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Q: Most dangerous interactions with warfarin ( Answered 5 out of 5 stars,   0 Comments )
Subject: Most dangerous interactions with warfarin
Category: Health > Medicine
Asked by: omnitemm-ga
List Price: $15.00
Posted: 06 Sep 2003 09:55 PDT
Expires: 06 Oct 2003 09:55 PDT
Question ID: 252911
What are the most dangerous drug interactions with warfarin that you
could be subject to if you experiment with different supplements such
as vitamins, minerals, amino acids, smart drugs, prescription
medications and so on?

Are there any medical conditions such as viral infections of the liver
which in turn disable coagulation factors that could be especially
dangerous for a person taking warfarin?

With dangerous I mean for example: one otherwise considered normal
dose of a supplement very quickly causes a great prolongation of
prothrombin time.
Subject: Re: Most dangerous interactions with warfarin
Answered By: bobbie7-ga on 06 Sep 2003 13:45 PDT
Rated:5 out of 5 stars
Hello Omnitemm,  

Important Disclaimer 

Answers and comments provided on Google Answers are general
information, and are not intended to substitute for informed
professional medical or other professional advice.

I've organized a digest of links to information and articles  
related to what you listed in your question. I have included short
excerpts but I highly recommend you read the articles in their

Millions of Americans each day take warfarin (also known as Coumadin)
— a medication that decreases the body's ability to form blood clots.

Thomas H. Lee, M.D.
Harvard Medical School

The Coumadin (warfarin sodium) Page

The Department of Neurology at Massachusetts General Hospital provides
information on the effects on INR listed by specific drugs, classes of
drugs and medical conditions.

Drugs by Class
Either view all drug classes which increase/decrease PT/INR...
Specific Drugs Reported

Either view all specific drugs which increase/decrease PT/INR...

Other factors that may affect PT/INR
Either view all other factors which increase/decrease PT/INR...

Department of Neurology at Massachusetts General Hospital

Top Ten Dangerous Drug Interactions in Long-Term Care

Warfarin — NSAIDs 

Aleve, Anaprox, Anaprox DS, Ansaid, Arthrotec, Cataflam, Clinoril,
Daypro, diclofenac, diclofenac/mistoprostrol, diflunisal, Dolobid,
etodolac, Feldene, flurbiprofen, ibuprofen, Indocin, Indocin SR,
indomethacin, ketoprofen, ketorolac, Lodine, Lodine XL, mefenamic
acid, meloxican, Mobic, Motrin, nabumetone, Naprelan, Naprosyn,
naproxen, Orudis, Oruvail, oxaprozin, piroxicam, Ponsel, Relafen,
sulindac, Tolectin, Tolectin DS, tolmetin, Toradol, Voltaren, Voltaren

Potential for serious gastrointestinal bleeding

Warfarin — Sulfa drugs 

Sulfa drugs 
Bactrim DS, Bactrim SS, Cotrim DS, Cotrim SS,
erythromycin/sulfisoxazole, Gantanol, Gantrisin, Pediazole, Septra DS,
Sulfatrim, sulfamethizole, sulfamethoxazole, sulfisoxazole, Thiosulfil
Forte, trimethoprim/sulfamethoxazole

Increased effects of warfarin, with potential for bleeding

Warfarin — Macrolides 

Coumadin, warfarin  azithromycin, Biaxin, clarithromycin, Dynabac,
dirithromycin, E-Mycin, erythromycin base, EES, erythromycin ethyl
succinate, Ery-Tab, Eryc, EryPed, Erythrocin, erythromycin stearate,
Ilosone, erythromycin estolate, Pediazole, erythromycin/sulfisoxazole,
Tao, troleandomycin, Zithromax

Increased effects of warfarin, with potential for bleeding

Warfarin — Quinolones

Coumadin, warfarin  alatrofloxacin, Avelox, Cipro, ciprofloxacin,
enoxacin, Floxin, gatifloxacin, Levaquin, levofloxacin, lomefloxacin,
Maxaquin, moxifloxacin, Noroxin, norfloxacin, ofloxacin, Penetrex,
sparfloxacin, Tequin, trovafloxacin, Trovan, Trovan IV, Zagam

Increased effects of warfarin, with potential for bleeding

Warfarin — Phenytoin
(Dilantin, phenytoin)

Increased effects of warfarin and/or phenytoin

The Multidisciplinary Medication Management Project

American Medical Directors Association
Top 10 Particularly Dangerous Drug Interactions in Long Term Care

Drug Herb Interactions


“Patients on warfarin (coumadin) are most at risk for problems from
drug-herb interactions. Warfarin is given to thin the blood, thus
preventing the likelihood of clots blocking blood vessels in the
heart, lungs, or brain. Warfarin's dosage needs to be quite exact to
work, so we don't want any herbs affecting it. Herbs and herbal
formulas that contain blood movers must be avoided. This includes,
among others, herbs dan shen (salvia), dang gui (angelica), and yan hu
suo (corydalis), and herb formulas like xue fu zhu yu tang, di dan
tang, and tao he cheng qi tang. Feverfew, garlic, Ginkgo, ginger, and
ginseng may alter bleeding time, and so they also should be avoided by
patients on warfarin.”

General Rules for Taking Herbs, Vitamins and Drugs:

“Don't take herbs that are supposed to do the same thing as a drug
you're on. For example, don't take blood movers like dan shen or dang
gui with warfarin.”



Brand Name: Coumadin
Generic Name: Warfarin 
Drug Class: Anticoagulant 

“This medicine interferes with clotting factors by blocking the action
of vitamin K. This will prevent clots from forming.”

“Do NOT take aspirin without discussing it with your doctor.”

Foods that may change the effects of this medicine are those high in
vitamin K such as; liver, lettuce, broccoli, kale, collard greens,
cabbage, and spinach.

Do not use Warfarin in you are pregnant


“Do not take aspirin or nonsteroidal anti-inflammatory drugs (NSAIDs)
such as ibuprofen (Motrin, Advil, Nuprin, others), ketoprofen (Orudis,
Orudis KT, Oruvail), naproxen (Naprosyn, Aleve, Anaprox), and others
while taking warfarin, except under the direction of your doctor.
These medicines increase the risk of bleeding.”

“Avoid sudden changes in your diet. Vitamin K decreases the effects of
warfarin. Large amounts of vitamin K are found in foods such as liver,
broccoli, brussels sprouts, and green leafy vegetables (e.g., spinach,
Swiss chard, coriander, collards, cabbage). Do not change the amount
of these foods in your diet without first talking to your doctor.”
Do not take warfarin if you:

-  recently had surgery; 
-  have a stomach ulcer or bleeding in the stomach; 
-  have had a certain type of stroke caused by bleeding in the brain;
-  have had an aneurysm; 
-  recently had a spinal puncture or lumbar block anesthesia; or 
-  have bacterial endocarditis (infection of the heart), pericarditis
(swelling of tissue around the heart), or pericardial effusion
(build-up of fluid around the heart).

Web MD


Ginseng with Warfarin (can lead to bleeding)


Warfarin-Food Interactions

“Warfarin causes anticoagulation by antagonizing vitamin K, so dietary
fluctuations in vitamin K content can dramatically influence
anticoagulant control. Phylloquinone, the main dietary source of
vitamin K1, is found mainly in green leafy vegetables, certain
legumes, and canola (rapeseed) and soybean oils. Vitamin K2
(menaquinones) is found principally in animal livers and fermented
foods such as cheese. Uncontrolled bleeding has occurred in
anticoagulated patients as a result of excessive dietary intake of
foods containing both phylloquinones and menaquinones. Other foods
with an anticoagulant effect include garlic, avocado, brussels sprouts
and raw onion. Although salicylates are usually found in medications,
they occur naturally in certain foods and may interfere with

The American Academy of Family Physicians

Herbs with Drug Interactions

Bilberry Vaccinium myrtillus
“Possible Contraindications: Very high doses should be used cautiously
in patients with haemorrhagic disorders and in those taking warfarin.”

Dong Quai Angelica sinensis
“Possible Contraindications: Containdicated in bleeding or very heavy
menstruation, first trimester of pregnancy, acute viral infections
such as colds or influenza.

Feverfew Tanacetum parthenium
“Possible Contraindications: Inhibits iron absorption; Augments the
anticoagulant effect, thus altering clotting or bleeding times.”

Garlic Allium sativum
“Possible Contraindications: HM suggests that substantial amounts of
garlic should not be consumed prior to surgery. May increase the risk
of postoperative bleeding”

Ginger Zingiber officinale
“Possible Contraindications: Caution indicated with patients taking
blood-thinning drugs such as warfarin, or aspirin or who have
increased risk of haemorrhage.”

Ginko Ginko biloba
“Possible Contraindications: Augments the anticoagulant effect, thus
altering clotting or bleeding times.”

“Possible Contraindications: alters bleeding or clotting times.”

Kava Kava Piper methysticum
“Possible Contraindications: may interact with antiplatelet drugs or
anticoagulants (e.g., warfarin, heparin) however there are no case
reports of such interactions.”

Korean Ginseng Panax ginseng
“Possible Contraindications: May interact with monoamine oxidase
inhibitor phenelzine and also with warfarin.”

Pau D'Arco Tabebuia avellanedae
“Possible Contraindications: Patients on anticoagulant therapy should
not be prescribed Pau D’Arco due to the warfarin-like action of
naphthoquinones at high doses. Contraindicated with anticoagulants.
Adverse effects are not expected when consumed with the recommended


All of the medications listed on this page interact with warfarin.




From the National Library of Medicine: 

“Warfarin's anticoagulant effect was potentiated by 6 antibiotics
(cotrimoxazole, erythromycin, fluconazole, isoniazid, metronidazole,
and miconazole); 5 cardiac drugs (amiodarone, clofibrate, propafenone,
propranolol, and sulfinpyrazone); phenylbutazone; piroxicam; alcohol
(only with concomitant liver disease); cimetidine; and omeprazole.
Three patients had a hemorrhage at the time of a potentiating
interaction (caused by alcohol, isoniazid, and phenylbutazone).

Warfarin's anticoagulant effect was inhibited by 3 antibiotics
(griseofulvin, rifampin, and nafcillin); 3 drugs active on the central
nervous system (barbiturates, carbamazepine, and chlordiazepoxide);
cholestyramine; sucralfate; foods high in vitamin K; and large amounts
of avocado.
National Library of Medicine


Here are additional  journal articles from the Nacional Library of
Medcine related to Warafin


From the Bristol-Myers Squibb Company:

“Hepatic Dysfunction: Hepatic dysfunction can potentiate the response
to warfarin through impaired synthesis of clotting factors and
decreased metabolism of warfarin.”

“Caution should be observed when COUMADIN is administered in any
situation or in the presence of any predisposing condition where added
risk of hemorrhage, necrosis, and/or gangrene is present.”

The following factors, alone or in combination, may be responsible for


blood dyscrasias —
collagen vascular disease
congestive heart failure
elevated temperature
hepatic disorders
infectious hepatitis
poor nutritional state
vitamin K deficiency

Specific botanicals reported to affect COUMADIN therapy include the

- Bromelains, danshen, dong quai (Angelica sinensis), garlic, Ginkgo
biloba, and ginseng are associated most often with an INCREASE in the
effects of COUMADIN.

- Coenzyme Q10 (ubidecarenone) and St. John’s wort are associated most
often with a DECREASE in the effects of COUMADIN.

“Special Risk Patients: Caution should be observed when warfarin
sodium is administered to certain patients such as the elderly or
debilitated or when administered in any situation or physical
condition where added risk of hemorrhage is present.”

Bristol-Myers Squibb Company

You must have Adobe Acrobat installed on your computer to be able to
print or read the above publication.
Adobe Acrobat can be downloaded for free.   
The Adobe Website


Patients with congestive heart failure may exhibit greater than
expected PT/INR response to warfarin sodium, thereby requiring more
frequent laboratory monitoring, and reduced doses of warfarin sodium.



Massachusetts General Hospital

“Contraindications for chronic anticoaglation with warfarin include
bacterial endocarditis, mycotic aneurysm, high risk of systemic
hemorrhage or active, uncontrollable bleeding, uncontrolled
hypertension, cerebral amyloid angiopathy, intracerebral hemorrhage,
high risk for traumatic injury due to dysequilibrium, high risk for
excessive or unpredicatble anticoagulation due to alcoholism,
substance abuse, dementia, non-compliance with dosing or dose


Reasons not to take this medicine:
- If you have an allergy to warfarin or any other part of the
- If you are pregnant. 
-If you have any of the following conditions: Bleeding disorder;
hemophilia; thrombocytopenia purpura; leukemia; recent surgery of the
eye or brain; major regional lumbar block anesthesia; surgery
resulting in large, open surfaces.
If you also have any of these conditions: Bleeding; aneurysm;
malnutrition; polyarthritis; diverticulitis; bleeding into the brain;
severe high blood pressure; severe liver disease; pericarditis;
endocarditis; visceral cancer; history of warfarin-induced necrosis.
- If you are a heavy alcohol drinker or binge drinker.


The Merck Manual provides the following information:

Acute Viral Hepatitis
Contributor: Jerome B. Simon, MD

“Acute viral hepatitis is inflammation of the liver caused by
infection with one of the five hepatitis viruses; for most people, the
inflammation begins suddenly and lasts only a few weeks. ..A doctor
may need to discontinue or reduce the dosage of certain drugs that
could build to harmful levels in the body (for example warfarin or
theophylline) because of the liver's inability to process (metabolize)
The Merck Manual

“Using both aspirin and anticoagulants (such as warfarin) could lead
to life-threatening bleeding.”

“Ibuprofen, ketoprofen, and naproxen generally don't impair blood
clotting as much as aspirin does, people shouldn't combine these drugs
with anticoagulants such as warfarin (Coumadin) except under close
medical supervision.”
The Merck Manual


“Vitamin E has very low toxicity at intakes < 800 IU, but vitamin E
can affect coagulation in patients taking warfarin. Daily supplemental
doses > 800 IU generally are not recommended.”
The Merck Manual

“Because most clotting factors are produced in the liver, severe liver
damage can cause a shortage of these factors in the blood. Vitamin K,
found in green leafy vegetables, is necessary for production of the
active forms of several clotting factors. Therefore, nutritional
deficiencies or drugs that interfere with the normal function of
vitamin K, such as warfarin, can cause bleeding.”
The Merck Manual

“Many drugs, both prescription and nonprescription (OTC), can affect
the anticoagulant action of Coumadin. Some medications can enhance the
action of Coumadin and cause excessive blood thinning and
life-threatening bleeding. A few examples of such medications include
Aspirin, Tylenol, alcohol, ibuprofen (Motrin), cimetidine (Tagamet)”
The Merck Manual

======================================== contains about 200 pages of  information on warfarin
including its history, reasons for use, safety, dangers, frequently
asked questions and interactions. Medical literature citations have
been included on most pages to assist in evaluating the information


Search Criteria:

Drug Herb Interactions WARFARIN
Dangerous interactions with warfarin
warfarin and viral liver infections

I hope this helps. Please keep in mind that this information is
general information, and is not intended to be a substitute for
informed professional medical advice.

Best Regards,
omnitemm-ga rated this answer:5 out of 5 stars
good work

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