Choosing the best blood thinner drug for you

Last updated: October 2009

A newly approved drug thins the blood faster, more consistently, and more powerfully than the standard drug, which can fail to prevent deadly blood clots in patients after they undergo a common procedure to avoid or treat a heart attack. But the new drug, prasugrel (Effient), is also more likely to cause potentially fatal bleeding.

Overall, prasugrel may be superior to the approved dose of the older drug, clopidogrel (Plavix), in many cases. But more doctors have been using an initial, higher-than-standard dose of clopidogrel to boost its efficacy, and how that regimen stacks up against prasugrel on key clinical outcomes is unclear. Deciding who is likely to be helped—or harmed—by the various options requires careful consideration of many factors.

Acute coronary syndrome—either unstable angina (escalating heart-related chest pain) or a heart attack in progress—is often treated by percutaneous coronary intervention (PCI), or angioplasty, in which cardiologists inflate a tiny balloon inside a blocked artery. When inflated, the obstruction is pushed against the artery wall, the passageway widens, and blood flows freely. To help prevent blood clots that can block the artery again after the procedure, doctors prescribe medication that inhibits the action of platelets, or clot-forming blood cells.

The body converts prasugrel to its active form considerably faster than it does clopidogrel. Indeed, the approved, 300-mg dose of clopidogrel takes hours to reach full strength—a potentially significant drawback during a coronary crisis. Moreover clopidogrel, at least at the lower dose, doesn't work adequately in a significant minority of patients who may be genetically resistant to the medication.

But there is a hitch: antiplatelet blood thinners increase the chance of hemorrhages—and prasugrel seems to raise that risk more than the approved dose of clopidogrel. Indeed, the package insert for prasugrel contains a black-box warning, the strongest kind, about this bleeding risk, which is sometimes fatal.

The Food and Drug Administration based its approval of prasugrel largely on a 13,608-patient, multicenter clinical trial that compared it with the approved dose of clopidogrel for acute coronary syndrome patients scheduled for PCI; they all received aspirin as well. During the next six to 15 months, the advantages of prasugrel generally outweighed its risks. For every 1,000 patients treated, it prevented 24 more heart attacks, strokes, and cardiovascular deaths than clopidogrel did, while it caused only 10 more cases of serious or fatal bleeding.

Prasugrel was particularly beneficial for people with diabetes. But the risk of bleeding exceeded the benefits in those with a history of strokes or transient ischemic attacks (fleeting, strokelike symptoms). It had no advantage over clopidogrel in two other groups with increased bleeding risk: people older than age 75 or weighing less than about 130 pounds. And those who needed coronary artery bypass surgery after the PCI had substantially higher risks with prasugrel than with the older drug.

But that study leaves at least one major question unanswered: How does prasugrel compare with a larger, 600-mg dose of clopidogrel? The American College of Cardiology and the American Heart Association now recommend it as the generally preferred option before or when PCI is performed. And results of a recent clinical trial suggest that this doubled dose may be generally superior to the approved dose. (Doctors can legally prescribe unapproved but reasonable doses and uses of any approved medication.)

One study found that prasugrel may inhibit platelet activity more than even the doubled clopidogrel dose; experts say that resistance will occur with even higher clopidogrel doses in some patients. But whether that potential advantage translates into fewer blood clots, heart attacks, and strokes remains unknown. Which regimen causes less bleeding has also not been determined.

Potential prasugrel users should know about another research observation: After four months, prasugrel users seemed to experience an increased risk of cancerous tumors than clopidogrel users. That may have occurred either by chance or because higher bleeding rates lead to more scrutiny and detection of cancer. The FDA did not include cancer among the risks listed in the package insert, though it briefly mentioned the possibility elsewhere. But it did order the manufacturer to continue work on another clinical trial, already under way, to assess the drug's cancer-causing potential.

Prasugrel vs. clopidogrel: Making the decision

While further study is clearly needed, some general guidelines can be offered based on what's currently known.

Best candidates.  Prasugrel plus aspirin may be a sensible choice for coronary syndrome patients who are undergoing PCI, have no risk factors for bleeding, and get to the hospital early enough for doctors to determine whether they might need bypass surgery instead.

In contrast, patients with a history of strokes or transient ischemic attacks should avoid prasugrel. (Studies so far have not linked clopidogrel, at least at the approved dose, with increased risks for those patients.) People age 75 or older should probably stick with clopidogrel in most cases, particularly since prasugrel is not recommended for use among this population. For patients who weigh less than about 130 pounds, the package insert says that doctors could consider halving the maintenance dose of prasugrel; although, there is no direct evidence that this smaller dose is actually safer or as effective.

People with active bleeding should avoid both drugs. Those who need bypass surgery should not take prasugrel or, if they've already started, should stop taking it at least a week before their operation. (Clopidogrel should generally be stopped five to seven days before surgery.)

Individualizing the choice.  Despite those general guidelines, doctors should choose the drug regimen based on each patient's particular risk of hemorrhages and blood clots. An increased hemorrhage risk from prasugrel seems to make clopidogrel more desirable, while the high risk of clotting favors prasugrel or the doubled dose of clopidogrel. Some factors that may increase the likelihood or consequences of bleeding, in addition to those listed above, include a history of excessive bleeding (for example, from dental procedures or other minor trauma), stomach ulcers, colon abnormalities, anemia, severe liver disease, and the use of other blood thinners, including nonsteroidal anti-inflammatory drugs such as aspirin, ibuprofen (Advil, Motrin and generics), and naproxen (Aleve and generics). Factors that may make clots more likely include previous clotting problems, heart disease, diabetes, small blood vessels, and the placement of multiple stents, the tiny metallic mesh tubes that prop open PCI-treated vessels.

In general, Consumer Reports medical consultants recommend against using prasugrel for unapproved uses, such as for the prevention of a second heart attack. But they say that off-label use of the drug might be considered for patients who experience a serious blood clot, heart attack, or stroke despite taking clopidogrel. That would be particularly reasonable if doctors can test for platelet responsiveness to clopidogrel.

Choosing a blood-thinning drug: What you can do

A heart attack is a medical emergency, and the decision about which drug to take can be complex, so you may have no say in which medication you take, at least at first. But there are several things you can do if time permits—as often happens with unstable angina—or even after you've started taking a drug:

  • Give your cardiologist all relevant details about your medical history, particularly the bleeding or clotting risk factors listed above as well as any drugs, vitamins, or herbs you're currently taking, especially blood thinners.
  • If your doctor recommends prasugrel even though you have risk factors for bleeding, ask for a thorough explanation and, if possible, seek a second opinion if you're not satisfied. Do the same if he or she recommends an off-label use of prasugrel.

If you're already using prasugrel or clopidogrel, take these precautions:

  • Call your doctor immediately if you notice any signs of excessive bleeding that can't be explained: severe, prolonged, or unusual bleeding; pink or brown urine; red or black stools; bruises or purple skin spots; and coughing up or vomiting blood or clots. But don't stop taking the medication without your doctor's OK.
  • Tell every doctor or dentist you see that you're taking the drug, especially if you're about to undergo an invasive procedure.
  • Use an electric razor or be extra careful when shaving.
  • Take prasugrel with particular caution if you're of Korean descent, because some research suggests that the drug may have a stronger effect.
  • If you're taking clopidogrel or a smaller than recommended dose of prasugrel, consider asking your doctor if you should be tested for adequate platelet inhibition.

This drug safety alert is made possible through a partnership between Consumer Reports Best Buy Drugs and the Research on Adverse Drug Events and Reports (RADAR) group, a pharmacovigilance group led by Charles Bennett, M.D. Ph.D. M.P.P. This is the fifth in a series of reports based on research by the RADAR group.

These materials are made possible by a grant from the state Attorney General Consumer and Prescriber Education Grant Program, which is funded by the multi-state settlement of consumer-fraud claims regarding the marketing of the prescription drug Neurontin (gabapentin).

If you think you have experienced an adverse event with this drug or any drug, especially if it is of a serious nature, it is important to 1) tell your doctor immediately and 2) report the event to the Food and Drug Administration via the FDA's MedWatch Web site at or by calling 1-800-FDA-1088.

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