WBR0519: Difference between revisions

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|MainCategory=Pharmacology
|MainCategory=Pharmacology
|SubCategory=Gastrointestinal, Hematology
|SubCategory=Gastrointestinal, Hematology
|Prompt=A 62 year old male patient on immunosuppressive therapy with a past medical history significant for a recent bioprosthetic mitral valve replacement, systolic heart failure, hypertension, and hyperlipidemia, presents to the physician’s office for black-colored stools.  The patient’s medications are metoprolol, ramipril, warfarin, simvastatin, fenofibrate.  He has stopped taking aspirin against medical advice one year ago.  The patient explains that he recently had a bacterial infection and had started antibiotic therapy.  During work-up, INR was measured to be 8 (Therapeutic range: 2-3).  Which of the following antibiotics most likely contributed to the patient’s gastrointestinal bleeding symptoms?
|Prompt=A 62 year old male patient on immunosuppressive therapy with a past medical history significant for a recent bioprosthetic mitral valve replacement, systolic heart failure, hypertension, and hyperlipidemia, presents to the physician’s office for black-colored stools.  The patient’s medications are metoprolol, ramipril, warfarin, simvastatin, fenofibrate.  He has stopped taking aspirin against medical advice one year ago.  The patient explains that he recently had a bacterial infection and had started antibiotic therapy.  During work-up, INR was measured to be 8 (therapeutic range: 2-3).  Which of the following antibiotics most likely contributed to the patient’s gastrointestinal bleeding symptoms?
|Explanation=Patients receiving warfarin therapy, such as the case in mechanical valve replacement, must be monitored for possible bleeding at all times using INR.  Introduction of new medications must always take into account the possible interaction with warfarin.  P-450 inhibitors will prevent the elimination of warfarin  in the liver and cause prolonged effects and possible bleeding, On the other hand, P-450 inducers will hasten warfarin elimination and predispose the patient to thrombotic events.
|Explanation=Patients receiving warfarin therapy, such as the case in mechanical valve replacement, must be monitored for possible bleeding at all times using INR.  Introduction of new medications must always take into account the possible interaction with warfarin.  P-450 inhibitors will prevent the elimination of warfarin  in the liver and cause prolonged effects and possible bleeding, On the other hand, P-450 inducers will hasten warfarin elimination and predispose the patient to thrombotic events.


Among the list of antibiotics, ciprofloxacin is an inhibitor of P-450 system.
Among the list of antibiotics, ciprofloxacin is an inhibitor of P-450 system.
Drugs that inhibit P-450 (and cause more warfarin bleeding effect): Macrolides, amiodarone, isoniazid, cimetidine, ritonavir, ciprofloxacin, ketoconazole, sulfonamides, gemfibrozil, quinidine.  
Drugs that inhibit P-450 (and cause more warfarin bleeding effect): Macrolides, amiodarone, isoniazid, cimetidine, ritonavir, ciprofloxacin, ketoconazole, sulfonamides, gemfibrozil, quinidine.
 
|AnswerA=Ciprofloxacin
|AnswerA=Ciprofloxacin
|AnswerAExp=Ciprofloxacin is an inhibitor of P-450 system, thus causing less warfarin elimination and more systemic effect and possible bleeding.
|AnswerAExp=Ciprofloxacin is an inhibitor of P-450 system, thus causing less warfarin elimination and more systemic effect and possible bleeding.
|AnswerB=Amoxicillin  
|AnswerB=Amoxicillin
|AnswerBExp=Amoxicillin is not classically associated with P-450 inhibition.
|AnswerBExp=Amoxicillin is not classically associated with P-450 inhibition.
|AnswerC=Rifampin
|AnswerC=Rifampin
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|AnswerD=Chloramphenicol
|AnswerD=Chloramphenicol
|AnswerDExp=Chloramphenicol is not classically associated with P-450 inhibition.
|AnswerDExp=Chloramphenicol is not classically associated with P-450 inhibition.
|AnswerE=Clindamycin
|AnswerE=Clindamycin
|AnswerEExp=Clindamycin is not classically associated with P-450 inhibition.
|AnswerEExp=Clindamycin is not classically associated with P-450 inhibition.

Revision as of 04:02, 7 October 2013
Author [[PageAuthor::Rim Halaby, M.D. [1]]]
Exam Type ExamType::USMLE Step 1
Main Category MainCategory::Pharmacology
Sub Category SubCategory::Gastrointestinal, SubCategory::Hematology
Prompt [[Prompt::A 62 year old male patient on immunosuppressive therapy with a past medical history significant for a recent bioprosthetic mitral valve replacement, systolic heart failure, hypertension, and hyperlipidemia, presents to the physician’s office for black-colored stools. The patient’s medications are metoprolol, ramipril, warfarin, simvastatin, fenofibrate. He has stopped taking aspirin against medical advice one year ago. The patient explains that he recently had a bacterial infection and had started antibiotic therapy. During work-up, INR was measured to be 8 (therapeutic range: 2-3). Which of the following antibiotics most likely contributed to the patient’s gastrointestinal bleeding symptoms?]]
Answer A AnswerA::Ciprofloxacin
Answer A Explanation AnswerAExp::Ciprofloxacin is an inhibitor of P-450 system, thus causing less warfarin elimination and more systemic effect and possible bleeding.
Answer B AnswerB::Amoxicillin
Answer B Explanation AnswerBExp::Amoxicillin is not classically associated with P-450 inhibition.
Answer C AnswerC::Rifampin
Answer C Explanation AnswerCExp::Rifampin is an inducer of the P-450 system. As a result, warfarin will be eliminated faster; the patient will be predisposed to thrombotic events.
Answer D AnswerD::Chloramphenicol
Answer D Explanation AnswerDExp::Chloramphenicol is not classically associated with P-450 inhibition.
Answer E AnswerE::Clindamycin
Answer E Explanation AnswerEExp::Clindamycin is not classically associated with P-450 inhibition.
Right Answer RightAnswer::A
Explanation [[Explanation::Patients receiving warfarin therapy, such as the case in mechanical valve replacement, must be monitored for possible bleeding at all times using INR. Introduction of new medications must always take into account the possible interaction with warfarin. P-450 inhibitors will prevent the elimination of warfarin in the liver and cause prolonged effects and possible bleeding, On the other hand, P-450 inducers will hasten warfarin elimination and predispose the patient to thrombotic events.

Among the list of antibiotics, ciprofloxacin is an inhibitor of P-450 system. Drugs that inhibit P-450 (and cause more warfarin bleeding effect): Macrolides, amiodarone, isoniazid, cimetidine, ritonavir, ciprofloxacin, ketoconazole, sulfonamides, gemfibrozil, quinidine.
Educational Objective:
References: ]]

Approved Approved::No
Keyword WBRKeyword::ciprofloxacin, WBRKeyword::warfarin, WBRKeyword::bleeding, WBRKeyword::bleed, WBRKeyword::interaction, WBRKeyword::P-450, WBRKeyword::P450, WBRKeyword::inhibitor, WBRKeyword::inducer, WBRKeyword::inhibition, WBRKeyword::induction, WBRKeyword::GI bleeding, WBRKeyword::black, WBRKeyword::stools, WBRKeyword::gastrointestinal
Linked Question Linked::
Order in Linked Questions LinkedOrder::
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