[Aerodiol: the efficacy and tolerability of intranasal estrogen administration. An overview]

Estrogen supplementation, given mainly by oral or transdermal route has been shown to decrease climacteric symptoms, bone turnover, prevent postmenopausal bone loss, and significantly reduce fracture risk in both early and late postmenopausal women. Estrogens exert their principal biological effects through the actions on 2 different intracellular estrogen receptor (ER) proteins, ERa and ERb. These receptors, are completely distinct in their action. However, regardless the type of receptor involved, the response induced through the action of ER induction can be dependent also on the total dose exposure rather than estradiol concentrations at subsaturating levels. The nasal route is an effective and well-established route of drug delivery. Nasal administration produces a pulsed profile of plasma estradiol, with plasma levels rising rapidly and returning to pre-administration levels within 12 h (fall to 10% of their peak level within approximately 2 h). As a consequence, daily intranasal administration results in a pulse-like estrogen profile, rather than the relatively sustained serum levels attained with both oral and transdermal administration. In addition, exposure obtained with a single dose is compared with the exposure obtained with the same total dose given as 2 divided doses administered 12 h apart. It's known that different route of administration exert different biological and clinical

In the years, several clinical studies have demonstrated the efficacy and safety of intranasal estradiol in the treatment of climacteric symptoms, compared with other routes of estrogen administration. Interestingly, intranasal therapy also showed a lower tendency to stimulate endometrial proliferation than the oral route, with a high incidence of atrophic endometrium maintained during the long-term study. The reduced level of stimulation of the reproductive organs produced by Aerodiol compared with oral estradiol therapy of equivalent efficacy on climacteric symptoms may be related to the pulsed kinetic profile of estradiol exposure that occurs with the intranasal route. Improvement of climacteric symptoms observed with nasal estradiol administration is comparable to that seen with transdermal or oral estrogens. A similar reduction in Kupperman Index or in the number of hot flushes was reported over a 6-month period with results similar to those of several studies performed with transdermal patches delivering estradiol or with conjugated equine estrogen. Different routes of administration may exert different results in terms of compliance, biological and clinical effects even if long term clinical trials are needed for demonstrating it. The pulsed kinetics of Aerodiol may exert less side effects in terms of coagulation cascade activation and a favourable lipid profile with less mammary tissue stimulation. These aspects became of paramount importance since the recent publication of 2 trials, Women Health Initiative (WHI) and Heart and Estrogen/Progestin Replacement Study (HERS), regardless their important population selection bias and uncertain results, left important consequences in terms of HRT indication and use for both women and clinicians. In conclusion, Aerodiol introduces the new concept of pulsed estrogen therapy. Pulsed estrogen therapy is safe, well accepted and highly efficient in alleviating postmenopausal symptoms and prevent postmenopausal bone loss. Aerodiol therapy demonstrated also a lower stimulation of reproductive tissues (endometrium, breast) compared with the equivalent oral therapy, with important repercussion for future HRT strategies.