Coagulation Counseling

Dr. Garrett is manager, Outpatient Clinical Pharmacy Programs, at Mission Hospitals in Asheville, North Carolina.

Garlic—Warfarin Risk Overstated?

A retrospective study conducted by researchers in England suggests that taking garlic supplements does not increase the risk of bleeding when combined with warfarin. The study identified patients in primary care practices who were taking the combination and matched them with patients of similar age, sex, and general practice who were not taking garlic. Garlic use was self-reported.

International normalized ratio (INR) results were assessed for the preceding 12 months. The researchers found no evidence to suggest that garlic consumption— either as a supplement or in cooking—is associated with more frequent hemorrhagic complications or less control of INR. Poor INR control was associated with taking larger numbers of prescription medicines, and in particular, during prescription changes.

Garlic is thought to provide several cardiovascular benefits, including lowering of blood pressure, cholesterol, and antithrombotic activity; however, little evidence exists to conclusively support these effects. Concerns about a garlic—warfarin combination arise from reported effects of garlic on platelet aggregation.

The researchers concluded that further research was warranted into whether increased INR monitoring is needed when garlic is used as a supplement. They also stated that these data render clinically significant interactions between warfarin and garlic intake unlikely.

Travel and Risk for Venous Thromboembolism

Various studies over the years have attempted to correlate traveling with venous thromboembolism (VTE), but results often have been conflicting, making concrete conclusions or recommendations difficult. A recent

metaanalysis of 14 studies examined the risk of travel and VTE. The authors attempted to determine whether a dose—response relationship exists and also identify reasons for the contradictory results of previous studies. Reports were included if they investigated the association between travel and VTE for individuals who used any mode of transportation and if nontraveling persons were included for comparison.

Of 1560 identified abstracts, 14 studies (11 case-controls, 2 cohorts, and 1 case-crossover) met inclusion criteria and included 4055 cases of VTE. Compared with nontravelers, the overall pooled relative risk for VTE in travelers was 2.0.

Significant heterogeneity was present because of the method for selecting control participants, which makes conclusions difficult. Some studies used control participants who had been referred for VTE evaluation, and others used nonreferred control participants. When the studies that used referred control participants were excluded, the pooled relative risk for VTE in travelers was 2.8, without a lot of variation in result.

A dose—response relationship was identified, with an 18% higher risk for VTE for each 2-hour increase in duration of travel by any mode and a 26% higher risk for every 2 hours of air travel.

No standard recommendations for prevention of travel-related VTE currently exist. Long-distance travelers are advised to stop occasionally for short walks (car travel), or to perform “foot flexes” and walk around the airplane if possible during air travel.

Lower Leg Superficial Vein Thrombosis May Warrant Closer Look

The results of a recently published study suggest that patients who present with superficial vein thrombosis (SVT) also may have deep vein thrombosis (DVT). The goal of this prospective study was to evaluate the occurrence of DVT in patients with SVT. Forty-six outpatients at the Medical University of Graz in Austria were enrolled. All had been diagnosed with SVT and underwent color-coded duplex sonography of both lower extremities at the beginning of the study.

In 24% of patients, a DVT was found. Most were asymptomatic. In 73% of these patients, the DVT occurred in the affected leg, in 9% in the contralateral leg, and in 18% in both legs. The calf muscle veins were most commonly involved. In all patients with DVT, the SVT was located on the lower leg and the D-dimer findings were positive.

SVT is not a life-threatening disease, but DVT can be. Given these results, the risk of concomitant DVT cannot be ignored.

The authors concluded that colorcoded duplex sonography should be performed in patients with SVT to rule out DVT.