so Im also going with answer-a [after the fact]
as far as distractors:
oral absorbtion is the same[this part of pharmacokinetics]eg.taking pills or liquid by mouth.
theophylline maintains same potency in a child or adult but levels are checked periodically. Potency means closer to y axis.
renal secretion should be about the same. [a model here would be comparing glucose, inulin, PAH creatinine secretion and reabsorbtion, but exactly where does theophylline fit in. either way the secretion should be about the same.
VD is amt of RX given/ plasma conc....high Vd -low plasma conc. and vice versa. If drug is bond to plasma protein Vd will be low. under normal conditions the % of free active drug in the plasma should be the same in child and adult. {excluding acetylation defects}
Lastly t1/2 is equal to 0.7 /elim. rate constant.
Edited by mjl1717 on 05/07/06 - 04:56 PM
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| DrVirgo
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Agree... I think the P450 system slows down in the elderly, and they metabolize drugs much slower, so they must be given a smaller dose compared to adults.
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| mjl1717
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Oh yes, Dr. Virgo! {drug regimens in a nursing home would confirm that.}
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| DrVirgo
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