Coagulation Counseling

APRIL 01, 2009
Anna D. Garrett, PharmD, BCPS, CPP

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 demonstrated that clopidogrel is less effective in patients who have had a myocardial infarction (MI), are younger than 45 years of age, and have a certain genetic variation in the cytochrome P (CYP) 450 isoenzyme CYP2C19. In addition, researchers found that these younger patients with the genetic variation were much more likely to die, have another MI, and require urgent repeat coronary intervention or have stent thrombosis.

Between 1996 and 2008, 259 patients who survived a first MI and were exposed to clopidogrel treatment for at least 1 month had their genetic status with respect to the above gene investigated. Of the patients, 73 (28%) were carriers of the gene variation, and 186 were noncarriers. Median clopidogrel exposure was just over a year, and patients were then followed up every 6 months.

When looked at alone, thrombosis was 6 times more likely to occur in patients with the variation. The detrimental effect of the variation also persisted from the initiation of clopidogrel treatment until the end of follow-up, up to 8 years later.

VTE Risk Low with Air Travel

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

The rate of VTE in 1 study of 9000 business travelers over 4.5 years was 1 case for every 4500 flights. Although studies overall do show an association between VTE and long-haul flights— with risks of up to 4-fold—results vary depending on the study methods. One systematic review calculated a pooled odds ratio of 1.59 for VTE from casecontrol studies and a relative risk of 2.93 from several prospective controlled cohort studies.

The greatest risk factor for development of VTE is immobility, according to the authors. Other risk factors that are known to increase the risk of VTE associated with flying include obesity, recent surgery, use of oral contraceptives— which increased the risk 16-fold in 1 study—and the presence of factor V Leiden, which increased the risk 14-fold.

Recommendations to reduce the risk of developing VTE during air travel include:

  • 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 stockings with an ankle pressure of 17 to 30 mm Hg also can reduce risk, and the researchers recommend use of compression stockings in individuals prone to immobility.

Currently no clear recommendations have been issued on the use of any pharmacologic agents to prevent VTE during air travel.

ATryn Approved for Postsurgical Clot Prevention

The FDA has approved GTC Biotherapeutics and Lundbeck Inc’s ATryn (antithrombin recombinant) for the prevention of perioperative and peripartum thromboembolic events in hereditary antithrombin-deficient patients.

The prevalence of hereditary antithrombin deficiency in the general population is approximately 1 in 2000 to 1 in 5000. Half of these patients may experience a thrombosis before age 25, and up to 85% may suffer a thromboembolic event by age 50, according to 1 study.

People with hereditary antithrombin deficiency are at increased risk for venous thromboembolic events, including pulmonary embolism and deep vein thrombosis.

The safety and efficacy of ATryn was established in clinical studies conducted in hereditary antithrombin-deficient patients with a history of thromboembolic events. During these studies, ATryn was shown to prevent the formation of clinically overt thromboembolic events. Postmarketing studies will be performed to assess safety and immunogenicity after repeat dosing.

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