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Progestin Use, But Not Oestrogen Use, Associated With Higher Risk of Venous Thromboembolic Events: Presented at NAMS

By John Otrompke

SAN DIEGO -- October 4, 2009 -- A study of over 1 million women in the Regione Emilia Romagna health system in Italy found no statistically significant differences in the risk of venous thromboembolism (VTE) between patients who took oral and transdermal oestrogen.

However, a significant association between progestin use and VTE was observed, researchers stated here at the 20th Annual Meeting of the North American Menopause Society (NAMS).

"The largest study to date, the ESTHER study, showed roughly 4 times more VTEs with oral over transdermal oestrogen," said Valerie A. Omicioli, MD, University of Maryland Ob/Gyn Associates, Baltimore, Maryland, on October 1. "We did see a difference -- there was a 69% higher risk with oral oestrogens, but it could have been by chance alone."

To examine the question, Dr. Omicioli and colleagues looked at over 1 million women aged older than 44 years from 2000 to 2001. Cases were defined as women currently using oral or transdermal oestrogen, with or without a progestin, in whom a discharge diagnosis of a venous thromboembolic event was documented.

All data on hormone use were ascertained by documenting a prescription refill within the 6 months preceding the index date. Data were collected from computerised hospital discharge ICD-9 codes and pharmaceutical billing data.

The research was conducted in a nested format, meaning that each case was age-matched with 10 controls who were current oestrogen users who had not had a VTE prior to the case's index date, said Dr. Omicioli. Researchers projected that the study would identify 85 cases of VTE who were users of oestrogen, and 850 matched controls.

Of 68,607 women who had used some form of hormone therapy, 78% had been prescribed transdermal oestrogen.

"Women who took both oestrogen and progestin had a risk of blood clots that was 7.37 times higher than those who took oestrogen alone," Dr. Omicioli said.

The findings are significant, because women with intact uteruses who take oestrogen must also take progestin, or they have a higher risk of uterine cancer, said Dr. Omicioli.

"Oral oestrogen goes from the stomach directly to the liver, in a process known as hepatic first-pass metabolism, meaning that it doesn't go into the bloodstream the first time alone," Dr. Omicioli explained. "In the liver, it induces the synthesis of proteins, some of which promote blood clots. Transdermal oestrogen bypasses the first trip to the liver, because it goes directly from the skin to the blood stream."

The study also found an increased risk for certain other factors, such as cancer, trauma, fractures, coagulopathies, such as protein S or C deficiency, and surgery, which is a well-known risk factor for blood clots because patient are immobilised afterward.

While it was not known why progestin is associated with increased risk for VTE, Dr. Omicioli hoped that publication of 5 years worth of additional data gathered since the initial study may enable confirmation or refutation of the association between VTE and oral oestrogen.

[Presentation title: Comparison of Transdermal and Oral Estrogen Hormone Therapy and Risks of Venous Thromboembolic Events. Abstract P-37]

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