Absorption
In a single-dose, two-way, crossover clinical study conducted in 35 healthy, non-smoking premenopausal women under fasting condition, Melodetta 24 Fe tablet chewed and swallowed was bioequivalent to norethindrone acetate 1 mg/ethinyl estradiol 0.020 mg tablet (24-day regimen tablets) swallowed whole based on the exposure (AUC) and peak concentration (Cmax) of norethindrone and ethinyl estradiol.
Norethindrone acetate appears to be completely and rapidly deacetylated to norethindrone after oral administration, because the disposition of norethindrone acetate is indistinguishable from that of orally administered norethindrone. Norethindrone acetate and ethinyl estradiol are absorbed from Melodetta 24 Fe tablets (chewed and swallowed), with maximum plasma concentrations of norethindrone and ethinyl estradiol occurring at 1 hr (range: 0.7 to 2.5 hrs) and 1.3 hr (range: 1 to 2.5 hrs) post-dose, respectively. Both are subject to first-pass metabolism after oral dosing, resulting in an absolute bioavailability of approximately 64% for norethindrone and 43% for ethinyl estradiol.
The plasma norethindrone and ethinyl estradiol pharmacokinetics following single-dose administrations of Melodetta 24 Fe tablets (chewed and swallowed) in 35 healthy female subjects are provided in Figures 1 and 2, and Table 1.
Following multiple-dose administration of norethindrone acetate/ethinyl estradiol tablets (swallowed whole) in 17 healthy female subjects, mean maximum concentrations of norethindrone and ethinyl estradiol were increased by 95% and 27%, respectively, as compared to single-dose administration. Mean norethindrone and ethinyl estradiol exposures (AUC values) were increased by 164% and 51% respectively, as compared to single-dose administration of norethindrone acetate/ethinyl estradiol tablets.
Steady-state with respect to norethindrone was reached by Day 17 and steady-state with respect to ethinyl estradiol was reached by Day 13.
Mean SHBG concentrations were increased by 150% from baseline (57.5 nmol/L) to 144 nmol/L at steady-state.
Figure 1. Mean (± Standard Deviation) Plasma Norethindrone Concentration-Time Profile Following Single-Dose Oral Administration of Melodetta 24 Fe Tablets (chewed and swallowed) to Healthy Female Volunteers under Fasting Conditions (n = 35)
Figure 1 (Melodetta 24 Fe 3)
Figure 2. Mean (± Standard Deviation) Plasma Ethinyl Estradiol Concentration-Time Profile Following Single-Dose Oral Administration of Melodetta 24 Fe Tablets(chewed and swallowed) to Healthy Female Volunteers under Fasting Conditions (n = 35)
Figure 2 (Melodetta 24 Fe 4)
Table 1. Summary of Norethindrone (NE) and Ethinyl Estradiol (EE) Pharmacokinetics Following Single-Dose Oral Administration of Melodetta 24 Fe Tablets (chewed and swallowed) to Healthy Female Volunteers Under Fasting Conditions (n = 35)
Analyte | Arithmetic Meana (% CV) by Pharmacokinetic Parameter |
Cmax (pg/mL) | tmax (hr) | AUC(0−tldc) (pg/mL•h) | AUC(0−inf) (pg/mL•h) | t½ (hr) |
NE | 10200 (36) | 1.03 (0.67 to 2.50) | 48620 (40) | 49250 (40) | 8.58 |
EE | 84.7 (24) | 1.33 (1 to 2.50) | 677.5 (33) | 741.6 (33) | 9.68 |
Cmax = Maximum plasma concentration
tmax = Time of Cmax
AUC(0−tldc) = Area under plasma concentration versus time curve from 0 to tldc, the time of
last determinable concentration
AUC(0−inf) = Area under the plasma concentration versus time curve from time 0 to infinity
t½ = Terminal phase half-life
% CV = Coefficient of Variation (%)
a The harmonic mean (0.693/mean terminal phase rate constant) is reported for t½, and the
median (range) is reported for tmax
Food Effect
Melodetta 24 Fe tablets may be administered without regard to meals.
A single-dose administration of norethindrone acetate/ethinyl estradiol tablets with food decreased the maximum concentration of norethindrone by 51% and increased the extent of absorption by 15% and decreased the maximum concentration of ethinyl estradiol by 51% but not the extent of absorption.
Distribution
Volume of distribution of norethindrone and ethinyl estradiol ranges from 2 to 4 L/kg. Plasma protein binding of both steroids is extensive (greater than 95%); norethindrone binds to both albumin and SHBG, whereas ethinyl estradiol binds only to albumin. Although ethinyl estradiol does not bind to SHBG, it induces SHBG synthesis.
Metabolism
Norethindrone undergoes extensive biotransformation, primarily via reduction, followed by sulfate and glucuronide conjugation. The majority of metabolites in the circulation are sulfates, with glucuronides accounting for most of the urinary metabolites.
Ethinyl estradiol is also extensively metabolized, both by oxidation and by conjugation with sulfate and glucuronide. Sulfates are the major circulating conjugates of ethinyl estradiol and glucuronides predominate in urine. The primary oxidative metabolite is 2-hydroxy ethinyl estradiol, formed by the CYP3A4 isoform of cytochrome P450. Part of the first-pass metabolism of ethinyl estradiol is believed to occur in gastrointestinal mucosa. Ethinyl estradiol may undergo enterohepatic circulation.
Excretion
Norethindrone and ethinyl estradiol are excreted in both urine and feces, primarily as metabolites. Plasma clearance values for norethindrone and ethinyl estradiol are similar (approximately 0.4 L/hr/kg). Steady-state elimination half-lives of norethindrone and ethinyl estradiol following administration of norethindrone acetate/ethinyl estradiol tablets are approximately 8 hours and 14 hours, respectively.