Topical estrogen approved for treating hot flashes: lotion for short-term use only.(Gynecology)

The Food and Drug Administration last month approved Estrasorb--the first topical estrogen therapy or treating moderate to severe vasomotor symptoms of menopause.

The novel estrogen-based skin lotion was approved for short-term use only. Women should not apply Estrasorb and sunscreen at the same time because this could affect the amount of estradiol that is absorbed.

Estrasorb uses oil and water nanoemulsions that encapsulate and deliver 17[beta]-estradiol through the skin. The product is the first drug using this new topical emulsion technology to complete a phase III trial and receive FDA approval, according to its manufacturer, Novavax Inc. of Columbia, Md.

Estrasorb is distributed in pouches, each containing 1.74 g of emulsion; women apply 1 pouch to each leg once a day, said Dr. D. Craig Wright, chief scientific officer at Novavax and inventor of the technology.

The emulsion was tested for potential transfer of the active ingredient to male Partners. Studies showed that vigorous rubbing of a man's forearm for 2 minutes across a leg where Estrasorb had been applied resulted in a 25% increase in the man's estradiol levels, but the level remained within the normal range.

Transdermal delivery systems like Estrasorb's have an advantage over oral delivery systems because of the lack of the first-pass hepatic effect, which causes high peaks and troughs in blood levels of the delivered drug. In transdermal systems, drug concentrations rise slowly and remain at the desired level, Dr. Wright said.

With Estrasorb, slow uptake occurs throughout the day; levels peak between 12 and 18 hours and are maintained at between 20 picograms/mL and 80-100 picograms/mL. "The dosing is independent of body mass index," Dr. Wright said.