Comparative Pharmacology
Head-to-head clinical analysis: LYBREL versus NORTREL 1 35 21.
Peer-Reviewed Evidence
Head-to-head clinical analysis: LYBREL versus NORTREL 1 35 21.
LYBREL vs NORTREL 1/35-21
Comparing the clinical profiles, pharmacokinetic behaviors, and safety indices of these two therapeutic agents.
Combination of levonorgestrel and ethinyl estradiol: suppression of gonadotropins (FSH and LH) via negative feedback, inhibiting ovulation; thickening of cervical mucus to impede sperm penetration; alteration of endometrium to reduce implantation likelihood.
Combination of ethinyl estradiol (estrogen) and norethindrone (progestin) suppresses gonadotropin (FSH and LH) release from the pituitary, inhibiting ovulation, altering cervical mucus to impede sperm penetration, and inducing endometrial changes that reduce implantation likelihood.
One tablet (levonorgestrel 0.1 mg/ethinyl estradiol 0.02 mg) orally once daily for 21 days, followed by 7 placebo tablets for 28-day cycle.
One tablet orally once daily for 21 days, followed by 7 days off, then repeat.
None Documented
None Documented
Terminal elimination half-life: 27 ± 8 hours; requires ~5 days to reach steady-state; clinical significance: missed doses lead to rapid loss of contraceptive efficacy.
Norethindrone: 5-14 hours; Ethinyl estradiol: 17-24 hours. Steady-state achieved after 10 days.
Renal: 50-60% as metabolites, ~20% as parent drug; fecal: 30-40%; biliary: 10-20%.
Renal 50-60% as metabolites, fecal 40-50% as conjugates, <1% unchanged
Category C
Category C
Oral Contraceptive
Oral Contraceptive