Climara PRO (Estradiol / Levonorgestrel Transdermal) - Description and Clinical Pharmacology

DESCRIPTION

Climara Pro™ (Estradiol/Levonorgestrel Transdermal System) is an adhesive-based matrix transdermal patch designed to release both estradiol and levonorgestrel, a progestational agent, continuously upon application to intact skin.

The 22 cm²Climara Pro system contains 4.40 mg estradiol and 1.39 mg levonorgestrel and provides a nominal delivery rate (mg per day) of 0.045 estradiol and 0.015 levonor-gestrel.

Estradiol USP has a molecular weight of 272.39 and the molecular formula is C₁₈H₂₄O₂.

Levonorgestrel USP has a molecular weight of 312.4 and a molecular formula of C₂₁H₂₈O₂.

The structural formulas for estradiol and levonorgestrel are:

The Climara Pro system comprises 3 layers. Proceeding from the visible surface towards the surface attached to the skin, these layers are (1) a translucent polyethylene backing film, (2) an acrylate adhesive matrix containing estradiol and levonorgestrel, and (3) a protective liner of either siliconized or fluoropolymer coated polyester film. The protective liner is attached to the adhesive surface and must be removed before the system can be used.

The active components of the system are estradiol and levonorgestrel. The remaining components of the system (acrylate copolymer adhesive and polyvinylpyrrolidone/vinyl acetate copolymer) are pharmacologically inactive.

CLINICAL PHARMACOLOGY

Endogenous estrogens are largely responsible for the development and maintenance of the female reproductive system and secondary sexual characteristics. Although circulating estrogens exist in a dynamic equilibrium of metabolic interconversions, estradiol is the principal intracellular human estrogen and is substantially more potent than its metabolites, estrone and estriol, at the receptor level.

The primary source of estrogen in normally cycling adult women is the ovarian follicle, which secretes 70 to 500 mcg of estradiol daily, depending on the phase of the menstrual cycle. After menopause, most endogenous estrogen is produced by conversion of androstenedione, secreted by the adrenal cortex, to estrone by peripheral tissues. Thus, estrone and the sulfate conjugated form, estrone sulfate, are the most abundant circulating estrogens in postmenopausal women.

Estrogens act through binding to nuclear receptors in estrogen-responsive tissues. To date, two estrogen receptors have been identified. These vary in proportion from tissue to tissue.

Circulating estrogens modulate the pituitary secretion of the gonadotropins, luteinizing hormone (LH) and follicle stimulating hormone (FSH), through a negative feedback mechanism. Estrogens act to reduce the elevated levels of these hormones seen in postmenopausal women.

Levonorgestrel inhibits gonadotropin production result-ing in retardation of follicular growth and inhibition of ovulation.

Studies to assess the potency of progestins using estrogen-primed postmenopausal endometrial biochemistry and morphologic features have shown that levonorgestrel counteracts the proliferative effects of estrogens on the endometrium.

PHARMACOKINETICS

Absorption: Administration of Climara Pro to postmenopausal women produces mean maximum estradiol concentrations in serum in about 2 to 2.5 days. Estradiol concentrations equivalent to the normal ranges observed at the early follicular phase in premenopausal women are achieved within 12-24 hours after the first application.

In one study, steady state estradiol concentrations in serum were measured during week 4 in 44 healthy, postmenopausal women during four consecutive Climara Pro applications of two formulations (0.045 mg estradiol/0.030 mg levonorgestrel and 0.045 mg estradiol/0.015 mg levonor-gestrel) to the abdomen (each dose was applied for four 7-day periods). Both formulations were bioequivalent in terms of estradiol and estrone C_max and AUC parameters. A summary of Climara Pro single and multiple applications estradiol, estrone and levonorgestrel pharmacokinetic parameters is shown in Table 1.

All mean parameters are arithmetic means except T_max which is expressed as the median.

At steady state, Climara Pro maintains during the application period an average serum estradiol concentration of 35.7 pg/mL as depicted in Figure 1.

Following the application of the Climara Pro transdermal system, levonorgestrel concentrations are maximum in about 2.5 days. At steady state, Climara Pro maintains during the application period an average serum levonorgestrel concentration of 166 pg/mL as depicted in Figure 2. The mean levonorgestrel pharmacokinetic parameters of Climara Pro are summarized in Table 1.

DISTRIBUTION

The distribution of exogenous estrogens is similar to that of endogenous estrogens. Estrogens are widely distributed in the body and are generally found in higher concentrations in the sex hormone target organs. Estrogens circulate in the blood largely bound to sex hormone binding globulin (SHBG) and albumin.

Levonorgestrel in serum is bound to both SHBG and albumin. Following four consecutive weekly applications of Climara Pro mean (± SD) SHBG concentrations declined from a predose value of 47.5 (25.8) to 41.2 (22.4) nmol/L at week 4.

METABOLISM

Exogenous estrogens are metabolized in the same manner as endogenous estrogens. Circulating estrogens exist in a dynamic equilibrium of metabolic interconversions. These transformations take place mainly in the liver. Estradiol is converted reversibly to estrone, and both can be converted to estriol, which is the major urinary metabolite. Estrogens also undergo enterohepatic recirculation via sulfate and glucuronide conjugation in the liver, biliary secretion of conjugates into the intesine, and hydrolysis in the gut followed by reabsorption. In postmenopausal women, a significant proportion of the circulating estrogens exist as sulfate conjugates, especially estrone sulfate, which serves as a circulating reservoir for the formation of more active estrogens.

The most important metabolic pathway for levonorgestrel occurs in the reduction of the 4- and the 3-oxo-group as well as hydroxylations at positions 2(alpha), 1(beta), and 16(beta), followed by conjugation. Most of the metabolites that circulate in the blood are sulfates of 3, 5(beta)-tetrahydro-levonorgestrel, while excretion occurs predominantly in the form of glucuronides. Some of the parent levonorgestrel also circulates as the 17(beta)-sulfate. In-vitro studies on the biotransformation of levonorgestrel in human skin did not indicate any significant metabolism of levonorgestrel during skin penetration.

EXCRETION

Estradiol, estrone, and estriol are excreted in the urine along with glucuronide and sulfate conjugates. Following patch removal, serum estradiol concentrations decline rapidly with a mean (± SD) terminal half-life of 3.0 ± 0.67 hours.

Levonorgestrel and its metabolites are primarily excreted in the urine. Mean (± SD) terminal half-life for levonorgestrel was determined to be 28 ± 6.4 hours.

DRUG INTERACTIONS

In-vitro and in-vivo studies have shown that estrogens are metabolized partially by cytochrome P450 3A4 (CYP3A4). Therefore, inducers or inhibitors of CYP3A4 may affect estrogen drug metabolism. Inducers of CYP3A4 such as St. John's Wort preparations (Hypericum perforatum), phenobarbital, carbamazepine, and rifampin may reduce plasma concentrations of estrogens, possibly resulting in a decrease in therapeutic effects and/or changes in the uterine bleeding profile. Inhibitors of CYP3A4 such as erythromycin, clarithromycin, ketoconazole, itraconazole, ritonavir and grapefruit juice may increase plasma concentrations of estrogens and may result in side effects.

Hydroxylation of levonorgestrel is a conversion step which is mediated by cytochrome P450 enzymes. Based on in-vitro and in-vivo studies, it can be assumed that CYP3A, CYP2E and CYP2C are involved in the metabolism of levonor-gestrel. Likewise, inducers or inhibitors of these enzymes may either, respectively, decrease the therapeutic effects or result in side effects.

SPECIAL POPULATIONS

Climara Pro has been studied only in healthy postmenopausal women.

CLINICAL STUDIES

EFFECTS ON VASOMOTOR SYMPTOMS

The efficacy of 0.045 mg estradiol/0.030 mg levonorgestrel administered weekly versus placebo in the relief of moderate to severe vasomotor symptoms in post-menopausal women was studied in one 12-week clinical trial (n=183, average age 52.1 ± 4.93, 82.0% Caucasian). The 0.045 mg estradiol/0.030 mg levonorgestrel dosage strength was shown to be statistically better than placebo at weeks 4 and 12 for relief of both the number and severity of moderate to severe hot flushes. See Tables 2 and 3. Climara Pro and the 0.045 mg estradiol/0.030 mg levonorgestrel dosage strength are bioequivalent in terms of estradiol delivery. (See CLINICAL PHARMACOLOGY, Pharmacokinetics.)

EFFECTS ON THE ENDOMETRIUM

In a 1-year clinical trial of 412 postmenopausal women (with intact uteri) treated with a continuous regimen of Climara Pro or with a continuous estradiol-only transdermal system, results of evaluable endometrial biopsies show that no hyperplasia was seen with Climara Pro. Table 4 below summarizes these results (Intent-to-Treat populations).

EFFECTS ON UTERINE BLEEDING OR SPOTTING

The effects of Climara Pro on uterine bleeding or spotting, as recorded using an interactive voice response system, were evaluated in one 12-month clinical trial. Results are shown in Figure 3.

Percent based upon the number of subjects with data

Last non-missing cycle carried forward through cycle 13

Bleeding associated with endometrial biopsies not included

WOMEN'S HEALTH INITIATIVE STUDIES

The Women's Health Initiative (WHI) enrolled a total of 27,000 predominantly healthy postmenopausal women to assess the risks and benefits of either the use of 0.625 mg conjugated estrogens (CE) per day alone or the use of 0.625 mg conjugated equine estrogens plus 2.5 mg medroxyprogesterone acetate (MPA) per day compared to placebo in the prevention of certain chronic diseases. The primary endpoint was the incidence of coronary heart disease (CHD) (nonfatal myocardial infarction and CHD death), with invasive breast cancer as the primary adverse outome studied. A "global index" included the earliest occurrence of CHD, invasive breast cancer, stroke, pulmonary embolism (PE), endometrial cancer, colorectal cancer, hip fracture, or death due to other cause. The study did not evaluate the effects of CE or CE/MPA on menopausal symptoms.

The CE-only substudy is continuing and results have not been reported. The CE/MPA substudy was stopped early because, according to the predefined stopping rule, the increased risk of breast cancer and cardiovascular events exceeded the specified benefits included in the "global index." Results of the CE/MPA substudy, which included 16,608 women (average age of 63 years, range 50 to 79; 83.9% White, 6.5% Black, 5.5% Hispanic), after an average follow-up of 5.2 years are presented in Table 5 below:

For those outcomes included in the "global index," absolute excess risks per 10,000 person-years in the group treated with CE/MPA were 7 more CHD events, 8 more strokes, 8 more PEs, and 8 more invasive breast cancers, while absolute risk reductions per 10,000 person-years were 6 fewer colorectal cancers and 5 fewer hip fractures. The absolute excess risk of events included in the "global index" was 19 per 10,000 person-years. There was no difference between the groups in terms of all-cause mortality. (See BOX WARNING, WARNINGS, and PRECAUTIONS.)