PLAN B ONE-STEP
Clinical safety rating: caution
Comprehensive clinical and safety monograph for PLAN B ONE-STEP (PLAN B ONE-STEP).
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.
| Metabolism | Metabolized via reduction, hydroxylation, and conjugation, primarily by CYP3A4. Metabolites are excreted as glucuronide conjugates. |
| Excretion | Renal (approximately 50%), with fecal elimination accounting for the remainder. Metabolites are excreted primarily in urine as glucuronide conjugates. |
| Half-life | Terminal elimination half-life is approximately 24 hours (range 16-32 hours) for levonorgestrel. This supports single-dose administration for emergency contraception. |
| Protein binding | Approximately 97-99% bound to sex hormone-binding globulin (SHBG) and albumin. |
| Volume of Distribution | Approximately 1.8 L/kg, indicating extensive tissue distribution. |
| Bioavailability | Oral: Approximately 100% (virtually complete absorption; first-pass metabolism minimal). |
| Onset of Action | Oral: Maximal contraceptive effect if taken within 72 hours of unprotected intercourse; time to inhibition of ovulation is 24-48 hours. |
| Duration of Action | Single-dose efficacy covers the immediate post-ovulatory period; no prolonged effect. Repeat dosing required for subsequent acts. |
One 1.5 mg tablet orally as a single dose within 72 hours of unprotected intercourse.
| Dosage form | TABLET |
| Renal impairment | No dosage adjustment required for renal impairment. |
| Liver impairment | No dosage adjustment recommended; manufacturer advises caution in severe hepatic impairment (Child-Pugh class C) due to altered hormone metabolism. |
| Pediatric use | For females of reproductive age (post-menarche): same as adult dose (1.5 mg orally once). No weight-based adjustment needed. |
| Geriatric use | Not indicated for postmenopausal women; no specific recommendations for geriatric use as efficacy is limited to premenopausal females. |
| 1st trimester | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
Comprehensive clinical and safety monograph for PLAN B ONE-STEP (PLAN B ONE-STEP).
| Breastfeeding | Levonorgestrel is excreted in breast milk in small amounts; M/P ratio not established. Considered compatible with breastfeeding; no adverse effects reported. Milk transfer minimal due to short half-life. |
| Teratogenic Risk | FDA Pregnancy Category X for routine use; no increased risk of major malformations when used as emergency contraception before pregnancy is established. If pregnancy occurs after use, no evidence of teratogenicity from inadvertent exposure in early gestation. |
| Fetal Monitoring |
■ FDA Black Box Warning
No FDA boxed warning exists for Plan B One-Step.
| Serious Effects |
["Known or suspected pregnancy","Hypersensitivity to any component of the product"]
| Precautions | ["Not intended for routine use as contraception","Reduced efficacy in patients with BMI > 25 kg/m^2; not recommended for BMI > 30 kg/m^2","May cause ectopic pregnancy (suspect in cases of lower abdominal pain, especially if amenorrhea persists after treatment)","Consider possibility of ectopic pregnancy if menstrual period is delayed >7 days","Not effective if already pregnant","Potential for drug interactions with CYP3A4 inducers (e.g., rifampin, anticonvulsants, St. John's wort)"] |
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| No specific monitoring required. If pregnancy occurs after use, standard prenatal care. Monitor for ectopic pregnancy if severe abdominal pain occurs. |
| Fertility Effects | No long-term effects on fertility. Delays ovulation and may cause transient menstrual irregularities, but normal fertility resumes after one menstrual cycle upon discontinuation. |