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rajeevkrishnadas

Old age - continuing queries

11 posts in this topic

Volume of distribution of a drug increases with old age... T/F

Manchester notes say True...

BUT

Body lean mass decreases; fat increases; body water decreases; decreased plasma protien binding...

That would make me think that the volume of distribution of water soluble drugs atleast decrease...

Please correct me if I am wrong...

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As far as my understanding goes this is a fairly typical part 2 question from the college as both answers could be correct. I'm actually more inclined to agree with the manchester notes and say true but it depends on the drug you are referring to.

The key point is whether or not the drug is lipophilic or hydrophilic.

Volume of distribution is equal to the total amount of the drug in the body divided by the blood concentration of the drug.

In the elderly body fat increases and so if your drug is lipid soluble it rapidly disappears from the blood into the additional fat. By the above equation volume of distribution then increases as your blood concentration drops relative to the dose administered.

If however your drug is water soluble then you have a relatively higher blood concentration than when you were young. The drug won't dissolve to the additional fat stores and stays within a smaller plasma compartment where it is less able to bind to protein. As such your blood concentration is higher and your volmue of distribution decreases.

So both could be right but I go for true simply because most of the drugs we use are lipid soluble (benzo's, psychotropics) and I think the key point the College wants us to know is that the elderly have relatively larger fat stores that drugs disappear into and therefore don't get eliminated from the body.

True to form its another example of an ambigious pointless College question that could be right or wrong depending on what you think the examiner is looking for.

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hopefully they will not ask these kind of questions...

I guess they may have noticed and corrected these kind of questions... but have been passed down by question banks...

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dorian

the question about the volume of distribution in elderly is given as true even in courses for part 1 as it's supposed to be related to the body fat percentage; consequently elderly store more drug and therephore need a lower dose

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dorian

the question about the volume of distribution in elderly is given as true even in courses for part 1 as it's supposed to be related to the body fat percentage; consequently elderly store more drug and therephore need a lower dose

The answer is probably true...

Because the Vd = amount of drug in the body/concentration in blood

Watersoluble drugs have a low Vd from the very start, because they stay in the blood.... and so the denominator is always high making the Vd low...

But since the water content in the body decreases with age, the concentration of drug in the blood increases, making Vd even less...

But like harsh and cmo said... i think Vd is less important for watersoluble drugs...

As a corollary... thats why lorazepam is longer acting than Diazepam, eventhough it has a shorter half life than diazepam... lorazepam is less lipid soluble and stays... but &nbsp:lol:iazepam is highly fat soluble, and redistributes itself very fast into the fat tissue, making its action very shortlived compared to lorazepam...

Thats why now lorazepam is the treatment of choice for status... and the fact that it is absorbtion is more reliable im compared to diazepam...

Cheers guys... please try the other questions I have posted...

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Please give reference... (other than exam notes) if possible

1. There is loss of astrocytes in normal aging _ T/F

2. Relapse of depression is more likely following ECT than with TCAs in elderly

3. Suicide in elderly is usually associated with drug and alcohol

4. Status spongiosus is a characteristic finding in the cortex of CJD

(is it the same as vacuolar degeneration or spongiform chane??)

5. Prion disease affect 1 person in 100,000 per year in the UK

6. There is a direct correlation between age at onset and number of CAG repeats in Huntingtons

(isnt it inverse correlation... ie the more number of repeats, the lower the age of onset)

7. Whipples disease is an infection that can result in dementia???

(wikipedia says cognitive deficits)

Same old question

8. Depression increases the risk of dementia

I think Manchester notes say if associated with pseudodementia - yes; if not false... but the college seminars says true and gives this reference... quite convincing...

&quot:lol:epressive symptoms occuring long before the onset of dementia have been shown to increase the risk of AD, and the longer an elderly person have depression, the higher the risk of cognitive decline or AD'

http://content.karger.com/ProdukteDB/produkte.asp?Aktion=ShowAbstract&ArtikelNr=22163&Ausgabe=225844&ProduktNr=224091

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Before this goes down the list into the next page...

Anybody... Crisps... anybody.... crisps.... (Marjorie Dawes - little britain)

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6. There is a direct correlation between age at onset and number of CAG repeats in Huntingtons

(isnt it inverse correlation... ie the more number of repeats, the lower the age of onset)

cant get enough crisps - you are correct about the inverese relationship. More cags = earlier illness

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