Comparative Pharmacology
Head-to-head clinical analysis: PLAN B versus PREVIFEM.
Peer-Reviewed Evidence
Head-to-head clinical analysis: PLAN B versus PREVIFEM.
PLAN B vs PREVIFEM
Comparing the clinical profiles, pharmacokinetic behaviors, and safety indices of these two therapeutic agents.
Levonorgestrel, a progestin, prevents pregnancy primarily by inhibiting ovulation and altering cervical mucus to impede sperm penetration. It may also inhibit 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 (levonorgestrel) orally as a single dose, taken as soon as possible 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: 24-30 hours. Clinical context: The prolonged half-life supports single-dose regimen for emergency contraception; may be affected by obesity (shorter half-life in obese women).
20-24 hours; steady-state reached in 5 days
Renal (approximately 50% as unchanged drug and metabolites); fecal (approximately 40% as metabolites); less than 1% biliary.
Renal (60% as metabolites, <10% unchanged), fecal (30%), biliary (10%)
Category C
Category C
Emergency Contraceptive
Emergency Contraceptive