Tri Femynor (Page 5 of 9)

12 CLINICAL PHARMACOLOGY

12.1 Mechanism of Action

  • Oral Contraception

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.

  • Acne

Acne is a skin condition with a multifactorial etiology, including androgen stimulation of sebum production. While the combination of ethinyl estradiol and norgestimate 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.

12.2 Pharmacodynamics

No specific pharmacodynamic studies were conducted with Tri Femynor.

12.3 Pharmacokinetics

Absorption

Norgestimate (NGM) and EE are rapidly absorbed following oral administration. NGM is rapidly and completely metabolized by first pass (intestinal and/or hepatic) mechanisms to norelgestromin (NGMN) and norgestrel (NG), which are the major active metabolites of norgestimate.

Peak serum concentrations of NGMN and EE are generally reached by 2 hours after administration of Tri Femynor. Accumulation following multiple dosing of the 250 mcg NGM / 35 mcg EE dose is approximately 2-fold for NGMN and EE compared with single dose administration. The pharmacokinetics of NGMN is dose-proportional following NGM doses of 180 mcg to 250 mcg. Steady-state concentration of EE is achieved by Day 7 of each dosing cycle. Steady-state concentrations of NGMN and NG are achieved by Day 21. Non-linear accumulation (approximately 8 fold) of NG is observed as a result of high-affinity binding to SHBG, which limits its biological activity (Table 3).

Table 3: Summary of NGMN, NG and EE pharmacokinetic parameters.

Mean (SD) Pharmacokinetic Parameters of Tri Femynor During a Three Cycle Study

Analyte

Cycle

Day

Cmax

tmax (h)

AUC0-24h

t1/2 (h)

NGMN

3

7

1.80 (0.46)

1.42 (0.73)

15.0 (3.88)

NC

14

2.12 (0.56)

1.21 (0.26)

16.1 (4.97)

NC

21

2.66 (0.47)

1.29 (0.26)

21.4 (3.46)

22.3 (6.54)

NG

3

7

1.94 (0.82)

3.15 (4.05)

34.8 (16.5)

NC

14

3.00 (1.04)

2.21 (2.03)

55.2 (23.5)

NC

21

3.66 (1.15)

2.58 (2.97)

69.3 (23.8)

40.2 (15.4)

EE

3

7

124 (39.5)

1.27 (0.26)

1130 (420)

NC

14

128 (38.4)

1.32 (0.25)

1130 (324)

NC

21

126 (34.7)

1.31 (0.56)

1090 (359)

15.9 (4.39)

Cmax = peak serum concentration, tmax = time to reach peak serum concentration, AUC0–24h = area under serum concentration vs time curve from 0 to 24 hours, t1/2 = elimination half-life, NC = not calculated.

NGMN and NG: Cmax = ng/mL, AUC0–24h = h·ng/mL

EE: Cmax = pg/mL, AUC0-24h = h·pg/mL

Food Effect

The effect of food on the pharmacokinetics of Tri Femynor has not been studied.

Distribution

NGMN and NG are highly bound (>97%) to serum proteins. NGMN is bound to albumin and not to SHBG, while NG is bound primarily to SHBG. EE is extensively bound (>97%) to serum albumin and induces an increase in the serum concentrations of SHBG.

Metabolism

NGM is extensively metabolized by first-pass mechanisms in the gastrointestinal tract and/or liver. NGM’s primary active metabolite is NGMN. Subsequent hepatic metabolism of NGMN occurs and metabolites include NG, which is also active, and various hydroxylated and conjugated metabolites. Although NGMN and its metabolites inhibit a variety of P450 enzymes in human liver microsomes, under the recommended dosing regimen, the in vivo concentrations of NGMN and its metabolites, even at the peak serum levels, are relatively low compared to the inhibitory constant (Ki). EE is also metabolized to various hydroxylated products and their glucuronide and sulfate conjugates.

Excretion

The metabolites of NGMN and EE are eliminated by renal and fecal pathways. Following administration of 14 C-norgestimate, 47% (45–49%) and 37% (16–49%) of the administered radioactivity was eliminated in the urine and feces, respectively. Unchanged NGM was not detected in the urine. In addition to 17-deacetyl norgestimate, a number of metabolites of NGM have been identified in human urine following administration of radiolabeled NGM. These include 18, 19-Dinor-17-pregn-4-en-20-yn-3-one,17-hydroxy-13-ethyl,(17α)-(-);18,19-Dinor-5β-17-pregnan-20-yn,3α,17β-dihydroxy-13-ethyl,(17α), various hydroxylated metabolites and conjugates of these metabolites.

13 NONCLINICAL TOXICOLOGY

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