Tilia Fe

ORAL CONTRACEPTION

Combination oral contraceptives act by suppression of gonadotropins. Although the primary mechanism of this action is inhibition of ovulation, other alterations include changes in the cervical mucus (which increase the difficulty of sperm entry into the uterus) and the endometrium (which reduce the likelihood of implantation).

In vitro and animal studies have shown that norethindrone combines high progestational activity with low intrinsic androgenicity. In humans, norethindrone acetate in combination with ethinyl estradiol does not counteract estrogen-induced increases in sex hormone binding globulin (SHBG). Following multiple-dose administration of Tilia FE, serum SHBG concentrations increase two- to three-fold and free testosterone concentrations decrease by 47% to 64%, indicating minimal androgenic activity.

ACNE

Acne is a skin condition with a multifactorial etiology, including androgen stimulation of sebum production. While the combination of norethindrone acetate and ethinyl estradiol increases sex hormone binding globulin (SHBG) and decreases free testosterone, the relationship between these changes and a decrease in the severity of facial acne in otherwise healthy women with this skin condition has not been established.

Pharmacokinetics

Absorption

Norethindrone acetate appears to be completely and rapidly deacetylated to norethindrone after oral administration, since the disposition of norethindrone acetate is indistinguishable from that of orally administered norethindrone. Norethindrone acetate and ethinyl estradiol are rapidly absorbed, with maximum plasma concentrations of norethindrone and ethinyl estradiol occurring 1 to 2 hours post-dose. 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.

Administration of norethindrone acetate/ethinyl estradiol with a high fat meal decreases rate, but not extent, of ethinyl estradiol absorption. The extent of norethindrone absorption is increased by 27% following administration with food.

Plasma concentrations of norethindrone and ethinyl estradiol following chronic administration of Tilia FE to 17 women are shown below (Figure 1). Mean steady-state concentrations of norethindrone for the 1/20, 1/30, and 1/35 tablet strengths increased as ethinyl estradiol dose increased over the 21-day dose regimen, due to dose-dependent effects of ethinyl estradiol on serum SHBG concentrations (Table 1). Mean steady-state plasma concentrations of ethinyl estradiol for the 1/20, 1/30, and 1/35 tablet strengths were proportional to ethinyl estradiol dose (Table 1).

Figure 1. Mean Steady-State Plasma Ethinyl Estradiol and Norethindrone Concentrations Following Chronic Administration of Tilia FE

*  Cmax = Maximum plasma concentration; AUC (0-24) = Area under the plasma concentration-time curve over the dosing interval; CL/F = Apparent oral clearance
†  Mean (SD) baseline value = 55 (29) nmol/L

No age-related differences were seen in plasma concentrations of ethinyl estradiol and norethindrone following administration of Tilia FE to 119 postmenarchal women ages 15 to 48 years.

Distribution

Volume of distribution of norethindrone and ethinyl estradiol ranges from 2 to 4 L/kg. Plasma protein binding of both steroids is extensive (>95%); norethindrone binds to both albumin and sex hormone binding globulin, whereas ethinyl estradiol binds only to albumin. Although ethinyl estradiol does not bind to SHBG, it induces SHBG synthesis. Tilia FE increases serum SHBG concentrations two- to three-fold (Table 1).

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. A small amount of norethindrone acetate is metabolically converted to ethinyl estradiol. 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 Tilia FE are approximately 13 hours and 19 hours, respectively.

Special Population

Race:

The effect of race on the disposition of Tilia FE has not been evaluated.

Renal Insufficiency

The effect of renal disease on the disposition of Tilia FE has not been evaluated. In premenopausal women with chronic renal failure undergoing peritoneal dialysis who received multiple doses of an oral contraceptive containing ethinyl estradiol and norethindrone, plasma ethinyl estradiol concentrations were higher and norethindrone concentrations were unchanged compared to concentrations in premenopausal women with normal renal function.

Hepatic Insufficiency

The effect of hepatic disease on the disposition of Tilia FE has not been evaluated. However, ethinyl estradiol and norethindrone may be poorly metabolized in patients with impaired liver function.

Drug-Drug Interactions

Numerous drug-drug interactions have been reported for oral contraceptives. A summary of these is found under PRECAUTIONS, Drug Interactions.

Oral contraceptives should not be used in women who currently have the following conditions:

• Thrombophlebitis or thromboembolic disorders
  
• A past history of deep vein thrombophlebitis or thromboembolic disorders
  
• Cerebral vascular or coronary artery disease
  
• Known or suspected carcinoma of the breast
  
• Carcinoma of the endometrium or other known or suspected estrogen-dependent neoplasia
  
• Undiagnosed abnormal genital bleeding
  
• Cholestatic jaundice of pregnancy or jaundice with prior pill use
  
• Hepatic adenomas or carcinomas
  
• Known or suspected pregnancy