Drug drug interaction
Dr. Asif Barejia
Drug drug interaction
A 66 years old technology consultant, Mr ABC, has a history of atrial fibrillation and his only chronic medication is Warfarin. One day, he had a dinner in a restaurant and the next day he develops diarrhoea. Doctor gave trimethoprim-sulfamethoxazole for the same.
He was feeling good in 4 days, and after 4 days he went into a party and had hew drinks. The next day he developed swollen right knee, a hemarthrosis . Lab studies showed elevated INR, which in a clinical setting is a marker for plasma warfarin level. The warfarin level was in supratherapeutic range. The question is, why did it happen?
Actually, when the drug co-trimoxazole was added in patient's chronic therapy of warfarin, it inhibited the metabolism of warfarin decreasing the clearance rate of warfarin and increasing its steady state concentration to suprathereutic level.
The effect was exacerbated by Ethanol intake which further inhibited warfarin metabolism.
This situation could have been avoided by measurin patient's INR levels and adjusting his warfarin dose. Also patient should had been advised about avoiding alcohol consumption while taking warfarin.
S●●●●●●●a M●●●●●●●●r and 83 others like this3 shares
Dr. G●●●●●s K●●●●●●i
Dr. G●●●●●s K●●●●●●i Pharmacology
Increased effect resulting from reduced warfarin clearance, displacement of warfarin from protein binding sites, alterations in gut flora.. The effect is known to occur even after 3 day course of sulphonamide.
Sep 12, 2016Like1
Dr. G●●●●●s K●●●●●●i
Dr. G●●●●●s K●●●●●●i Pharmacology
In additon to above, acute alcohol intake (>2-3 drinks) will further reduce warfarin clearance, thus elevtaing INR. The effect is short lasting so that warfarin blood levels may have come back to lower levels at the time of estimation, whereas effect on INR shall persist becoz it reflects some total od activity of hepatic procoagulant factor synthesis and their inhibition-a slow process!
Sep 12, 2016Like
D●●●●●●a m●●●o
d●●●●●●a m●●●o Ayurvedic Medicine
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Mar 14, 2019Like