Comparative pharmacokinetics of levonorgestrel and ethinyloestradiol following intravenous, oral and vaginal administration

A Physiologically-Based Pharmacokinetic Simulation to Evaluate Approaches to Mitigate Efavirenz-Induced Decrease in Levonorgestrel Exposure with a Contraceptive Implant

Background: Levonorgestrel implant is a highly effective hormonal contraceptive, but its efficacy may be compromised when used with cytochrome enzyme inducers such as efavirenz. The primary aim of this study was to evaluate methods of mitigating the drug interaction. Methods: Using a physiologically-based pharmacokinetic (PBPK) model for levonorgestrel that we developed within the Simcyp® program, we evaluated a higher dose of levonorgestrel implant, a lower dose of efavirenz, and the combination of both, as possible methods to mitigate the interaction. In addition, we investigated the impact on levonorgestrel total and unbound concentrations of other events likely to be associated with efavirenz coadministration: changes in plasma protein binding of levonorgestrel (as with displacement) and high variability of efavirenz exposure (as with genetic polymorphism of its metabolism). The range of fraction unbound tested was 0.6% to 2.6%, and the range of efavirenz exposure ranged from the equivalent of 200 mg to 4800 mg doses. Results: Levonorgestrel plasma concentrations at any given time with a standard 150 mg implant dose are predicted to be approximately 68% of those of control when given with efavirenz 600 mg and 72% of control with efavirenz 400 mg. With double-dose levonorgestrel, the predictions are 136% and 145% of control, respectively. A decrease in levonorgestrel plasma protein binding is predicted to primarily decrease total levonorgestrel plasma concentrations, whereas higher efavirenz exposure is predicted to decrease total and unbound concentrations. Conclusions: Simulations suggest that doubling the dose of levonorgestrel, particularly in combination with 400 mg daily efavirenz, may mitigate the drug interaction. Changes in levonorgestrel plasma protein binding and efavirenz genetic polymorphism may help explain differences between model predictions and clinical data but need to be studied further.

Physiologically-based pharmacokinetic modeling of prominent oral contraceptive agents and applications in drug-drug interactions

Considerable interest remains across the pharmaceutical industry and regulatory landscape in capabilities to model oral contraceptives (OCs), whether combined (COCs) with ethinyl estradiol (EE) or progestin-only pill. Acceptance of COC drug-drug interaction (DDI) assessment using physiologically-based pharmacokinetic (PBPK) is often limited to the estrogen component (EE), requiring further verification, with extrapolation from EE to progestins discouraged. There is a paucity of published progestin component PBPK models to support the regulatory DDI guidance for industry to evaluate a new chemical entity's (NCE's) DDI potential with COCs. Guidance recommends a clinical interaction study to be considered if an investigational drug is a weak or moderate inducer, or a moderate/strong inhibitor, of CYP3A4. Therefore, availability of validated OC PBPK models within one software platform, will be useful in predicting the DDI potential with NCEs earlier in the clinical development. Thus, this work was focused on developing and validating PBPK models for progestins, DNG, DRSP, LNG, and NET, within Simcyp, and assessing the DDI potential with known CYP3A4 inhibitors (e.g., ketoconazole) and inducers (e.g., rifampicin) with published clinical data. In addition, this work demonstrated confidence in the Simcyp EE model for regulatory and clinical applications by extensive verification in 70+ clinical PK and CYP3A4 interaction studies. The results provide greater capability to prospectively model clinical CYP3A4 DDI with COCs using Simcyp PBPK to interrogate the regulatory decision-tree to contextualize the potential interaction by known perpetrators and NCEs, enabling model-informed decision making, clinical study designs, and delivering potential alternative COC options for women of childbearing potential.

Clinical pharmacology of progestins

INTRODUCTION

In this paper, we report general pharmacological profile and major biological activities of natural progesterone (P) and progestins. The aim of this article consists of synthesizing the principal aspects of pharmacology and metabolism of P and progestins related to the clinical consequences of their use.

METHODS

We review scientific literature on the topic "Progestins", evaluating the most relevant data from original articles, reviews and meta-analyses.

EVIDENCE SYNTHESIS

Progestins represent a specific class of synthetic analogues of P clinically employed (alone or associated with estrogens) to manage several gynaecological conditions, for instance multiple abortions, luteal phase defect, premenstrual syndrome, abnormal uterine bleeding, endometriosis and menopause (for hormone replacement therapy). Besides their use in the field of contraception, many non-contraceptive benefits of estroprogestins are mostly due to the activities of progestins. Pharmacological characteristics, dosage and individual metabolism could be listed among the principal aspects influencing their clinical effects.

CONCLUSIONS

The choice of each progestin according to its pharmacological profile is crucial for the appropriate management of any gynaecological condition. An aware knowledge of these compounds is fundamental to hone medical practice.

Pharmacokinetics, metabolism and serum concentrations of progestins used in contraception

Many different forms of hormonal contraception are used by millions of women worldwide. These contraceptives differ in the dose and type of synthetic progestogenic compound (progestin) used, as well as the route of administration and whether or not they contain estrogenic compounds. There is an increasing awareness that different forms of contraception and different progestins have different side-effect profiles, in particular their cardiovascular effects, effects on reproductive cancers and susceptibility to infectious diseases. There is a need to develop new methods to suit different needs and with minimal risks, especially in under-resourced areas. This requires a better understanding of the pharmacokinetics, metabolism, serum and tissue concentrations of progestins used in contraception as well as the biological activities of progestins and their metabolites via steroid receptors. Here we review the current knowledge on these topics and identify the research gaps. We show that there is a paucity of research on most of these topics for most progestins. We find that major impediments to clear conclusions on these topics include a lack of standardized methodologies, comparisons between non-parallel clinical studies and variability of data on serum concentrations between and within studies. The latter is most likely due, at least in part, to differences in intrinsic characteristics of participants. The review highlights the importance of insight on these topics in order to provide the best contraceptive options to women with minimal risks.

Risk-Benefit Assessment of Ethinylestradiol Using a Physiologically Based Pharmacokinetic Modeling Approach

Current formulations of combined oral contraceptives (COC) containing ethinylestradiol (EE) have ≤35 μg due to increased risks of cardiovascular diseases (CVD) with higher doses of EE. Low‐dose formulations however, have resulted in increased incidences of breakthrough bleeding and contraceptive failure, particularly when coadministered with inducers of cytochrome P450 enzymes (CYP). The developed physiologically based pharmacokinetic model quantitatively predicted the effect of CYP3A4 inhibition and induction on the pharmacokinetics of EE. The predicted C_max and AUC ratios when coadministered with voriconazole, fluconazole, rifampicin, and carbamazepine were within 1.25 of the observed data. Based on published clinical data, an AUC_ss value of 1,000 pg/ml.h was selected as the threshold for breakthrough bleeding. Prospective application of the model in simulations of different doses of EE (20 μg, 35 μg, and 50 μg) identified percentages of the population at risk of breakthrough bleeding alone and with varying degrees of CYP modulation.

Ethynilestradiol 20 mcg plus Levonorgestrel 100 mcg: Clinical Pharmacology

Estroprogestins (EPs) are combinations of estrogen and progestin with several actions on women's health. The different pharmacological composition of EPs is responsible for different clinical effects. One of the most used low-dose EP associations is ethinylestradiol 20 mcg plus levonorgestrel 100 mcg in monophasic regimen (EE20/LNG100). This review summarizes clinical pharmacology, cycle control, and effects on lipid and glucose metabolism, coagulation, body weight/body composition, acne, and sexuality of EE20/LNG100. Overall, EE20/LNG100 combination is safe and well tolerated, and in several studies the incidence of adverse events in the treated group was comparable to that of the placebo group. Cycle control was effective and body weight/body composition did not vary among treated and untreated groups in most studies. The EE20/LNG100 combination shows mild or no effect on lipid and glucose metabolism. Lastly, EE20/LNG100 is associated with a low risk of venous thromboembolism (VTE). In conclusion, in the process of decision making for the individualization of EPs choice, EE20/LNG100 should be considered for its favorable clinical profile.

A systematic review of effectiveness and safety of different regimens of levonorgestrel oral tablets for emergency contraception

BACKGROUND

Unintended pregnancy is a complex phenomenon which raise to take an emergency decision. Low contraceptive prevalence and high user failure rates are the leading causes of this unexpected situation. High user failure rates suggest the vital role of emergency contraception to prevent unplanned pregnancy. Levonorgestrel - a commonly used progestin for emergency contraception. However, little is known about its pharmacokinetics and optimal dose for use. Hence, there is a need to conduct a systematic review of the available evidences.

METHODS

Randomized, double-blind trials were sought, evaluating healthy women with regular menstrual cycles, who requested emergency contraception within 72 h of unprotected coitus, to one of three regimens: 1.5 mg single dose levonorgestrel, two doses of 0.75 mg levonorgestrel given 12 h apart or two doses of 0.75 mg levonorgestrel given 24 h apart. The primary outcome was unintended pregnancy; other outcomes were side-effects and timing of next menstruation.

RESULTS

Every trial under consideration successfully established the contraceptive effectiveness of levonorgestrel for preventing unintended pregnancy. Moreover, a single dose of levonorgestrel 1.5 mg for emergency contraception supports its safety and efficacy profile. If two doses of levonorgestrel 0.75 mg are intended for administration, the second dose can positively be taken 12-24 h after the first dose without compromising its contraceptive efficacy. The main side effect was frequent menstrual irregularities. No serious adverse events were reported.

CONCLUSIONS

The review shows that, emergency contraceptive regimen of single-dose levonorgestrel is not inferior in efficacy to the two-dose regimen. All the regimens studied were very efficacious for emergency contraception and prevented a high proportion of pregnancies if taken within 72 h of unprotected coitus. Single levonorgestrel dose (1.5 mg) can substitute two 0.75 mg doses 12 or 24 h apart. With either regimen, the earlier the treatment is given, the more effective it seems to be.

Comparing the effects of low-dose contraceptive pills to control dysfunctional uterine bleeding by oral and vaginal methods

Background and Objective: Contraceptive pills are generally taken orally and can cause side effects such as nausea, vomiting and hypertension. The vaginal use of these pills can reduce such complications. Our objective was to compare the efficacy and side effects of low dose contraceptive pills by oral and vaginal route in the management of dysfunctional uterine bleeding-(DUB)

Methods: This comparative observational study was conducted at Beheshti and Alzahra (SA) teaching hospitals, affiliated to Isfahan University of Medical Sciences in 2010-2011. One hundred women who presented with DUB were randomly assigned into two groups of equal number, receiving the low dose oral contraceptive pills by oral or vaginal route for three month. The amount and duration of bleeding were compared at the beginning and at the end of the study and side effects by these two methods compared.

Results: The results of this study showed that both oral and vaginal routes effectively reduced the duration and amount of bleeding due to DUB after three courses of treatment. This effect was better in the vaginal method compared with oral administration (P = 0.03). Regarding the side effects, nausea and vomiting were significantly higher in the oral group than in the vaginal group (P = 0.03). Vulvovaginitis infection was more frequent in the vaginal group than in the oral group (P = 0.03).

Conclusion: Low dose contraceptive pills are effective in reducing the amount, time, and duration of bleeding in patients with DUB. In addition, reduction of gastrointestinal side effects by vaginal route helps to use these pills by the patient with proper training of physicians, midwives and patients.

Sildenafil citrate in the treatment of pain in primary dysmenorrhea: a randomized controlled trial

STUDY QUESTION

Is a vaginal preparation of sildenafil citrate capable of alleviating acute menstrual pain in patients with primary dysmenorrhea (PD)?

SUMMARY ANSWER

A vaginal preparation of sildenafil citrate is capable of alleviating acute menstrual pain in patients with PD with no observed adverse effects.

WHAT IS KNOWN ALREADY

Oral preparations of nitric oxide (NO) donor drugs augment relaxant effects of NO on myometrial cells, reverse the vasoconstriction caused by prostaglandins and successfully alleviate pain, but the incidence of side effects is too high for routine clinical use. Sildenafil citrate inhibits type 5-specific phosphodiesterase (PDE5), thus preventing the degradation of cyclic guanosine monophosphate (cGMP) in the muscle and augmenting the vasodilatory effects of NO. Therefore, by inhibiting PDE5, the tissue remains relaxed and more blood can circulate through. It has been used previously in a vaginal form with no observed side effects, and it enhances endometrial blood flow.

STUDY DESIGN, SIZE, DURATION

A double-blind, randomized, controlled trial comparing vaginal preparation of sildenafil citrate (100 mg single dose) to a placebo in 62 PD patients at the time of painful menstruation was conducted. The primary outcome was total pain relief over 4 consecutive hours (TOPAR4) comparing sildenafil citrate to placebo, where higher TOPAR4 scores represent better pain relief. Secondary outcomes were pain relief as measured by the visual analog scale (VAS) and uterine artery pulsatility index (PI). Subjects were recruited from December 2007 to January 2011. The trial was stopped due to closeout of the funding for the study.

PARTICIPANTS, SETTINGS, METHODS

Participants were women in good health, were aged 18-35 years and suffered from moderate to severe PD. They were randomized to either vaginal placebo or 100 mg vaginal sildenafil citrate in a 1:1 ratio using random permuted blocks having a block size of 4. At baseline and 1, 2, 3, and 4 h post-treatment, patients were asked to provide assessment of their degree of pain using two scales: (i) pain on the 5-level ordinal scale used for TOPAR4 calculation and (ii) pain level on the VAS. The study ended 4 h after treatment initiation.

MAIN RESULTS AND THE ROLE OF CHANCE

Twenty-five subjects completed the study. Using the TOPAR4 score, the sildenafil citrate group had significantly better pain relief compared with the placebo group [mean (SD): 11.9 (3.2) versus 6.4 (2.1), respectively; difference in means = 5.3; 95% CI: (2.9,7.6); P < 0.001)]. On the VAS, sildenafil citrate provided better pain relief than placebo at each time point. At the 2-h time point, the PI was significantly lower in the sildenafil citrate group compared with the placebo group [mean (SD): 1.6 (0.6) versus 2.3 (0.5), respectively; difference in means = -0.7; 95% CI: (-1.2, -0.1); P = 0.01)].

LIMITATIONS, REASONS FOR CAUTION

Since we did not meet our sample size due to the loss of funding and could not confirm our primary hypothesis, larger studies of longer duration, likely multi-center, are needed to confirm the findings from this study.

WIDER IMPLICATIONS OF THE FINDINGS

A number of medications have been investigated to improve the treatment options for PD, but most have proven unsuccessful or to have an unfavorable risk/benefit ratio. Since PD is a condition that most women suffer from and seek treatment for at some point in their lives, our study offers hope that vaginal sildenafil citrate is a safe and effective option for patients who do not desire or are unresponsive to treatments now available on the market.

STUDY FUNDING/COMPETING INTERESTS

Funding for this study was provided by National Institutes of Health (NIH) grants RO3 TW007438 and K24 HD01476. The authors report no relevant conflicts of interest.

TRIAL REGISTRATION NUMBER

NCT00123162 (Clinical trials.gov).

Trigger values for investigation of hormonal activity in drinking water and its sources using CALUX bioassays

To screen for hormonal activity in water samples, highly sensitive in vitro CALUX bioassays are available which allow detection of estrogenic (ERα), androgenic (AR), progestagenic (PR), and glucocorticoid (GR) activities. This paper presents trigger values for the ERα, AR, PR, and GR CALUX bioassays for agonistic hormonal activities in (drinking) water, which define a level above which human health risk cannot be waived a priori and additional examination of specific endocrine activity may be warranted. The trigger values are based on 1) acceptable or tolerable daily intake (ADI/TDI) values of specific compounds, 2) pharmacokinetic factors defining their bioavailability, 3) estimations of the bioavailability of unknown compounds with equivalent hormonal activity, 4) relative endocrine potencies, and 5) physiological, and drinking water allocation factors. As a result, trigger values of 3.8ng 17β-estradiol (E2)-equivalents (eq)/L, 11ng dihydrotestosterone (DHT)-eq/L, 21ng dexamethasone (DEX)-eq/L, and 333ng Org2058-eq/L were derived. Benchmark Quotient (BQ) values were derived by dividing hormonal activity in water samples by the derived trigger using the highest concentrations detected in a recent, limited screening of Dutch water samples, and were in the order of (value) AR (0.41)>ERα (0.13)>GR (0.06)>PR (0.04). The application of trigger values derived in the present study can help to judge measured agonistic hormonal activities in water samples using the CALUX bioassays and help to decide whether further examination of specific endocrine activity followed by a subsequent safety evaluation may be warranted, or whether concentrations of such activity are of low priority with respect to health concerns in the human population. For instance, at one specific drinking water production site ERα and AR (but no GR and PR) activities were detected in drinking water, however, these levels are at least a factor 83 smaller than the respective trigger values, and therefore no human health risks are to be expected from hormonal activity in Dutch drinking water from this site.

Pharmacokinetics of single-dose levonorgestrel in adolescents

PURPOSE

The purpose of this study is to compare the pharmacokinetics of levonorgestrel, a drug used for emergency contraception between female adolescents and adults.

METHODS

Twenty-two female subjects, aged 13-16 years, received a single 0.75-mg dose of the drug. Serial blood samples were collected for 72 h and used to measure plasma levonorgestrel concentrations. Previously published data from 16 adults, aged 18-45 years, served as comparison.

RESULTS

There was a statistically significant higher total plasma clearance divided by the bioavailability (CL/F) of levonorgestrel in adolescents compared to adults, resulting in lower maximum and average total plasma concentrations. There was a trend for a larger volume of distribution divided by bioavailability (V/F), but there was no significant difference in the half-life of levonorgestrel in adolescents relative to adults (p=.098).

CONCLUSION

The differences between adolescents and adults are unlikely to be clinically significant because specific changes in total concentrations suggest that unbound concentrations are probably not affected. Furthermore, empirically high doses of levonorgestrel are given for emergency contraception.

Pharmacology of estrogens and progestogens: influence of different routes of administration

This review comprises the pharmacokinetics and pharmacodynamics of natural and synthetic estrogens and progestogens used in contraception and therapy, with special consideration of hormone replacement therapy. The paper describes the mechanisms of action, the relation between structure and hormonal activity, differences in hormonal pattern and potency, peculiarities in the properties of certain steroids, tissue-specific effects, and the metabolism of the available estrogens and progestogens. The influence of the route of administration on pharmacokinetics, hormonal activity and metabolism is presented, and the effects of oral and transdermal treatment with estrogens on tissues, clinical and serum parameters are compared. The effects of oral, transdermal (patch and gel), intranasal, sublingual, buccal, vaginal, subcutaneous and intramuscular administration of estrogens, as well as of oral, vaginal, transdermal, intranasal, buccal, intramuscular and intrauterine application of progestogens are discussed. The various types of progestogens, their receptor interaction, hormonal pattern and the hormonal activity of certain metabolites are described in detail. The structural formulae, serum concentrations, binding affinities to steroid receptors and serum binding globulins, and the relative potencies of the available estrogens and progestins are presented. Differences in the tissue-specific effects of the various compounds and regimens and their potential implications with the risks and benefits of hormone replacement therapy are discussed.

Bioavailability of the Yuzpe and levonorgestrel regimens of emergency contraception: vaginal vs. oral administration

Separate crossover studies compared the bioavailability of oral vs. vaginal routes of administration for the Yuzpe (n=5) and levonorgestrel regimens (n=4) of emergency contraception. Twice the standard dose of the Yuzpe regimen (200 microg of ethinyl estradiol, 1000 microg of levonorgestrel) or the levonorgestrel regimen (1500 microg of levonorgestrel) was self-administered vaginally. One week later, each subject received orally the standard dose of the assigned medication. Serial blood samples were collected over 24 h and assayed for levonorgestrel and ethinyl estradiol (for the Yuzpe regimen only). Paired t tests were used to compare oral vs. vaginal administration for maximum concentration (Cmax), time to maximum concentration (Tmax) and area under the curve over 24 h (AUC0-24). Relative bioavailability (vaginal/oral) was derived from AUC0-24. Vaginal administration of double the standard dose of the Yuzpe regimen resulted in a lower Cmax (vaginal=5.4 vs. oral=14.6 ng/mL, p=.038) and a later Tmax (5.9 vs. 2.0 h, p=.066) for levonorgestrel, compared to oral administration. Corresponding ethinyl estradiol concentrations were higher (786 vs. 391 pg/mL, p=.039) and peaked later (4.0 vs. 1.9 hr, p=.154) with vaginal administration. Relative bioavailabilities for levonorgestrel and ethinyl estradiol were 58% and 175%, respectively. Similarly, vaginal administration of the levonorgestrel regimen resulted in a lower Cmax (vaginal=5.4 vs. oral=15.2 ng/mL, p=.006) and a later Tmax (7.4 vs. 1.3 h, p=.037) for levonorgestel, compared to oral administration. The relative bioavailability was 62%. Our preliminary data suggest that vaginal administration of these emergency contraception regimens appears to require at least three times the standard oral dose to achieve equivalent systemic levonorgestrel concentrations.

Pharmacokinetics and endometrial tissue levels of levonorgestrel after administration of a single 1.5-mg dose by the oral and vaginal route

OBJECTIVE

To determine the pharmacokinetics and endometrial tissue levels of levonorgestrel when taken as a single dose of 1.5 mg either orally or vaginally by healthy women in the periovulatory phase of their menstrual cycle.

DESIGN

Prospective randomized study.

SETTING

Academic research institution.

PATIENT(S)

Thirty women with regular cycles allocated to control (n = 5), oral (n = 13), and vaginal (n = 12) groups.

INTERVENTION(S)

Blood samples were drawn before (0 time) and at 0.5, 1, 2, 4, 6, 8, 24, 48, and 168 hours after levonorgestrel administration. Endometrial samples were collected 24 and 168 hours after levonorgestrel administration.

MAIN OUTCOME MEASURE(S)

Plasma and endometrial tissue levels of levonorgestrel.

RESULT(S)

Plasma concentrations of levonorgestrel were significantly greater during the first 48 hours after oral administration. However, 7 days after levonorgestrel administration, the plasma levels were similar for both treatments (3-5 nmol/L). Compared with vaginal administration, oral administration resulted in higher peak plasma concentrations (Cmax 64 vs. 10.7 nmol/L), with a shorter time to reach the maximal concentrations (Tmax 1.4 vs. 6.6 hours) and with a greater AUC (509 vs. 175 nmol/L). Interestingly, the half-life of levonorgestrel was shorter after oral administration (25 hours vs. 32.6 hours). Levonorgestrel tissue concentrations were not related to the plasma levels. Levonorgestrel values tended to be higher in endometrial tissue after vaginal administration. The ratio between plasma and endometrial concentrations of levonorgestrel differed significantly between the groups.

CONCLUSION(S)

These data indicate that orally administered levonorgestrel achieves higher plasma levels sooner than vaginally administered levonorgestrel. However, plasma levels after vaginal administration are more sustained and were likely to be sufficient for ovarian suppression. Therefore, the vaginally administered levonorgestrel could be considered as an alternative option for emergency contraception.

Classification of orally administered drugs on the World Health Organization Model list of Essential Medicines according to the biopharmaceutics classification system

Since its inception in 1995, the biopharmaceutical classification system (BCS) has become an increasingly important tool for regulation of drug products world-wide. Until now, application of the BCS has been partially hindered by the lack of a freely available and accurate database summarising solubility and permeability characteristics of drug substances. In this report, orally administered drugs on the Model list of Essential Medicines of the World Health Organization (WHO) are assigned BCS classifications on the basis of data available in the public domain. Of the 130 orally administered drugs on the WHO list, 61 could be classified with certainty. Twenty-one (84%) of these belong to class I (highly soluble, highly permeable), 10 (17%) to class II (poorly soluble, highly permeable), 24 (39%) to class III (highly soluble, poorly permeable) and 6 (10%) to class IV (poorly soluble, poorly permeable). A further 28 drugs could be provisionally assigned, while for 41 drugs insufficient or conflicting data precluded assignment to a specific BCS class. A total of 32 class I drugs (either certain or provisional classification) were identified. These drugs can be further considered for biowaiver status (drug product approval based on dissolution tests rather than bioequivalence studies in humans).

Pharmacokinetics of levonorgestrel 0.75 mg tablets

This study examined plasma levonorgestrel (LNG) concentrations and pharmacokinetics following oral administration of a single LNG 0.75 mg tablet. Sixteen healthy female volunteers 19-44 years old enrolled in the study. Serial blood samples were drawn over 72 h after dosing in a fasting state. A gas chromatographic, negative ionization mass spectrometric detection analytical method was used to determine plasma LNG concentrations. The observed mean peak plasma LNG concentration was 14.1 +/- 7.9 ng/mL (range 6.7-39.0 ng/mL). The mean time of peak concentration was 1.63 +/- 0.74 h (range 1-4 h). The plasma LNG concentration versus time profiles were subjected to noncompartmental pharmacokinetic analysis for the purposes of determining half-lives, apparent oral clearances (Cl/F), apparent volumes of distribution after oral administration (V/F), and mean residence time (MRT). Half-lives calculated from the terminal decline in plasma LNG concentrations ranged from 16.2 h to 32.3 h (mean = 24.4 +/- 5.3 h). The Cl/F was 7.06 +/- 2.69 L/h, V/F was 260 +/- 129 L, and MRT was 27.8 +/- 5.2 h. LNG was well tolerated; there were no serious adverse events during the study.

Bioavailability of orally administered sex steroids used in oral contraception and hormone replacement therapy

The concept of bioavailability is discussed with particular references to the sex steroids. Problems encountered in the measurement of bioavailability of these steroids and the various factors that may affect their bioavailability are briefly described. Information regarding the bioavailability of the estrogens and gestogens, some of which are prodrugs, used in oral contraception and hormone replacement therapy is summarized and the implications regarding the clinical use of these steroids are discussed.

Pharmacokinetics of levonorgestrel and ethinylestradiol in 14 women during three months of treatment with a tri-step combination oral contraceptive: serum protein binding of levonorgestrel and influence of treatment on free and total testosterone levels in the serum

The pharmacokinetics of levonorgestrel (LNG) and ethinylestradiol (EE2) were determined in 14 healthy women (age 18 to 27 years) during a treatment period of three months with a tri-step combination oral contraceptive (Triquilar). Prior to this treatment period, the same women received a single administration of a coated tablet containing 0.125 mg LNG together with 0.03 mg EE2. There was a washout phase of one week between both treatments. Following single dose administration, a mean terminal half-life of 22 h was observed for LNG. The total clearance was 1.0 ml x min-1 x kg-1 and the volume of distribution was 128 l. During a treatment cycle, LNG levels in the serum accumulated by a factor of about four as compared to single dose administration. Steady-state drug levels were reached during the second half of each cycle. As compared to single dose administration, the following changes were observed for LNG at the end of treatment cycles one and three: reduced total (0.5 ml x min-1 x kg-1) and free clearance (50 ml x min-1 x kg-1) and a reduced volume of distribution (52 l). A concomitant increase in the SHBG concentrations by a factor of two as compared to pretreatment values was observed during treatment and appeared to be mainly responsible for the changes in the pharmacokinetics of LNG. Marked changes were also seen for the serum protein binding of LNG. After single dose administration, the free fraction of LNG was 1.4% and the fractions bound to SHBG and albumin were 55.0% and 43.6%, respectively. At the end of cycle one, the free fraction was only 1.0% and the fractions bound to SHBG and albumin were 69.4% and 30.0%, respectively. There was no difference in corresponding pharmacokinetic parameters and in the serum protein binding of LNG at the end of cycles one and three. On the last day of treatment cycles one and three, the AUC(0-4h) values of EE2 were 331.2 and 369.6 pg x ml-1 x h, respectively, which corresponds to an about 11-24% increase as compared to single dose administration, where an AUC(0-4h) value of 298.3 pg x ml-1 x h was found. Total and free testosterone concentrations decreased during treatment cycles one and three by about 41% and 55%, respectively, compared with the corresponding values measured prior to treatment.

Pharmacokinetics of levonorgestrel in 12 women who received a single oral dose of 0.15 mg levonorgestrel and, after a washout phase, the same dose during one treatment cycle

The pharmacokinetics of levonorgestrel (LNG) was determined in 12 healthy women (age 21 to 33 years), following single dose administration of 0.15 mg LNG. The same preparation was also administered during one treatment cycle after a washout phase of 1 week. After single dose administration, maximum concentrations of LNG in the serum were 4.3 +/- 1.3 ng/ml. Post maximum drug levels declined biphasically with half-lives of 0.6 +/- 0.2 h and 13.9 +/- 3.2 h, respectively. The clearance was calculated to be 1.5 +/- 0.6 ml x min-1 x kg-1. The free fraction of LNG was 1.1 +/- 0.1% and the fractions bound to SHBG and albumin were 61.8 +/- 6.7% and 37.1 +/- 6.7%, respectively. There was a gradual decrease in serum trough levels of LNG from about 0.5 to 0.3 ng/ml during the cycle, and a concomitant decrease in SHBG concentrations in the serum by about 50%. Serum protein binding of LNG changed markedly during the treatment cycle. The free fraction increased to a value of 1.7 +/- 0.3%, the SHBG-bound fraction decreased to 42.0 +/- 11.4% and the albumin-bound fraction increased to 56.4 +/- 11.2%. Total serum clearance increased during the same time period from a mean value of 1.5 to about 2.5 ml x min-1 x kg-1. The clearance of unbound LNG, however, remained unchanged. An examination of the free LNG concentrations revealed the same time course of LNG trough levels during the cycle as the simulated curve. This was derived from the pharmacokinetic parameters which were obtained after single dose administration. Thus, the present study showed that the pharmacokinetics of LNG can be fully explained on the basis of single dose pharmacokinetics and the changes in serum protein binding which were caused by a reduction of SHBG levels in the serum during chronic treatment with LNG.

Pharmacokinetics of levonorgestrel and ethinylestradiol in 9 women who received a low-dose oral contraceptive over a treatment period of 3 months and, after a wash-out phase, a single oral administration of the same contraceptive formulation

The pharmacokinetics of levonorgestrel (LNG) and ethinylestradiol (EE2) were determined in 9 healthy women (age 23 to 42 years), during a treatment period of three months with a low-dose oral contraceptive, containing 0.15 mg LNG together with 0.03 mg EE2 (Microgynon). After a wash-out period of 3 months, 8 of these women received a single administration of the same formulation. The results showed that there was an increase in serum trough levels of LNG, reaching steady-state in the second half of each treatment cycle. The LNG levels achieved were about 3 to 4 times higher than anticipated on the basis of single dose administration. At the end of treatment cycles one and three, the terminal half-life of LNG was in the range of 24-26 h, while a mean value of 20 h was observed following single dose administration. An EE2-induced increase in the SHBG concentration of about 50% as compared to pretreatment values was observed during a treatment cycle. Pretreatment values were reached following the drug-free interval of 7 days between two cycles. After single dose administration, the free fraction of LNG was 1.3 +/- 0.2% and the fractions bound to SHBG and albumin were 64.1 +/- 4.2% and 34.6 +/- 4.0%, respectively. Serum protein binding of LNG did not change during chronic treatment. An about 50% reduction in total and unbound clearance of LNG was observed during chronic treatment, as compared to single dose administration. Increased SHBG binding capacity and a reduced hepatic metabolic capacity were discussed as possible causes of accumulating LNG concentrations in the serum. On the last day of treatment cycles one and three, the AUC(0-24h) values of EE2 were 728 +/- 314 and 778 +/- 318 pg x ml-1 x h, respectively, and were in keeping with data reported from others.

Pharmacokinetics and pharmacodynamics of oral contraceptive steroids: factors influencing steroid metabolism

The time-dependent alterations in the serum concentrations of ethinyl estradiol, gestodene, and 3-keto-desogestrel during treatment with 30 micrograms of ethinyl estradiol + 75 micrograms of gestodene or 30 micrograms of ethinyl estradiol + 150 micrograms of desogestrel were investigated during 12 months. The levels of gestodene and 3-keto-desogestrel increased between days 1 and 21 of each cycle, reaching maximal levels during the third and sixth cycles. The serum concentrations of gestodene were fourfold to fivefold higher than those of 3-keto-desogestrel. The ethinyl estradiol levels increased significantly between days 1 and 10 during each cycle and were significantly higher by 70% during intake of ethinyl estradiol/gestodene compared with ethinyl estradiol/desogestrel, although the dose was identical. Intake of gestodene, in addition to 35 micrograms of ethinyl estradiol + 2 mg of cyproterone acetate, caused a rise in ethinyl estradiol levels. During treatment with ethinyl estradiol/gestodene and an additional 150 micrograms of levonorgestrel, there was a continuous increase in gestodene levels, although sex hormone-binding globulin level did not change. During treatment with 30 or 35 micrograms of ethinyl estradiol and 75 micrograms of gestodene, 150 micrograms of desogestrel, or 2 mg of cyproterone acetate, there were large intraindividual and interindividual variations in the steroid levels and ratios of estrogen: progestogen levels. There was no correlation with the occurrence of intermenstrual bleedings. It is concluded that ethinyl estradiol and nortestosterone derivatives may inhibit steroid-metabolizing enzymes in the liver, which results in a rise in the serum levels of contraceptive steroids. The cause of the large intraindividual variations is as yet unknown, but it is probably from changes in steroid metabolism.

Pharmacokinetics of gestagens: some problems

Various approaches to studying the pharmacokinetics of gestagens and the factors that influence derivation of the parameters are described with levonorgestrel used as an example. Published studies of the pharmacokinetics of levonorgestrel are reviewed, and new information is presented regarding intra- and intersubject variation. Differences between various formulations of levonorgestrel are apparent when the formulations are compared in the same subjects. There is also a marked difference in the parameters when derived under single-dose or steady-state conditions. The role of sex hormone-binding globulin in the metabolism of levonorgestrel is questioned. Large intra- and inter-subject variations in the parameters exist, and a subject may show a large month-to-month variation when one levonorgestrel formulation is used and smaller variations when another formulation is used. This wide variability in the pharmacokinetic parameters, problems that arise in the derivation and interpretation of the parameters, the biologic significance of most of these parameters, and their lack of correlation with pharmacodynamic responses severely limit the usefulness of pharmacokinetic studies of the gestagens.

Potency and pharmacokinetics of gestagens

Serum concentrations of gestagens were compared after single doses and after multiple doses (steady-state conditions) of four widely used oral contraceptives containing norethisterone (NET), levonorgestrel (LNG), desogestrel (DSG) and gestodene (GSD). There were marked differences among the gestagens with respect to the serum concentrations. Under steady-state conditions 12 h after dosing, the relative concentrations were approximately GSD, 4.5:DSG, 1:LNG, 1:NET, 2 compared to ratios of 1:2:2:13.3, respectively, for dose. Thus, there was no correlation between serum concentration and dose. These differences in serum concentrations are determined by the different pharmacokinetic behaviour of the gestagens, which in turn is largely determined by their binding to serum proteins. Calculations suggest that the concentrations of unbound gestagen in serum, and hence probably also at the target organ, are similar (about 35 pg/ml) for LNG, DSG and GSD but may be higher (up to 60 pg/ml) for NET whose half-life of elimination is about half that of the other three gestagens. Measurement of the serum total concentration is unlikely to correlate with their pharmacological activity. A further complication is the multiplicity of pharmacological effects elicited by the gestagens and each of these effects is likely to have its own dose-response relationship.

Transdermal dual-controlled delivery of contraceptive drugs: formulation development, in vitro and in vivo evaluations, and clinical performance

Several transdermal contraceptive device (TCD) formulations were developed to provide a dual-controlled transdermal delivery of levonorgestrel (LN), a potent progestin, and 17 beta-estradiol (E2), a natural estrogen. Using a sensitive HPLC method, the in vitro release and skin permeation profiles of LN and E2 from various TCD formulations were simultaneously characterized in the hydrodynamically well-calibrated Valia-Chien skin permeation cells and both were found to follow zero-order kinetics. The rates of drug release and skin permeation were observed to vary significantly depending upon some formulation parameters. Six-month stability studies were performed on seven formulations at room and elevated temperatures (37 and 45 degrees C), and two (Formulations 4 and 5) were found to be acceptable, based on drug recovery, release rate, and skin permeation rate data. Judging from the 6-month accelerated stability studies, it is projected these two formulations will have shelf-life of at least 2 years. As a result of development of an efficient manufacturing process, Formulation 4 was selected for further evaluation. One-week primary skin irritation evaluation in 6 rabbits indicated that Formulation 4 is nonirritating, and it was thus selected for Phase I clinical bioavailability/dose proportionality studies in 12 healthy female volunteers of child-bearing age. Results of pharmacokinetic and pharmacodynamic analyses demonstrated that it is capable of achieving and maintaining a steady-state serum level of LN throughout the 3-week treatment period by weekly applications of one or two TCD patches (10 or 20 cm2). A dose proportionality was obtained in the serum drug levels, daily dose delivered, and contraception efficacy. An excellent correlation was obtained for the rates of transdermal delivery determined by the in vitro studies using human cadaver skin, the in vivo studies in rabbits, and the clinical studies in living subjects.

Single dose pharmacokinetics of gestodene in women after intravenous and oral administration

Six healthy female volunteers (age 25 - 39 years) received 75 micrograms gestodene intravenously followed by 3 oral administrations of 25, 75 and 125 micrograms gestodene together with 30 micrograms ethinylestradiol (EE2) in a cross-over design. Gestodene plasma levels were determined using a specific RIA. After intravenous administration, plasma gestodene concentrations decayed triphasically with mean half-lives of 0.16 h, 1.5 h and 10 hours. The area under the plasma level curve, the total plasma clearance and the volume of distribution (VZ) were as follows: AUC = 35 +/- 15 ng.h/ml, CL = 0.80 +/- 0.53 ml/min/kg, and VZ = 0.66 +/- 0.43 1/kg, respectively. After oral administration of all doses, maximum plasma levels of 1.0 (25 micrograms), 3.8 (75 micrograms) and 7.0 ng/ml (125 micrograms) were achieved between 1.4 and 1.9 hours after the intake. Post-maximum levels showed 2 disposition phases with half-lives of 1 and 12 - 14 hours. Absolute bioavailabilities were calculated as 87.5 +/- 17.5% (25 micrograms), 99.3 +/- 10.9% (75 micrograms) and 110.8 +/- 17.7% (125 micrograms) indicating that gestodene is completely absorbed and systemically available at all doses investigated.