guys need help xm in 2 weeks....nbme 5, sec 3, q 1 - raihansomcn

[ArchivalUser]

does any one know how to calculate this question....looking at the plasm cone..nor its a first order neither o order elimination....any one can explain ...plz

[ArchivalUser]

can any one plz....zen....can u plz help me...

[ArchivalUser]

OK, So you have to find out the plasma half life (t1/2) of the drug from the information given in the Q. You see, at 1PM the plasma conc is 240 ng/mL. Then at 5 PM it is 120 ng/mL. So, the plasma conc decreased by half (t1/2) during 4 hr. So t/2 is 4 hr.

Now, you need 4-5 t1/2 for the drug concentration to be below 5% (95% will be excreated by that time. (Please go through Kaplan Pharma 2010 page 14)

Instead, just do a math like this,

Plasma conc. of 240 ng/mL-------------- 0 hr
120----------------------4 hr
60------------------------8 hr
30-----------------------12 hr
15-----------------------16 hr
7.5 (below 10)----------20 hr
So the ans should be DDD, 20 hr.

Thanks.

[ArchivalUser]

okay dear friend :

as desperatehh explain that is absolutely correct with full details :

question states child overdose and gives u a table of numbers:
left side gives u time* not hours* and right side gives u level of drug in plasma*

so you obviously know that 240ng/ml is what the current level of diphenhydramine is within this girls plasma.....but you have to figure out the half life of the drug basically when this drug reached HALF of its original level in plasma....

so at 5 pm when the doctors checked the level again this patients level was 120 ng/ml makes sense because 240 / 2 = 120 right so @ this point we now know this is the half life....

one fact we NEED TO KNOW *** IS majority of the drugs are first order elimination.... which means constant fraction being eliminated....

so 50% of drug loss was @ around 5 pm when started from 1 pm which was the original level now whats the difference in hours ? 4 hours.... it took doctors 4 hours to find out that the level of this drug was @ half.....


now what you have to do is figure out when will this drug get below 10 ng / ml as the question ask you so u work it out....


currently @ 0 hours its 240....
then @ 4 hours in its 120
then 50% loss of 120 at another 4 hours = 60
then another 50% loss of 60 which remained in the plasma @ 4 hours = 30
then another 50% loss of 30 which remained in the plasma @ 4 hours = 15
then another 50% loss of 15 which remained in the plasma @ 4 hours = 7.5

[ArchivalUser]

now all you have to do is take all the 4 hours you used.... in this case you used

5 [4 hours]

and then u simply multiply : 5 x 4 hours = 20 hours.... hope this helped pal goodluck!!

[ArchivalUser]

Nice detailed explaination, zen.

Thanks

[ArchivalUser]

great...sorry guys i asked the same question twice....i got it.....thanks.....pray for u is all what i can do....

[ArchivalUser]

desperatehh thank you dear friend...


@raihansomcn its okay and godbless thanks thats all we need in return friend

[ArchivalUser]

may god help us....thanks again...