Acute ingestion of alcohol will decrease the metabolism
, causing the INR to increase. Chronic (daily) alcohol ingestion induces live enzymes that accelerate the metabolism of coumadin, causing the patient to require more coumadin.
A couple of drinks at a summer barbecue isn't a problem---it'll thin your blood a little more. A whole bottle by yourself in one night is a bit excessive and you may get into trouble. Not only will your blood be thinner, but you won't have the usual coordination that you have and may hurt yourself. Try alternating nonalcoholic drinks with your glasses of wine.