Coagulation Counseling

Dr. Garrett is manager of the Health Education Center at Mission Hospitals in Asheville, North Carolina.

Gene Affects Clopidogrel Efficacy in Younger Patients

A recently published study demonstratedthat clopidogrel is less effectivein patients who have had a myocardialinfarction (MI), are younger than 45years of age, and have a certain geneticvariation in the cytochrome P (CYP)450 isoenzyme CYP2C19. In addition,researchers found that these youngerpatients with the genetic variation weremuch more likely to die, have anotherMI, and require urgent repeat coronaryintervention or have stent thrombosis.

Between 1996 and 2008, 259 patientswho survived a first MI and were exposedto clopidogrel treatment for atleast 1 month had their genetic statuswith respect to the above gene investigated.Of the patients, 73 (28%) werecarriers of the gene variation, and 186were noncarriers. Median clopidogrelexposure was just over a year, andpatients were then followed up every6 months.

When looked at alone, thrombosiswas 6 times more likely to occur inpatients with the variation. The detrimentaleffect of the variation also persistedfrom the initiation of clopidogreltreatment until the end of follow-up, upto 8 years later.

VTE Risk Low with Air Travel

The risk of venous thromboembolism(VTE) associated with air travel is low, anew review on medical issues associatedwith commercial flights concludes.

The rate of VTE in 1 study of 9000business travelers over 4.5 years was1 case for every 4500 flights. Althoughstudies overall do show an associationbetween VTE and long-haul flights—with risks of up to 4-fold—results varydepending on the study methods. Onesystematic review calculated a pooledodds ratio of 1.59 for VTE from casecontrolstudies and a relative risk of2.93 from several prospective controlledcohort studies.

The greatest risk factor for developmentof VTE is immobility, accordingto the authors. Other risk factors thatare known to increase the risk of VTEassociated with flying include obesity,recent surgery, use of oral contraceptives—which increased the risk 16-foldin 1 study—and the presence of factor VLeiden, which increased the risk 14-fold.

Recommendations to reduce the riskof developing VTE during air travelinclude:

• Being well-hydrated
• Reducing alcohol and caffeine consumption
• Changing positions or walking throughout the cabin
• Doing periodic calf-muscle exercises to reduce venous stasis.

Use of graduated compression stockingswith an ankle pressure of 17 to 30mm Hg also can reduce risk, and theresearchers recommend use of compressionstockings in individuals proneto immobility.

Currently no clear recommendationshave been issued on the use of anypharmacologic agents to prevent VTEduring air travel.

ATryn Approved for Postsurgical Clot Prevention

The FDA has approved GTC Biotherapeuticsand Lundbeck Inc’s ATryn (antithrombinrecombinant) for the preventionof perioperative and peripartumthromboembolic events in hereditaryantithrombin-deficient patients.

The prevalence of hereditary antithrombindeficiency in the general populationis approximately 1 in 2000 to1 in 5000. Half of these patients mayexperience a thrombosis before age25, and up to 85% may suffer a thromboembolicevent by age 50, accordingto 1 study.

People with hereditary antithrombindeficiency are at increased risk forvenous thromboembolic events, includingpulmonary embolism and deep veinthrombosis.

The safety and efficacy of ATryn wasestablished in clinical studies conductedin hereditary antithrombin-deficientpatients with a history of thromboembolicevents. During these studies,ATryn was shown to prevent the formationof clinically overt thromboembolicevents. Postmarketing studies will beperformed to assess safety and immunogenicityafter repeat dosing.