Letrozole Versus Letrozole and Inositol

Polycystic Ovary Syndrome

Polycystic ovary syndrome (PCOS) is one of the most common endocrine and metabolic disorders affecting women of reproductive age. Its prevalence varies considerably according to the population studied and the diagnostic criteria applied. A recent global systematic review and meta-analysis estimated the prevalence of PCOS among adult women to be approximately 12.1% according to the Rotterdam criteria, compared with 7.9% using the National Institutes of Health (NIH) criteria and 12.7% using the Androgen Excess-PCOS Society criteria.

PCOS is a heterogeneous disorder characterized primarily by ovulatory dysfunction, clinical and/or biochemical hyperandrogenism, and polycystic ovarian morphology, after exclusion of other disorders that may present with similar features. Clinically, affected women may present with irregular menstrual cycles, hirsutism, acne, infertility, and weight-related problems. In addition to its reproductive manifestations, PCOS is associated with important metabolic abnormalities, particularly insulin resistance, compensatory hyperinsulinemia, dyslipidemia, and an increased risk of impaired glucose tolerance and type 2 diabetes mellitus. The pathophysiology of PCOs is complex and multifactorial and involves interactions among genetic susceptibility, neuroendocrine dysfunction, ovarian steroidogenesis, metabolic abnormalities, and environmental influences.Hyperandrogenism and insulin resistance are considered major components of this pathophysiological network. Increased ovarian androgen production contributes to abnormal follicular development and ovulatory dysfunction, whereas insulin resistance and the resulting hyperinsulinemia may further stimulate androgen production by ovarian theca cells and reduce hepatic sex hormone-binding globulin synthesis, thereby increasing circulating bioavailable androgens. These mechanisms may create a self-perpetuating relationship between metabolic dysfunction, hyperandrogenism, and impaired follicular maturation.Ovulatory dysfunction is one of the principal causes of infertility among women with PCOS, and PCOS has been reported to account for up to approximately 80% of cases of anovulatory infertility. Consequently, restoration of ovulation represents a major therapeutic objective in women with PCOS who desire pregnancy. Current international evidence-based recommendations identify letrozole as the first-line pharmacological treatment for ovulation induction in women with PCOS-associated anovulatory infertility in the absence of other infertility factors. Letrozole is a third-generation aromatase inhibitor that temporarily suppresses the conversion of androgens to estrogens. The resulting reduction in circulating estrogen diminishes estrogen-mediated negative feedback at the hypothalamic-pituitary level, leading to increased endogenous follicle-stimulating hormone (FSH) secretion and subsequent recruitment and development of ovarian follicles. Unlike clomiphene citrate, letrozole has a relatively short half-life and does not exert prolonged anti-estrogenic effects on the endometrium or cervical mucus, which may contribute to its favorable reproductive outcomes. Nevertheless, despite its established efficacy, a proportion of women with PCOS fail to develop a dominant follicle or achieve ovulation following conventional letrozole treatment. Such patients are commonly described as having letrozole-resistant PCOS, although the precise definition of letrozole resistance and the optimal management strategy remain areas of ongoing investigation. Several therapeutic modifications have therefore been investigated in an attempt to improve ovarian responsiveness in women who do not respond adequately to conventional letrozole regimens. One approach is to target the metabolic abnormalities that may contribute to impaired ovarian responsiveness. Inositols, particularly myo-inositol (MI) and D-chiro-inositol (DCI), have attracted considerable interest because of their roles as intracellular second messengers in insulin-signaling pathways and their potential influence on ovarian steroidogenesis and follicular function. MI is involved in glucose uptake and FSH signaling within the ovary, whereas DCI participates in insulin-mediated metabolic pathways and may influence ovarian androgen synthesis Abnormalities in inositol metabolism have therefore been proposed as one potential link between insulin resistance and reproductive dysfunction in PCOs. From a pathophysiological perspective, combining inositol supplementation with letrozole could theoretically provide complementary effects in women with PCOS. Letrozole primarily promotes follicular recruitment through transient estrogen suppression and increased endogenous FSH secretion, whereas inositol supplementation may improve insulin signaling and potentially modify the metabolic and hormonal ovarian environment. Improvement in insulin sensitivity and reduction of compensatory hyperinsulinemia could theoretically decrease excessive ovarian androgen production and thereby enhance follicular responsiveness. Nevertheless, robust evidence demonstrating that the addition of inositol to letrozole is superior to optimized letrozole therapy alone, particularly among women with documented letrozole resistance, remains insufficient. The benefit of this combined strategy therefore requires further evaluation in appropriately designed comparative clinical studies.

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