Comparative Pharmacology
Head-to-head clinical analysis: PLAN B ONE STEP versus PREVIFEM.
Peer-Reviewed Evidence
Head-to-head clinical analysis: PLAN B ONE STEP versus PREVIFEM.
PLAN B ONE-STEP vs PREVIFEM
Comparing the clinical profiles, pharmacokinetic behaviors, and safety indices of these two therapeutic agents.
Levonorgestrel is a progestin that prevents pregnancy primarily by inhibiting ovulation and altering cervical mucus to impede sperm penetration. It may also interfere with fertilization and implantation.
PREVIFEM is a combination of ethinyl estradiol, an estrogen, and norgestimate, a progestin. It inhibits ovulation by suppressing gonadotropin release from the pituitary (FSH and LH). Additionally, it increases viscosity of cervical mucus, impeding sperm penetration, and alters the endometrium.
One 1.5 mg tablet orally as a single dose within 72 hours of unprotected intercourse.
One tablet (0.075 mg norgestrel and 0.03 mg ethinyl estradiol) orally once daily at the same time each day for 21 consecutive days, followed by 7 placebo tablets.
None Documented
None Documented
Terminal elimination half-life is approximately 24 hours (range 16-32 hours) for levonorgestrel. This supports single-dose administration for emergency contraception.
20-24 hours; steady-state reached in 5 days
Renal (approximately 50%), with fecal elimination accounting for the remainder. Metabolites are excreted primarily in urine as glucuronide conjugates.
Renal (60% as metabolites, <10% unchanged), fecal (30%), biliary (10%)
Category C
Category C
Emergency Contraceptive
Emergency Contraceptive