Glenn D. Braunstein, MD

Department of Medicine, Cedars-Sinai Medical Center, Los Angeles, CA, USA

Glenn D. Braunstein, MD, Room 2119, Plaza Level, Cedars-Sinai Medical Center, 8700 Beverly Blvd., Los Angeles, CA 90048, USA. Tel: (+1) 310 423 5140; Fax: (+1) 310 423 0437; E-mail: braunstein@cshs.org.

Abstract

Introduction. A Food and Drug Administration advisory group has questioned the long-term safety of testosterone administration to postmenopausal women. Although only short-term data exist on safety from the double-blind, placebo-controlled trials, testosterone has been used for more than 50 years. Therefore, some data concerning the long-term safety issues must exist in the literature.

Aim. To review the published data concerning the safety of administration of testosterone to women.

Methods. Review of published articles identified by a search of the Ovid databases and bibliographies from articles identified as dealing with the topics of testosterone or androgen treatment of women.

Results. The major adverse reactions to exogenous androgens are the expected androgenic side effects of hirsutism and acne. High-density lipoprotein levels may be decreased with oral androgens. There are insufficient long-term safety data regarding breast, endometrium, or heart safety to draw strong conclusions, although the data available to date are reassuring.

Conclusions. Testosterone administration to postmenopausal women that result in physiological to slightly supra- physiological serum-free testosterone levels is safe for at least 2 years.

Key Words. Breast Cancer; Cardiovascular Disease; Endometrial Cancer; Hirsutism; Menopause; Testosterone

Introduction

A number of well-designed, randomized controlled studies have demonstrated that testosterone administration to postmenopausal women improves libido and sexual function [1,2]. However, anecdotal reports of adverse effects in women receiving pharmacological doses of androgens, or extrapolation from studies in men (whose serum testosterone levels are 10-20 times higher than women), along with the concerns about sex steroid hormone administration raised by the Woman’s Health Initiative and the Heart and Estrogen/ Progestin Replacement Study, have led the U.S. Food and Drug Administration (FDA) to request long-term safety studies oftestosterone before con-sidering approval of such therapy for postmenopausal women with hypoactive sexual desire disorder [3]. Although testosterone and other androgens have been used for this purpose for more than half a century, very limited long-term safety data are available. What information is available about androgenic effects, and the effects of testosterone on the cardiovascular system, endometrium, breast, and the liver will be reviewed here. An in-depth analysis of the relationship between androgens and behavior is beyond the scope of this review, and only passing reference to the effects of exogenous testosterone on behavior will be made. The sources used to identify studies included Ovid database and bibliographic citations in articles dealing with androgens and testosterone therapy in women.

Androgenic Effects

The effects of hirsutism—the growth of terminal hairs in the androgen-sensitive areas of the body—and acne are the predominant ones noted in women receiving physiological to slightly sup- raphysiological doses of androgens.

Hirsutism incidence depends in part upon the dose and duration, but not the route, of testosterone administration. Often 4-6 months of exposure are necessary to detect the increase in hair growth. Although the frequency of hirsutism in various studies of testosterone administration alone or with estrogen varies from 1% to 36% [4], most studies that have used testosterone to increase libido or treat vasomotor symptoms suggest that hirsutism is reported in 3-8% of those receiving doses that result in serum testosterone levels in the normal or slightly above normal range for reproductive-aged women [5-8]. In fact, in many of the randomized, double-blind studies of testosterone therapy in women receiving concomitant estrogens, no sig-nificant differences in reported or observed hir-sutism rates were noted between the women on testosterone plus estrogen and those on estrogen alone [9-12]. However, the lengths of those studies were 1 year or less, so it is unknown whether a difference would have emerged with a longer duration of exposure.

Acne has been reported in up to 45% of women receiving 10 mg of oral methyltestosterone daily, although most of the well-controlled studies dem-onstrate that less than 10% of women receiving physiological doses of testosterone note acne [5,6,8,13-18]. Also, in the short-term randomized, controlled trials, there was no significant difference in the occurrence of acne in those receiving testosterone plus estrogen over those receiving estrogen alone [10-12].

Virilization, which includes temporal hair recession, the development of clitoromegaly, increase in muscle mass, and deepening of the voice, is rare and is generally only seen when the serum testosterone levels are elevated several times above the upper limit of normal for women [19,20]. Thus, women with androgen-secreting tumors of the ovary or adrenal, women with the 21-hydroxylase form of congenital adrenal hyperplasia, and women who receive large amounts of testosterone as part of the female-to-male transsexual conversion do become virilized [21]. Virilization is usually not seen in women receiving more physiological doses of testosterone, and there have been no significant differences in reports of voice deepening, clitoromegaly, or alopecia in the double-blind, controlled, shortterm studies of testosterone administration to postmenopausal women with low libido [11,12].

Cardiovascular System

Endogenous Androgens and Cardiovascular Disease

Women with polycystic ovarian syndrome have been found to have an increased risk of the meta-bolic syndrome and cardiovascular disease [22]. Because hyperandrogenism is part of the syndrome, it has been speculated that the elevated testosterone concentrations may be a primary risk factor for these complications. However, the polycystic ovary model is complicated by the insulin resistance and hyperinsulinemia that many of these women exhibit.

Case-control studies of women with established coronary artery disease have shown either no dif-ference in testosterone levels between cases and controls or a significant relationship to free test-osterone levels. In cross-sectional or longitudinal community-based studies that examined the rela-tionship between androgen levels and coronary artery disease or markers of atherosclerosis, either no relationship, a decreased risk, or an increased risk has been reported [23]. Unfortunately, many of these studies did not adjust for the independent effect of estrogens and other factors. Because there is a positive correlation between testosterone and estrogen levels in many studies, failure to adjust for an estrogen effect is a major confounder. Barrett- Connor and Goodman-Gruen prospectively fol-lowed residents in Rancho Bernardo, CA, over 19 years, and examined the relationship between a variety of hormones measured from blood obtained at the time of enrollment and the risk of death from cardiovascular disease [24]. There were no differences in the age-adjusted hormone con-centrations in women with or without cardiovascular disease at baseline, and none predicted which women would develop or succumb to heart disease.

Exogenous Androgens and Cardiovascular Disease

There exist no long-term prospective studies that have been sufficiently powered to examine the car-diovascular risk of the exogenous administration of testosterone to women. No increased risk was identified in an examination of postmarketing data on a product containing esterified estrogens and 1.25 or 2.5 mg of methyltestosterone (Estratest®, Solvoy Pharmaceuticals, Marietta, GA, USA) [4]. Similarly, there was no increase in the frequency of myocardial infarction, hypertension, or cardiovas-cular deaths in 293 female-to-male transsexuals who received male testosterone replacement doses for 2 months to 41 years in comparison with the expected incidence in the population [25]. No increased risk of cardiovascular disease has been noted in the randomized, double-blind, placebocontrolled trials of testosterone given to women for low libido, but the short duration of treatment and relatively small numbers of women involved in the studies severely limit the ability of those studies to detect an increase in events in the testosterone-treated groups.

Blood Pressure

No relationship between blood pressure and endogenous androgen levels has been found in most of the epidemiological studies, with the exception of the Study of Women Across the Nation, in which a relationship between diastolic, but not systolic, blood pressure and total testoster-one and free androgen index was noted [26].

The various treatment trials with oral methylt-estosterone or testosterone undeconate, transder-mal patches, or subcutaneous testosterone pellets have not shown an increase in either systolic or diastolic blood pressure. Similarly, no increase in blood pressure has been noted in female-to- male transsexuals receiving large amounts of testosterone [21].

Lipids

The lipid alterations noted with exogenous test-osterone depend upon the route of administration, the dose, and whether testosterone is given alone or in combination with estrogens or estrogens and progestins. An increase in total cholesterol, low-density lipoprotein (LDL)-cholesterol, and triglycerides and a decrease in high-density lipo-protein (HDL)-cholesterol occur in female- to-male transsexuals receiving testosterone in sufficient concentrations to raise the serum testosterone into the upper part of the normal male range [21]. In contrast, when lower doses are given to postmenopausal women via injections or subcu-taneous implants along with estrogen, the total cholesterol, LDL-cholesterol, and triglycerides decrease, and the HDL-cholesterol increases [27]. Testosterone delivered transdermally in physi-ological doses along with estrogens is neutral in regards to lipids in comparison with the estrogen- only group.

Because of the first pass effect on the liver, oral testosterone given concomitantly with estrogens generally results in a mild decrease in total test-osterone and triglycerides, variable changes in LDL-cholesterol, and a decrease in HDL- cholesterol [27]. It is not known whether the net effect of these changers in regards to cardiovascular risk is positive, negative, or neutral.

Vascular Reactivity

High-dose testosterone administration to female- to-male transsexuals did not alter the flow- mediated vasodilatation measured following release of occlusion of the brachial artery in comparison with age-matched normal women, while there was a decrease in brachial artery dilatation following nitroglycerine in the transsexuals [28]. However, the transsexuals had a larger vascular diameter than did the controls, which may have confounded the interpretation. Both flow- mediated vasodilatation and nitroglycerine- induced vasodilatation were enhanced in women on stable estrogen treatment who were studied 6 weeks after receiving subcutaneous implants of 50 mg of testosterone [29]. Thus, physiological doses of androgens appear to have beneficial effects on vascular reactivity in women.

Viscosity

An increase in blood viscosity, which is mostly determined by the concentrations of triglycerides and fibrinogen, raises the risk of cardiovascular disease. In one study of 20 women receiving 2.5 mg of oral methyltestosterone along with 1.25 mg of esterified estrogens, the viscosity decreased significantly, which appeared to be primarily related to a decrease in the triglycerides, because fibrinogen levels increased [30]. No significant changes in viscosity have been noted in the trials using transdermal testosterone [3].

Coagulation Factors

A hypercoagulable state from either an excess of coagulation factors or a decrease in fibrinolytic activity may lead to cardiovascular disease. In a study that examined the effect following 2 years of use of subcutaneous testosterone implants of 100 mg replaced every 6 months in comparison with age-matched women, there were no significant differences in the levels of fibrinogen, or other thrombotic or fibrinolytic proteins, nor was there a difference in prothrombin time [31]. A slight antithrombotic effect was noted following large doses of testosterone given to female-to- male transsexuals [32].

Polycythemia

Polycythemia, which is a risk factor for cardiovas-cular disease, has been noted in some hypogonadal men receiving large doses of testosterone. However, this has not been found in women receiving physiological doses of testosterone given either by injection, subcutaneous implants, trans- dermally, or by the oral route. The large doses of testosterone used to treat female-to-male transsexuals only increase the hemoglobulin to the level seen in normal men [33].

Insulin Resistance

Insulin resistance is present in many women with endogenous hyperandrogenism associated with polycystic ovary syndrome, and such resistance is associated with the metabolic syndrome and is a major cardiovascular risk factor. Insulin is a stimulus for androgen secretion from the ovarian theca cells. Whether hyperandrogenemia causes insulin resistance has been the subject of several studies. Using the hyperinsulinemic, hyperglycemic, and/or euglycemic clamp methods in normal women receiving 15 mg of methyltestosterone daily or female-to-male transsexuals receiving high doses of intramuscular testosterone, a decrement in whole-body glucose uptake has been noted with supraphysiological, but not with physiological, insulin levels [28,34,35]. In transdermal testosterone trials in bilaterally oopho- rectomized women receiving estrogen, and in HIV-infected women with weight loss, basal insulin and glucose levels remained unchanged, and in the latter group there were no alterations in insulin sensitivity during an intravenous glucose tolerance test [9-12,36,37]. On the whole, these studies offer reassurance that testosterone administration in near physiological doses will not lead to insulin resistance and its adverse consequences.

Endometrium

Numerous studies have documented that prolonged exposure of endogenous or exogenous estrogens on the endometrium without the protective effects that endogenous progesterone or exogenous progestogens confer, increases the risk of endometrial proliferation and neoplasia [38].

Although in vitro data indicate that androgens antagonize the effects of estrogens on endometrial cells, there is a concern that the high aromatiza- tion ability of the endometrium may convert exogenous testosterone to estrogen locally and adversely affect the uterus [39]. Endogenous testosterone levels have not been shown to be associated with the risk of endometrial carcinoma, when the data are appropriately adjusted for the independent effect of estrogen levels, which track with the androgen concentrations [40]. No increase in endometrial proliferation was found in women taking 1.25 mg of methyltestosterone daily along with esterified estrogens vs. women taking esteri- fied estrogens alone [6]. In women with natural menopause taking concurrent estrogens and progestins, there were no adverse effects of transdermal testosterone on the uterus in comparison with women receiving placebo [41]. However, a cautionary note is raised by the finding that almost two-thirds of female-to-male transsexuals receiving testosterone enanthate developed a proliferative endometrium, including a few with cystic hyperplasia [42]. Thus, there are insufficient data concerning endometrial safety of aromatizable androgens at this time.

Breast

As with the uterus, there is a concern that the aromatase enzyme complex present in the breast fat and stromal tissue may utilize exogenous test-osterone to produce high local concentrations of estradiol that will stimulate breast glandular proliferation through a paracrine mechanism. However, androgens may inhibit growth of breast cancer cells in vitro as well as in breast cancer animal models [43]. Oophorectomized rhesus monkeys who receive estrogen add-back therapy have an increase in proliferation of breast epithelium, which is antagonized by physiological concentrations of testosterone [44].

Epidemiological studies that have attempted to correlate quartiles of endogenous testosterone concentrations with breast cancer risk are difficult to interpret. Some have shown an association, while others have not. Most studies that have adequately controlled for the confounding effects of estradiol levels and other variables have not shown a significant increase in risk [43]. Methodological problems also make it difficult to interpret the one prospective cohort study, or the three retrospective studies that have attempted to examine the risk [45-49]. Of importance, women with polycystic ovarian disease do not have an increase risk of breast cancer despite their chronically elevated testosterone levels.

Examination of mastectomy specimens from female-to-male transsexuals showed no important differences from breast tissue of normal women, adding further reassurance that androgen admin-istration may not increase the risk of breast cancer [50].

Liver

High doses of oral halogenated androgens have been associated with abnormalities in liver function and the development of peliosis hepatis and liver adenomas [25,51]. However, such abnormalities have not been found when more physiological doses of methyltestosterone are given. Transdermal testosterone also has not been associated with liver abnormalities [9-12].

Sleep Apnea

Although there is a theoretical risk based on the occurrence in some men with risk factors for sleep apnea following the institution of androgen replacement therapy, this problem has not been found in women.

Behavioral Changes

High doses of androgens given to men have been associated with aggressive behavior; however, clinical trials in women with more physiological testosterone treatment have not shown an associa-tion with adverse behavior. In a double-blind trial of injectable androgens, an increase in hostility scores was noted on a psychometric test [52]. Isolated reports of reversible aggressive behavior have been reported to the FDA, although neither the numerator nor denominator is known to estimate the true incidence of these findings [15].

Summary and Conclusions

The main adverse reactions to exogenous andro-gens given in physiological to slightly superphy-siological concentrations are androgenic side effects, primarily hirsutism and acne (Table 1). Virilization is generally not seen. Androgen treatment does not appear to have adverse cardiovascular effects, with the possible exception of a lowering of HDL-cholesterol with oral, but not parental or transdermal, androgens. The effects on the endometrium are unknown at this time because of a paucity of data. Although long-term safety in regards to the breast is unknown, the short-term studies, as well as the animal and in vitro data, provide some degree of reassurance. Studies in women who are not receiving concomitant estrogens or estrogens and androgens are also needed in order to dissect out the safety issues of testosterone alone.

Table 1. Summary of effects of exogenous testosterone treatment of postmenopausal women for low libido.

In conclusion, testosterone administered by the nonoral route, which results in serum levels of free testosterone that fall within the physiological range for women during the reproductive years, is safe for up to 2 years when given concomitantly with exogenous estrogens to postmenopausal women. Long-term prospective or postmarketing studies are required before firm conclusions about safety beyond this period can be made based upon adequate data. Also, because there are no androgen preparations approved by the FDA for the treat-ment of low libido in women, careful monitoring of serum testosterone levels is essential to avoid overtreatment with compounding pharmacy preparations or products prepared for androgen replacement in men. Finally, a trial of androgen administration should only be carried out in menopausal women after other causes of low libido have been eliminated or treated.

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