"Nov. 20, 2012 -- Oral contraceptives should be made available without a prescription to reduce unintended pregnancies, according to a newly published opinion by the American College of Obstetricians and Gynecologists (ACOG).
Mechanism of Action
COCs lower the risk of becoming pregnant primarily by suppressing ovulation. Other possible mechanisms may include cervical mucus changes that inhibit sperm penetration and endometrial changes that reduce the likelihood of implantation.
The estrogen in Natazia is estradiol valerate, a synthetic prodrug of 17ß-estradiol. The progestin in Natazia is dienogest (DNG). DNG displays properties of 19-nortestosterone derivatives as well as properties associated with progesterone derivatives. [See Nonclinical Toxicology.]
The effect of Natazia on QT prolongation was evaluated in a randomized, double-blind, positive (moxifloxacin 400 mg) and negative (placebo) controlled crossover study in healthy subjects. A total of 53 subjects were administered Natazia (containing 3 mg dienogest and 2 mg estradiol valerate), dienogest 10 mg, and placebo as once daily doses for 4 days, and moxifloxacin 400 mg as a single oral dose. The upper bound of the 90% confidence interval for the largest placebo-adjusted, baseline-corrected QTc based on Fridericia's correction method (QTcF) was below 10 msec, the threshold for regulatory concern.
After oral administration of estradiol valerate, cleavage to 17β-estradiol and valeric acid takes place during absorption by the intestinal mucosa or in the course of the first liver passage. This gives rise to estradiol and its metabolites, estrone and other metabolites. Maximum serum estradiol concentrations of 73.3 pg/mL are reached at a median of approximately 6 hours (range: 1.5–12 hours) and the area under the estradiol concentration curve [AUC(0–24hr)] was 1301 pg·hr/mL after single ingestion of a tablet containing 3 mg estradiol valerate under fasted condition on Day 1 of the 28-day sequential regimen.
Bioavailability of dienogest is about 91%. Maximum serum dienogest concentrations of 91.7 ng/mL are reached at a median of approximately 1 hour (range: 0.5–1.5 hour) and the area under the dienogest concentration curve [AUC(0– 24hr)] was 964 ng/mL after single oral administration of Natazia tablet containing 2 mg estradiol valerate/3 mg dienogest under fasted condition. The pharmacokinetics of dienogest are dose-proportional within the dose range of 1–8 mg. Steady state is reached after 4 days of the same dosage of 2 mg dienogest. The mean accumulation ratio for AUC (0–24hr) is approximately 1.24.
The mean plasma pharmacokinetic parameters at steady state following repeated oral doses of a 2 mg estradiol valerate/3 mg dienogest combination tablet in fertile women under fasted condition are reported in Table 1.
Table 1: Arithmetic Mean (SD) Serum
Pharmacokinetic Parameters at Steady-state (on Day 24) following Repeated Oral
Doses of 2 mg EV/3 mg DNG on Days 8–24 of the 28 day Regimen in Fertile Women
under Fasted Condition (N=15)
|Cmax||85.2 (19.7) ng/ml||70.5 (25.9) pg/ml||483 (198) pg/ml|
|Tmax (hr)a||1.5 (1–2)||3 (1.5–12)||4 (3–12)|
|AUC(0–24hr)||828 (187) ng•hr/ml||1323 (480) pg•hr/ml||7562 (3403) pg•hr/ml|
|t½ (hr)||12.3 (1.4)||NA||NA|
|aMedian (range) for Tmax
Cmax = Maximum serum concentration
Tmax = Time to reach maximum concentration
AUC(0–24hr) = Area under the concentration-time curve from 0 hr data point up to 48 hr post-administration
NA: Data not available
Concomitant food intake in women resulted in a 28% decrease for dienogest Cmax and 23% increase of estradiol Cmax while the exposure (AUC) of both dienogest and estradiol did not change.
In serum, 38% of estradiol is bound to sex hormone-binding globulin (SHBG), 60% to albumin and 2–3% circulates in free form. An apparent volume of distribution of approximately 1.2 L/kg was determined after intravenous (IV) administration.
A relatively high fraction (10%) of circulating dienogest is present in the free form, with approximately 90% being bound non-specifically to albumin. Dienogest does not bind to SHBG and corticosteroid-binding globulin (CBG). The volume of distribution at steady state (Vd,ss) of dienogest is 46 L after the IV administration of 85 mcg 3H-dienogest.
After oral administration of estradiol valerate, approximately 3% of the dose is directly bioavailable as estradiol. Estradiol undergoes an extensive first-pass effect and a considerable part of the dose administered is already metabolized in the gastrointestinal mucosa. The CYP 3A family is known to play the most important role in human estradiol metabolism. Together with the pre-systemic metabolism in the liver, about 95% of the orally administered dose becomes metabolized before entering the systemic circulation. The main metabolites are estrone and its sulfate or glucuronide conjugates.
Dienogest is extensively metabolized by the known pathways of steroid metabolism (hydroxylation, conjugation), with the formation of endocrinologically mostly inactive metabolites. CYP3A4 was identified as a predominant enzyme catalyzing the metabolism of dienogest.
Dienogest is mainly excreted renally in the form of metabolites and unchanged dienogest is the dominating fraction in plasma. The terminal half-life of dienogest is approximately 11 hours.
Use In Specific Populations
Safety and efficacy of Natazia has been established in women of reproductive age. Efficacy is expected to be the same for postpubertal adolescents under the age of 18 and for users 18 years and older. Use of this product before menarche is not indicated.
Natazia has not been studied in postmenopausal women and is not indicated in this population.
The pharmacokinetics of Natazia has not been studied in subjects with renal impairment.
The pharmacokinetics of Natazia has not been studied in subjects with hepatic impairment. Steroid hormones may be poorly metabolized in patients with impaired liver function. Acute or chronic disturbances of liver function may necessitate the discontinuation of COC use until markers of liver function return to normal. [See CONTRAINDICATIONS and WARNINGS AND PRECAUTIONS.]
Body Mass Index
The efficacy of Natazia in women with a BMI of > 30 kg/m² has not been evaluated.
Consult the labeling of all concurrently used drugs to obtain further information about interactions with oral contraceptives or the potential for enzyme alterations.
Effects of Other Drugs on Combined Oral Contraceptives
Drugs or herbal products that induce certain enzymes, including CYP3A4, may decrease the effectiveness of COCs or increase breakthrough bleeding. Some drugs or herbal products that may decrease the effectiveness of hormonal contraceptives include barbiturates, bosentan, felbamate, griseofulvin, oxcarbazepine, and topiramate. Counsel women to use an alternative method of contraception or a back-up method when moderate or weak enzyme inducers are used with COCs, and to continue back-up contraception for 28 days after discontinuing the enzyme inducer to ensure contraceptive reliability.
Dienogest is a substrate of CYP3A4. Women who take medications that are strong CYP3A4 inducers (for example, carbamazepine, phenytoin, rifampicin, and St. John's wort) should not choose Natazia as their oral contraceptive while using these inducers and for at least 28 days after discontinuation of these inducers due to the possibility of decreased contraceptive efficacy.
The effect of the CYP3A4 inducer rifampicin was studied in an open-label, non-randomized, single center study in 16 healthy postmenopausal women. All volunteers received a treatment regimen of 2 mg estradiol valerate and 3 mg dienogest combination tablets, dosed once daily over 17 days, and of rifampicin, which was administered once daily in an oral dose of 600 mg on Days 12 to 16. 24–hr pharmacokinetics of estradiol and dienogest on Days 11 and 17 were compared. Co-administration of rifampicin with estradiol valerate/dienogest tablets led to a 52 % and 83% decrease in the mean Cmax and AUC(0–24hr), respectively, for dienogest and a 25% and 44% decrease in Cmax and AUC(0–24hr), respectively, for estradiol at steady state.
Strong CYP3A4 Inhibitors
Strong CYP3A4 inhibitors such as ketoconazole increase hormone serum concentrations. The effect of a strong CYP3A4 inhibitor, ketoconazole, on dienogest and estradiol pharmacokinetics was studied in an open-label, two parallel-groups, one-sequence, one-way crossover study in healthy postmenopausal Caucasian women. One tablet of 2 mg estradiol valerate and 3 mg dienogest was administered orally once a day for 14 days. Twelve volunteers received an oral dose of 400 mg ketoconazole (that is, 2 tablets containing 200 mg ketoconazole) once daily for 7 days (Days 8–14). Twenty-four hour pharmacokinetics of estradiol and dienogest on Days 7 and 14 were compared. Coadministration with the strong inhibitor ketoconazole resulted in a 186% and 57% increase of AUC (0–24hr) at steady state for dienogest and estradiol. There was also a 94% and 65% increase of Cmax at steady state for dienogest and estradiol when co-administered with ketoconazole.
Moderate CYP3A4 Inhibitors
Moderate CYP3A4 inhibitors such as erythromycin increase hormone serum concentrations. The effect of a moderate CYP3A4 inhibitor, erythromycin on dienogest and estradiol pharmacokinetics was studied in an open-label, two parallel-groups, one-sequence, one-way crossover study in healthy postmenopausal Caucasian women. One tablet of 2 mg estradiol valerate and 3 mg dienogest was administered orally once a day for 14 days. Twelve volunteers received an oral dose of 500 mg erythromycin three times a day for 7 days (Days 8–14). Twenty-four hour pharmacokinetics of estradiol and dienogest on Days 7 and 14 were compared. When co-administered with the moderate inhibitor erythromycin, the AUC (0–24hr) of dienogest and estradiol at steady state were increased by 62% and 33%, respectively. There was also a 33% and 51% increase of Cmax at steady state for dienogest and estradiol when coadministered with erythromycin.
Other known CYP3A4 inhibitors such as azole antifungals, cimetidine, verapamil, macrolides, diltiazem, antidepressants, and grapefruit juice may increase plasma levels of dienogest and estradiol.
HIV/HCV Protease Inhibitors and non-nucleoside reverse transcriptase inhibitors
Significant changes (increase or decrease) in the plasma concentrations of the estrogen and progestin have been noted in some cases of co-administration of HIV/HCV protease inhibitors or with non-nucleoside reverse transcriptase inhibitors.
There have been reports of pregnancy while taking hormonal contraceptives and antibiotics, but clinical pharmacokinetic studies have not shown consistent effects of antibiotics on plasma concentrations of synthetic steroids.
Effects of Combined Oral Contraceptives on Other Drugs
COCs containing ethinyl estradiol may inhibit the metabolism of other compounds. COCs have been shown to significantly decrease plasma concentrations of lamotrigine, likely due to induction of lamotrigine glucuronidation. This may reduce seizure control; therefore, dosage adjustments of lamotrigine may be necessary. Consult the labeling of the concurrently-used drug to obtain further information about interactions with COCs or the potential for enzyme alterations.
In vitro studies with human CYP enzymes did not indicate an inhibitory potential of dienogest at clinically relevant concentrations.
Oral Contraceptive Clinical Trials
The study conducted in North America (U.S. and Canada) was a multicenter, open-label, single-arm, unintended pregnancy study. There were 490 healthy subjects between 18 and 35 years of age (mean age: 25.1 years) who were treated for up to 28 cycles of 28 days each. The racial demographic of enrolled women was: Caucasian (76%), Hispanic (13%), African-American (7%), Asian (3%), and Other (1%). The weight range for treated women was 40 to 100 kg (mean weight: 62.5 kg) and the BMI range was 14 to 30 kg/m2 (mean BMI: 23.3 kg/m2). Of treated women, 15% discontinued the study treatment due to an adverse event, 13% were lost to follow up, 10% withdrew their consent, 8% discontinued due to other reason, 1% discontinued due to protocol deviation, and 1% discontinued due to pregnancy.
The study conducted in Europe (Germany, Austria and Spain) was a multicenter, open-label, single-arm contraceptive reliability study. There were 1,377 healthy subjects between 18 and 50 years of age (mean age: 30.3 years) who were treated for 20 cycles of 28 days each. The racial demographic of enrolled women was predominantly Caucasian (99.2%). The weight range for treated women was 38 to 98 kg (mean weight: 63.8 kg) and the BMI range was 15 to 31.8 kg/m2 (mean BMI: 22.8 kg/m2). Of treated women, 10% discontinued the study treatment due to an adverse event, 5% discontinued due to other reason, 2% were lost to follow up, 2% discontinued due to protocol deviation, 2% withdrew their consent, and 1% discontinued due to pregnancy.
The Pearl Index (PI) was the primary efficacy endpoint used to assess contraceptive reliability and was assessed in each of the two studies, assuming all subjects were at risk of pregnancy in all medication cycles unless back-up contraception was documented. The PI is based on pregnancies that occurred after the onset of treatment and within 7 days after the last pill intake. Cycles in which conception did not occur, but which included the use of back-up contraception, were not included in the calculation of the PI. The PI also includes patients who did not take the drug correctly. The estimated PI for the North American study is 1.64 and the estimated PI for the European study is 1.04. The Kaplan-Meier method was also used to calculate the contraceptive failure rate.
The summary of the Pearl Indexes and cumulative contraceptive failure rates are provided in Table 2:
Table 2: Summary of the Pearl Indexes and the Cumulative
Contraceptive Failure Rates
|Study||Age Group||Relative Treatment Exposure Cycles1||Number of Pregnancies within 13 Cycles and 7 Days after Last Treatment||Pearl Index||Upper Limit of 95% CI||Contraceptive Failure Rate at the End of First Year|
|1Total treatment exposure time without back-up contraception|
Last reviewed on RxList: 2/28/2012
This monograph has been modified to include the generic and brand name in many instances.
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