can u sort out reasons??

[geethikachaudhary]

when drug 'A' is administered wid another drug 'B',plasma concentration profile of 'A' is observed to be lower than when 'A' is given alone....what can be possible reasons??

[Admin]

Competitive inhibition of absorption of A by simultaneous consumption of B ??

[geethikachaudhary]

yah ur ans is ryt...bt here as i din't mention the drug names/charecteristics of drug ans depends on individual's assumptions...

 here you hv assumed both drugs 'll absorb through same carrier mediated transport so due to competition for carriers between 'A' n 'B'.......('A') drug's absorption 'll decrease

fine lemme try for one more reason.....

assumptions:
'A' = weakly acidic drug
absorption site = in stomach
'B'=weakly basic drug(but strong enuf to change pH of stomach slightly)

based on this as 'A' is weakly acidic it 'll be unionised in acidic pH thus it 'll get absorb in stomach..bt when 'B' is administered there 'll be change in stomach pH occurs....so tht degree of ionisation increases n absorption decreases...

so ans for this question is not definite dat depends on our imagination.......lez see how many assumptions 'll be put forth here 

[Admin]

Similar to your assumption,
the drug A can be such that it gets absorbed from intestine and B changing the intestinal pH conditions !!

[Admin]

another assumption :

- Drug B make some complex with either A or any other enzyme /chemical involved in absorption of A ,and hence lowers its absorption

[geethikachaudhary]

hehe rehman bhai.....it seems u r goin to get winner trophy  ....no one else is participating too bad:(...

[sachin]

Let me also try my mind abilities here.

its given that Plasms concentration is lowered when A & B are simultaneously adminstered.
plasma concentration varies with lot many factors apart from the absorption rate, like the permeability of drug/partition coefficient, the metabolism profile and the excretion rate.

so if B has any effect in any of these paths then it will affect the plasma concentration of A.
like if B promotes activity of any enzyme that is responsible for the metabolism  of A then plasma level of A will lowers quickly.

[geethikachaudhary]

if 'B' decreases gastric motilitynty (ex: by anti cholinergic activity) thn absorption of 'A' decreases and hence its plasma concentration also will decrease..!!

[Admin]

if 'B' decreases gastric motilitynty (ex: by anti cholinergic activity) thn absorption of 'A' decreases and hence its plasma concentration also will decrease..!!

But this assumption doesnt fit into every type of drug. you have to mention the type of drug A and how its affecting.

if drug A is a drug which is absorbed from small intestine thn in this case a lower motility means more time for stay in the intestine and hence d drug will get more absorbed ,so your assumption fails in this case.

[razvi1002000]

Drug "A" is showing synergistic effect when given alongwith drug "B"