Losartan (Cozaar), which is used to treat high blood pressure, is metabolized by liver enzymes CYP2C9 and CYP3A4 to an active metabolite, E-3174, which has greater antihypertensive activity than Losartan itself.

We also know that soy extract activates CYP2C9 and CYP3A4 in the lab. Should we worry about a soy-drug interaction?

First, the details.

  • 18 healthy Chinese women were given losartan 50 mg, with and without soy extract.
  • Blood levels of losartan and E-3174 were measured for 12 and 24 hours, respectively.
  • Then, starting on the 8th day and continuing through day 21, each woman consumed 2, 1000-mg Genistein Soy Complex tablets after meals, twice daily, for 14 days.
  • On day 22, all volunteers received losartan 50 mg, and blood samples were collected again.

And, the results.

  • Soy extract had no significant effect on the metabolism of losartan or E-3174.

The bottom line?
The researchers concluded, “A significant interaction between soy extract and losartan is unlikely to occur in females.”

Others have found that even though soy extract can activate CYP3A4 in the laboratory, there’s no correlation to any effects when humans take it.

5/21/09 10:10 JR

Hi, I’m JR

John Russo, Jr., PharmD, is president of The MedCom Resource, Inc. Previously, he was senior vice president of medical communications at www.Vicus.com, a complementary and alternative medicine website.