Impact of different GnRH analogs in benign gynecological disorders related to their chemical structure, delivery systems and dose

Pharmacokinetics and Bioavailability of the GnRH Analogs in the Form of Solution and Zn2+-Suspension After Single Subcutaneous Injection in Female Rats

BACKGROUND AND OBJECTIVES

Although many synthetic gonadoliberin analogs have been developed, only a few of them, including buserelin, were introduced into clinical practice. Dalarelin, which differs from buserelin by just one aminoacid in the position 6 (D-Ala), is not widely used so far. Gonadotropin-releasing hormone (GnRH) analogs are used to treat many different illnesses and are available in different forms like solution for injection, nasal spray, microspheres, etc. Unfortunately, none of the above drug formulations can release the hormones for 24 h. We assumed that classical suspension could solve this problem.

METHODS

Two sets of experiments were performed. In the first one, buserelin and dalarelin were injected into mature female rats in two forms: suspension, in which the analogs are bounded by Zn²⁺ ions and solution. The pharmacokinetic parameters and bioavailability of the analogs were calculated, based on their concentration in the plasma measured by high-performance liquid chromatography method (HPLC). In the second experiment, the hormones in two different forms were injected into superovulated immature female rats and then the concentration of Luteinizing hormone (LH), Follicle-stimulating hormone (FSH) and 17β-estradiol in the serum was measured by radioimmunological method.

RESULTS

The Extent of Biological Availability (EBA), calculated on the base of AUC_0-∞, showed that in the form of solution buserelin and dalarelin display, respectively, only 13 and 8 % of biological availability of their suspension counterparts. Comparing both analogs, the EBA of dalarelin was half (53 %) that of buserelin delivered in the form of solution and 83 % when they were delivered in the form of suspension. The injection of buserelin or dalarelin, in the form of solution or suspension, into superovulated female rats increased LH, FSH and estradiol concentration in the serum. However, after injection of the analogs in the form of suspension, the high concentration of LH and FSH in the serum persisted longer.

CONCLUSION

Performed studies indicate that GnRH analogs in the form of suspension have higher bioavailability than their solution counterparts. It influences the effects of their action, especially in relation to LH and FSH.

Triptorelin for the treatment of endometriosis

INTRODUCTION

Over the past 30 years, gonadotropin-releasing hormone agonists (GnRH-a) have been used to induce a hypoestrogenic status in women with endometriosis with the aim to cause an improvement in pain symptoms similar to that observed after menopause. Triptorelin is one of the most commonly used GnRH-a.

AREAS COVERED

This review offers an explanation of the mechanism of action, of the pharmacokinetics and pharmacodynamics of triptorelin and gives the readers a complete overview of the studies on the clinical efficacy, tolerability and safety of this agent in patients with endometriosis.

EXPERT OPINION

The studies reviewed in the current manuscript demonstrate the efficacy of triptorelin in improving pain symptoms caused by endometriosis. Further, this effect is confirmed by the reduction in the volume of the endometriotic nodules during treatment. Future research should evaluate whether the pre-operative administration of triptorelin prior to surgical excision of endometriomas may be useful in preserving the ovarian reserve.

A prospective randomized study comparing endocrinological and clinical effects of two types of GnRH agonists in cases of uterine leiomyomas or endometriosis

OBJECTIVE

In order to assess the endocrinological changes associated with 2 types of low-dose GnRH agonists depot as well as their clinical efficacy, we performed a randomized prospective comparison study of patients having uterine leiomyomas or endometriosis.

METHODS

A prospective randomized study involving 67 patients with uterine leiomyomas or endometriosis was carried out. These patients were randomly administered either buserelin MP 1.8 mg (Group B, n = 34) or leuprolide 1.88 mg (Group L, n = 33). In each group we evaluated the symptoms of genital bleeding and hot flashes during GnRHa treatment, as well as the levels of serum LH, FSH, and estradiol 8 weeks after the start of treatment. In addition, the endometrial thickness was measured by transvaginal ultrasonography, and changes in the volume of the uterine leiomyoma or endometrial cyst at the end of treatment. The GnRHa depot was administered from 3 to 8 times, 28 days apart, in both groups.

RESULTS

The incidence of menstruation-like genital bleeding 8 weeks after treatment was significantly (p < 0.01) higher in Group B. However this difference disappeared by 12 weeks after treatment. The climacteric symptom of hot flashes was found to be significantly (p < 0.01) more severe in Group L, and this tendency continued until 20 weeks after treatment. The 2 groups did not differ significantly with regard to the levels of the serum LH, FSH, and estradiol at 8 weeks after treatment or in the endometrial thickness at the end of the GnRHa treatment. In both groups, the volumes of the uterine leiomyomas were significantly (p < 0.01) lower after the treatment. In contrast, the volumes of the endometrial cysts did not decrease after administration of GnRHa in both groups.

CONCLUSION

Leuprolide 1.88 induced pituitary down regulation more rapidly than buserelin MP. However the hypoestrogenic symptoms such as hot flashes were more severe in cases treated with leuprolide 1.88 than in those treated with buserelin MP. Our data confirm that the therapeutic efficacy of buserelin MP and leuprolide 1.88 are similar, with both being sufficient to treat uterine leiomyomas and endometriosis.