jean robert
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A 64 yo female is treated with warfarin for chronic AF.She develops acute pyelonephritis that requires ceftriaxone therapy.Soon after initiation of therapy her lab testing reveals significantly increase PT and INR.Warfarin action is increased in this patient due to effect on which of the following?
a.-Absorption
b.-Competitive antagonism
c.-Plasma protein binding
d.-Hepatic metabolism
e.-Renal excretion
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| new_n_lost
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b.-Competitive antagonism
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| drhouse
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i m not sure about the ans but Goodman n gillman says.
In addition to an effect on reducing intestinal flora, cephalosporins containing heterocyclic side chains also inhibit steps in the vitamin K cycle.
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| tompat
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had it been competitive antagonism PT and INR wud have gone bananas
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| drhouse
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D. Hepatic metabolism
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| mjl1717
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i like answer-b
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| tompat
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cud any 1 explain y competitive antagonism?
doesn't it mean that some where it is competing with warfarin and reducing it's action i.e. to prolong PT AND INR. so these two should be reduced, if it is antagonism. i know that some of the cephalosporins cause hypoprothrobinemia and thus prolonging the PT/INR.
ceftriaxone also alters the intestinal flora so that vit.K production is interfered and warfarins action is potentiated.
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| jean robert
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B ( competitive antagonism) is the correct answer.
Warfarin normally inhibits vit K dependent carboxylation of glutamic acid residues of clotting factor II,VII,IX,X (mnemonic 1972) , protein C and protein S through its action on the enzyme EPOXIDE REDUCTASE.
On the other hand, we need to remember that vit K occurs in 2 natural forms: K1 or phylloquinone (from dietary sources) and K2 or menaquinone ( produced in the gut by BACTERIAL flora)
So, antibiotic use results in a decrease in a intstinal bacterial flora and consequent under production of vit K2. Therefore, it diminish the competitive inhibition.
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| drhouse
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hey jean roberts i got yr explanation,
but in one book i red that cephalosporin affect metabolism of the warfarin. i dont remember name of the book but it was like that. thats why i chose D.. wot do u say.
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| ssrpk
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why is it caled competitive antagonism, does'nt make sense, its simply enhancing warfarin's toxicity...wheres the antagonism?
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| drhouse
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Mr ssrpk, jean s explanation makes perfect sense.
warfarin compete with the vitamin K for the enzyme epoxide reductase.
now if we decrease the production of vitamin K by decreasing intestinal bacterial floara, more enzyme will be available for the warfarin. hence increasing its effect.
thats why we give vitamin k in bleeding due to warfarin.
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| new_n_lost
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ssrpk wrote:
why is it caled competitive antagonism, does'nt make sense, its simply enhancing warfarin's toxicity...wheres the antagonism?
Coumarins inhibit hepatic synthesis of the vitamin K–dependent coagulation factors II, VII, IX, and X and the anticoagulant proteins C and S. Typically, vitamin K is a cofactor in the postribosomal synthesis of the clotting factors mentioned above. The vitamin K–dependent step involves carboxylation of glutamic acid residues and requires regeneration of vitamin K to its reduced form.
Coumarins and related compounds prevent vitamin K from reducing to its active form. The degree of effect on the vitamin K–dependent proteins depends on the dose and duration of treatment with warfarin.
Thus Penicillins and Cephalosporins Compete with Warfarin to Inhibit the Vit K. The Antagonism is bw Warfarin and Cephalosporins for Vit K. This is a UW question thats how they have come up with Answer,
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| tompat
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Thus Penicillins and Cephalosporins Compete with Warfarin to Inhibit the Vit K. The Antagonism is bw Warfarin and Cephalosporins for Vit K. This is a UW question thats how they have come up with Answer,
this thing i never came across on internet also.
competitive antagonist is the one which will bind to the same receptor and DECREASE the action of agonist. warfarin here is inactiviting VIT k so is the cephalosporin.so its gotta be competitive agonism cause the action of both is the same.
again the raised PT n INR show agonism.
guys voice ur opinion lets not just accept answer which aint convincing, correct me if i m wrong
but as the few good men said DONT U COME DOWN FLASH UR BADGE(U WORLD) N MAKE ME NERVOUS.
Edited by tompat on 07/02/07 - 09:25 PM
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| drhouse
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Thus Penicillins and Cephalosporins Compete with Warfarin to Inhibit the Vit K. The Antagonism is bw Warfarin and Cephalosporins for Vit K. This is a UW question thats how they have come up with Answer,
I didnt know such definition of competitive antagonism,
thanks new n lost for improving my knowledge
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| jean robert
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tompat, in the question stem we re asked to give the mechanism responsible for the increase of warfarin activity. The obvious answer ( after this long discussion) is the ALTERED competitive antagonism.
Now, as you know, Vit K reverses the action of Warfarin. That s why they give vit K for warfarin toxicity. I wanna assume that s the competitive antagonism.
So, antibiotics (like cephalosporins) that affect the intestinal flora ( source of vit K) decrease the production Vit K and bla bla bla
Take home message
Normally, there s a competitive antagonism between Warfarin and Vit K. This competitive antagonism gonna be affeted by taking antibiotics which destroy intestinal flora (source of vit K).
That s my sense about the question.
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| tompat
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wow makes perfect sense.
i was ignoring altered antagonism, right jean u made it clear.
good work.hope u wont mind my constant questioning.
thank u. 
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| new_n_lost
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 I thought u were challenging Badge Tompat 
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| tompat
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hi nnl,
as u said
Thus Penicillins and Cephalosporins Compete with Warfarin to Inhibit the Vit K. The Antagonism is bw Warfarin and Cephalosporins for Vit K. This is a UW question thats how they have come up with Answer,
this shows that u believe there is antagonism bet warfarin and cephalosporin.
as per my understanding and explanation above there aint any antagonism.
as jean explains it , it is the altered state of competition between vit k and warfarin.
if ur quoting uworld and want to accept their explanation it's ur choice!
lets keep this discussion healthy.
happy studying buddy
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| new_n_lost
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Tompat .................. This is so Funny I can very well Remember that u were essentially saying same thing in 3 long posts wht one person said in one and still U disagreed with them.
And THe Same Thing over here I have said essentially the Same thing as Jean has.
But i guess for u the thing is that u can only find that explanation correct if U & Urself can understand it and then agree with it and disregard all the other explanations which in one way or the other r saying the same thing.
I said My Last Comment in faith of keeping this Discussion Healthy But I think U got Lost In Translation of the Quoted Material.
Dont Take it Personally and Literally as Nobody does over here on the Forum
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FORUM RULES-- Those who believe in telekinesis, raise my hand. I get enough exercise just by pushing my luck --P4U World.." The pure and simple truth is rarely pure and never simple."
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| tompat
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oh ok, may be the electronic media is causing the misunderstanding. as we cant associate our tones to our comments.
if ur talking about my that post where i went on to explain with long ans, i never disagreed with jean. i said that he was wrong in thinking that he is wrong in thinking too much
i just wanted other members to give their ans without jeans ans affecting their choices.
hope u understand this.
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