About warfarin

Warfarin reduces the blood’s ability to clot (coagulate) and prevents blood clots from forming in the arteries and veins. It is prescribed to people who have a history of abnormal blood clots or who are at high risk of having abnormal clots.

Warfarin is a drug of considerable benefit after heart-valve replacement and in the prevention of blood clots from a type of heart-rhythm disturbance known as atrial fibrillation. It also reduces the risk of death, recurrent heart attacks and stroke after a heart attack.

Patients over 60 years of age should generally be taking less than the usual adult dose to lower the risk of heavy bleeding (hemorrhage). After a patient has taken warfarin for three months, a doctor should reevaluate the patient’s need to continue taking it.

Who should not use warfarin

Do not use warfarin if you have or have had eclampsia or preeclampsia; blood disorders; or severe, uncontrolled high blood pressure. You should not use warfarin if you have or have had recent surgery, an aneurysm or dissecting aorta, a threatened or incomplete abortion, confirmed or suspected cerebrovascular hemorrhage or active bleeding.

Before you use warfarin

Tell your doctor about any other drugs you take (including aspirin, herbs, vitamins and other nonprescription products) and whether you have or have had:

• allergies to drugs
• heart problems (including atrial fibrillation, myocardial infarction or stroke)
• thromboembolism
• severe allergies
• ulcers or other lesions of the gastrointestinal tract, respiratory tract or urinary tract
• kidney or liver problems
• diverticulitis
• vasculitis
• infectious disease
• vitamin K deficiency
• alcohol dependence
• severe inflammation of blood vessels
• subacute bacterial endocarditis (infection of the heart)
• diabetes
• recent injury
• childbirth
• spinal puncture
• a fall or blow to the body or head
• wounds from trauma, ulcers or surgery
• fever lasting more than a couple of days
• an intrauterine device (IUD)
• heavy or unusual menstrual bleeding
• medical or dental surgery
• severe or continuing diarrhea

How to take warfarin

It is very important that you take warfarin exactly on schedule, since failing to take this drug properly can cause serious adverse effects (see “Side effects” below). While taking warfarin, patients should be monitored with regular blood tests to ensure that the most effective dose of the drug is being taken.

If you miss a dose, take it as soon as you remember, but skip it if you don’t remember until the next day. Do not take double doses. Keep a record of missed doses and give the list to your doctor at each visit.

Do not share your medication with others.

Take the drug at the same time(s) each day.

Store at room temperature with lid on tightly. Do not store in the bathroom. Do not expose to heat, moisture or strong light. Keep out of reach of children.

Side effects

Call your doctor immediately if you experience: abnormal bleeding; bloody, cloudy or dark urine; difficult or painful urination or sudden decrease in the amount of urine; dizziness or fainting; swelling of the ankles, feet or legs; unusual weight gain; blue or purple toes; chills, fever, sore throat or unusual tiredness; yellow eyes or skin; nausea or vomiting; diarrhea; skin rash, hives or itching; sores or white spots in mouth or throat; sores on skin; stomach cramps or pain; loss of appetite; nervousness; confusion; blurred vision; chest pain; or difficulty breathing.

Call your doctor if these symptoms continue: bloated stomach or gas, cold intolerance, diarrhea, lossof appetite, nausea or vomiting,stomach cramps or pain.

Skin necrosis. Australia’s Adverse Drug Reactions Advisory Committee (ADRAC) has received nine reports of death of skin tissue (skin necrosis) with warfarin use, of which three were fatal. In four cases, the onset occurred within seven days of commencing warfarin, but in three cases, the first symptoms occurred three to eight weeks after starting warfarin.

Risk of tendinitis when used with fluoroquinolone antibiotics. In 2006, we petitioned the Food and Drug Administration (FDA) to add a warning to the product label of all fluoroquinolone antibiotics to alert doctors to the risk of tendinitis, including a warning of the possibility of complete tendon rupture, which can occur when fluoroquinolones are used with warfarin. The class of fluoroquinolone antibiotics includes drugs such as ciprofloxacin (CIPRO). The onset of symptoms is sudden and has occurred as soon as 24 hours after starting treatment with a fluoroquinolone. Most people have recovered completely after one to two months.

Signs of overdose

If you suspect an overdose (see the signs below), call (800) 222-1222 to contact your poison control center:

• bleeding gums when brushing teeth
• nosebleeds
• unexplained bruising
• unusually heavy bleeding from cuts or wounds
• unusually heavy or unexpected menstrual bleeding
• abdominal pain or swelling
• sudden light-headedness
• weakness
• loss of consciousness
• backaches
• blood in urine
• bloody or tarry stools
• constipation
• headache
• joint pain
• stiffness or swelling
• blood or material that looks like coffee grounds expelled when coughing or vomiting
• pinpoint red spots on skin

Interactions 

Warfarin can interact with nearly all drugs and some dietary supplements. Its anti-clotting action is very difficult to control when other drugs are added or subtracted, or when another drug’s dose is changed. Another medication may either increase or decrease warfarin’s action (see “Warfarin: Interactions” box below). 

If you are taking warfarin, you should notify your doctor before taking any product containing acetaminophen. Acetaminophen may interact with warfarin to increase the risk of bleeding, a risk that rises with increasing doses of acetaminophen.

This risk has been found to increase tenfold in people taking 28 or more regular-strength acetaminophen tablets per week, or the equivalent of 18 or more extra-strength tablets per week, compared to those taking warfarin and no acetaminophen. A regular-strength acetaminophen tablet contains 325 milligrams (mg) of acetaminophen, and an extra-strength tablet contains 500 mg of the drug. Results published from a prospective randomized, parallel, double-blind, placebo-controlled study of 45 patients found that acetaminophen (at a dose of 2 or 3 grams a day, administered for 10 days) increased the anticoagulant effect of warfarin in stable patients.

The U.K. Medicines and Healthcare products Regulatory Agency (MHRA) has received seven reports suggesting an interaction between warfarin and the dietary supplement glucosamine, according to the MHRA and the U.K. Committee on Safety of Medicines. In those cases, patients who previously had a stable international normalized ratio (INR, which is a measurement of how properly one’s blood clots) while receiving warfarin experienced an INR increase (potentially dangerous abnormal thinning of the blood) after they started receiving glucosamine supplements. ADRAC reported in February 2008 that it had received 10 reports of an increase in INR values associated with warfarin and glucosamine use.

When using warfarin

Wear a medical identification bracelet or carry a card stating that you take warfarin.

Be very careful doing activities that may cause cuts or bleeding (such as shaving or cooking).

Consult with your doctor immediately if any signs of bleeding occur.

Do not drink alcohol. Eat a normal, balanced diet. Do not change your diet or take nutritional supplements or vitamins without first checking with your doctor.

If you plan to have any surgery, including dental, tell your doctor that you take this drug.

Do not take any other drugs, including nonprescription products (aspirin, cold remedies, antacids, laxatives), or change the dose of drugs you are taking without consulting your doctor.

Be sure to schedule regular doctor visits for blood tests. Ask your doctor which of these tests should be done periodically while you are taking this drug:

• prothrombin time, now measured by the INR (INR should be checked daily for the first week, weekly until a therapeutic level is achieved and then monthly)
• complete blood count
• stool tests for possible blood loss
• urine tests for possible blood loss

Pregnancy and breast-feeding warnings

You should not take warfarin while nursing. Warfarin should not be used if you are pregnant or are thinking of becoming pregnant. Severe malformations have occurred in infants of mothers taking this drug.

Regulatory actions surrounding warfarin

2006: The FDA announced on Oct. 10 that it would require that an agency-approved Medication Guide, which provides information about drug safety, accompany all new and refill prescriptions for the blood thinner warfarin.
Warfarin is one of a limited number of drugs for which the FDA requires an FDA-approved Medication Guide to be dispensed when the prescription is filled. An FDA advisory committee has unanimously recommended that all drugs be accompanied by such medication guides, but at present, less than 5 percent of drugs are. The other 95 percent of drugs are accompanied by unregulated, often dangerously incomplete, information leaflets not approved by the FDA.

2010: In January, the FDA issued information on the dosage and administration of warfarin. The advisory emphasized that the dose of warfarin must be individualized and that lab monitoring is necessary. The appropriate dose of warfarin is influenced by various factors, stated in the advisory, and not all of the factors leading to the variability in warfarin dose are known.

Clopidogrel
(Family: adenosine diphosphate blockers, blood-clotting inhibitors)

Limited Use: offers limited benefit or benefits certain people or conditions

About clopidogrel

Clopidogrel is approved by the FDA to reduce the risk of a new heart attack or stroke in patients with a history of a recent heart attack or stroke. The drug has also been approved by the FDA for a condition known as acute coronary syndrome in patients who may be treated with medicines, with a stent (a metal device placed in a coronary vessel to keep it open) or with bypass surgery to reduce the rate of heart attack, stroke and cardiovascular death. Acute coronary syndrome consists of unstable chest pain (angina) and changes in the electrocardiogram (EKG or ECG) that suggest a heart attack.

Because the retail cost of clopidogrel is at least 100 times greater than the cost of aspirin and is no better than aspirin in preventing a second heart attack or stroke, its use should be limited to those who cannot take aspirin. The long-term use of clopidogrel in the management of patients with acute coronary syndromes is unclear. Long-term clopidogrel may be no better than aspirin.

Who should not use clopidogrel

Do not use if you have or have had an intracranial hemorrhage or a peptic ulcer.

Before you use clopidogrel

Tell your doctor if you have or have had an allergy to this drug, bleeding problems, liver disease, stomach ulcers, recent surgery or trauma. Also tell your doctor if you are pregnant or breast-feeding and if you are taking any other drugs, including aspirin, herbs, vitamins and other nonprescription products.

How to take clopidogrel

If you miss a dose, take it as soon as you remember, but skip it if it is almost time for the next dose. Do not take double doses.

Do not share your medication with others.

Take the drug at the same time(s) each day.

Store at room temperature with the lid on tightly. Do not store in the bathroom. Do not expose to heat, moisture or strong light. Keep out of reach of children.

Side effects

Call your doctor immediately if you experience: black, tarry stools; blood in urine or stools; chest pain; coughing; fainting; fever, chills, sneezing or sore throat; frequent, painful or difficult urination; generalized pain; sudden or severe headaches; irregular heartbeat; joint pain; nosebleeds; red or purple spots on the skin; runny nose; shortness of breath; skin blistering, flaking or peeling; severe stomach pain; swelling of the feet or lower legs; ulcers, sores or white spots in the mouth; unusual bleeding or bruising; vomiting of blood or material that looks like coffee grounds; or sudden weakness.

Call your doctor if these symptoms continue: abdominal or stomach pain, anxiety, back pain, constipation, diarrhea, depression, dizziness, fever, chills, headache, heartburn, insomnia, itching, joint pain, leg cramps, muscle aches, nausea or vomiting, numbness or tingling or skin rash.

Clopidogrel and the blood disorder thrombotic thrombocytopenic purpura (TTP). TTP is a life-threatening adverse effect that is characterized by a breakdown of red blood cells, low levels of cells that help stop bleeding (platelets), fever, mental changes and kidney problems. Clopidogrel and ticlopidine (TICLID), a close chemical relative of clopidogrel, have been linked to TTP. In the two-year period between March 1998 and March 2000, TTP was identified in 11 patients from an active surveillance program that involved blood banks around the U.S. Between the end of 1997 and the fourth quarter of 2001, the FDA received 16 reports of TTP. (It is not known if these 16 reports included the 11 previously mentioned.)

Clopidogrel in research studies

Cardiovascular events. Researchers have struggled to show that clopidogrel is better than aspirin in preventing certain cardiovascular incidents such as heart attack and stroke, and they have been largely unsuccessful in doing this.

A single clinical trial was the basis for the FDA approval of clopidogrel for preventing a second heart attack or stroke. In this trial, clopidogrel was directly compared to aspirin. The difference between clopidogrel and aspirin was very small but statistically significant, favoring clopidogrel. A critique of the trial concluded by saying that the result “leaves open questions about whether such a difference is clinically meaningful or, in fact, reproducible.”

The trial did not show clopidogrel to be superior to aspirin in preventing a second heart attack or stroke. The fact that clopidogrel is no better than aspirin in preventing a second heart attack or stroke did not stop its manufacturer from advertising it as a better drug overall. This resulted in the FDA warning Bristol-Myers Squibb/Sanofi in April 2001 about its false and misleading promotion of clopidogrel as being superior to aspirin.

In the August 1999 issue of the journal Stroke, researchers compared the benefits of clopidogrel to aspirin in reducing stroke, heart attack and death from diseases of the blood vessels, concluding that these two drugs work in different ways to prevent platelet aggregation, and currently there is no evidence that one way is better than the other.

Also, an NEJM study published on April 20, 2006, found that clopidogrel, when given in combination with aspirin, was overall no more effective than aspirin alone in reducing the rate of heart attacks, strokes or deaths from cardiovascular causes.

In a study examining the management of acute coronary syndromes, clopidogrel was found to be marginally better than aspirin by only 2.1 percent. However, in statistically significant results, there were more patients with major bleeding episodes (defined as needing a transfusion of at least two units of blood) in those taking clopidogrel. In this study, 1 percent more patients taking clopidogrel had a major bleeding episode compared to the aspirin-treated patients, but there was no statistically significant difference between those taking clopidogrel or aspirin inregard to episodes of life-threatening bleeding.

A further analysis of the trial mentioned immediately above found that in patients with acute coronary syndrome who were taking aspirin, adding clopidogrel was beneficial, compared to a placebo, in reducing major cardiovascular events. However, it has been noted that beyond 30 days, there was no significant advantage to treatment with clopidogrel over a placebo in regard to cardiovascular death or nonfatal heart attack.

Effect decreased when combined with omeprazole (PRILOSEC). A study published in 2008, investigating the effect of the heartburn drug omeprazole (a proton pump inhibitor [PPI]) on the action of clopidogrel plus aspirin therapy, found that omeprazole significantly decreased the effect of clopidogrel, meaning that clopidogrel could then be less effective in preventing strokes and heart attacks. Physicians should be aware of this association, since this drug combination is widely prescribed. Patients also should be made aware of this drug interaction, since omeprazole is available over the counter without a prescription.

In 2009, the FDA issued information concerning the use of clopidogrel and omeprazole. According to the FDA release, the concurrent use of clopidogrel and omeprazole resulted in a reduction in the effectiveness of clopidogrel. The FDA release also stated that separating the administration time of the dose of each drug did not reduce the harmful interaction of this therapy.

According to the FDA, “Other drugs that are expected to have a similar effect and should be avoided in combination with clopidogrel include: cimetidine, fluconazole,
ketoconazole, voriconazole, etravirine, felbamate, fluoxetine, fluvoxamine and ticlopidine.”

Genetic factors. Published medical literature shows that clopidogrel is less effective in some patients than it is in others. This may be due to genetic factors that influence how the body metabolizes clopidogrel or the effect that certain other drugs (such as PPIs) have on the effectiveness of clopidogrel. The FDA is working with the manufacturer to obtain more information on this.

Bleeding ulcers. Research published in the Jan. 20, 2005, NEJM found “an astonishingly high rate of bleeding ulcers” in patients taking clopidogrel compared to patients taking aspirin plus the antiulcer/heartburn drug esomeprazole (NEXIUM). No safety advantage was found for clopidogrel over aspirin plus esomeprazole in ulcer bleeding.

When using clopidogrel

Do not exceed the prescribed dose.
Tell any doctor, dentist, emergency medical technician, pharmacist or surgeon whose care you are under that you take clopidogrel. This is especially important for any surgery, including dental.

Pregnancy and breast-feeding warnings

You should not take clopidogrel while nursing. Clopidogrel should not be used if you are pregnant or are thinking of becoming pregnant. Severe malformations have occurred in infants of mothers taking this drug.

Regulatory actions surrounding clopidogrel

In response to an action letter request by the FDA, the manufacturer of clopidogrel revised the “Precautions” section of the product label to include the following statement: “In patients with recent TIA [transient ischemic attack] or stroke who are at high risk for recurrent ischemic events, the combination of aspirin and PLAVIX has not been shown to be more effective than PLAVIX alone, but the combination has been shown to increase major bleeding.”

2010: In March, the FDA issued an advisory that a boxed warning has been added to the product information for clopidogrel (see "Clopidogrel Interactions box above).