Plan B One-Step
"Despite the potential for adverse maternal and fetal outcomes, contraceptive use in women with certain medical conditions is suboptimal, according to a new study.
Steven W. Champaloux, PhD, MPH, a scientist in the Division of Reproduc"...
Plan B One-Step
Mechanism of Action
Emergency contraceptive pills are not effective if a woman is already pregnant. Plan B One-Step (levonorgestrel tablet) is believed to act as an emergency contraceptive principally by preventing ovulation or fertilization (by altering tubal transport of sperm and/or ova). In addition, it may inhibit implantation (by altering the endometrium). It is not effective once the process of implantation has begun.
Following a single dose administration of Plan B One-Step (levonorgestrel tablet) in 30 women under fasting conditions, maximum plasma concentrations of levonorgestrel of 19.1 ng/mL were reached at 1.7 hours. See Table 2.
Table 2 : Pharmacokinetic Parameter Values Following Single
Dose Administration of Plan B One-Step (levonorgestrel) tablet 1.5 mg to 30
Healthy Female Volunteers under Fasting Conditions
|Mean ± SD|
|Cmax = maximum concentration
AUCτ = area under the drug concentration curve from time 0 to time of last determinable concentration
AUCinf = area under the drug concentration curve from time 0 to infinity
Tmax = time to maximum concentration
t½ = elimination half life
Effect of Food: The effect of food on the rate and the extent of levonorgestrel absorption following single oral administration of Plan B One-Step (levonorgestrel tablet) has not been evaluated.
The apparent volume of distribution of levonorgestrel is reported to be approximately 1.8 L/kg. It is about 97.5 to 99% protein-bound, principally to sex hormone binding globulin (SHBG) and, to a lesser extent, serum albumin.
Following absorption, levonorgestrel is conjugated at the 17β-OH position to form sulfate conjugates and, to a lesser extent, glucuronide conjugates in plasma. Significant amounts of conjugated and unconjugated 3α, 5β-tetrahydrolevonorgestrel are also present in plasma, along with much smaller amounts of 3α, 5αtetrahydrolevonorgestrel and 16βhydroxylevonorgestrel. Levonorgestrel and its phase I metabolites are excreted primarily as glucuronide conjugates. Metabolic clearance rates may differ among individuals by several-fold, and this may account in part for the wide variation observed in levonorgestrel concentrations among users.
About 45% of levonorgestrel and its metabolites are excreted in the urine and about 32% are excreted in feces, mostly as glucuronide conjugates.
This product is not intended for use in the premenarcheal population, and pharmacokinetic data are not available for this population.
This product is not intended for use in postmenopausal women, and pharmacokinetic data are not available for this population.
No formal studies have evaluated the effect of race. However, clinical trials demonstrated a higher pregnancy rate in Chinese women with both Plan B and the Yuzpe regimen (another form of emergency contraception). There was a non-statistically significant increased rate of pregnancy among Chinese women in the Plan B One-Step (levonorgestrel tablet) trial. The reason for this apparent increase in the pregnancy rate with emergency contraceptives in Chinese women is unknown [see Use In Specific Populations].
No formal studies were conducted to evaluate the effect of hepatic disease on the disposition of Plan B One-Step (levonorgestrel tablet) .
No formal studies were conducted to evaluate the effect of renal disease on the disposition of Plan B One-Step (levonorgestrel tablet) .
No formal drug-drug interaction studies were conducted with Plan B One-Step [see DRUG INTERACTIONS].
A double-blind, randomized, multicenter, multinational study evaluated and compared the efficacy and safety of three different regimens for emergency contraception. Subjects were enrolled at 15 sites in 10 countries; the racial/ethnic characteristics of the study population overall were 54% Chinese, 34% Caucasian, and 12% Black or Asian (other than Chinese). 2,381 healthy women with a mean age of 27 years, who needed emergency contraception within 72 hours of unprotected intercourse were involved and randomly allocated into one of the two levonorgestrel groups. A single dose of 1.5 mg of levonorgestrel (Plan B One-Step (levonorgestrel tablet) ) was administered to women allocated into group 1. Two doses of 0.75 mg levonorgestrel 12 hours apart (Plan B) were administered to women in group 2. In the Plan B One-Step (levonorgestrel tablet) group, 16 pregnancies occurred in 1,198 women and in the Plan B group, 20 pregnancies occurred in 1,183 women. The number of pregnancies expected in each group was calculated based on the timing of intercourse with regard to each woman's menstrual cycle. Among women receiving Plan B One-Step (levonorgestrel tablet) , 84% of expected pregnancies were prevented and among those women taking Plan B, 79% of expected pregnancies were prevented. The expected pregnancy rate of 8% (with no contraceptive use) was reduced to approximately 1% with Plan B One-Step (levonorgestrel tablet) .
Emergency contraceptives are not as effective as routine contraception since their failure rate, while low based on a single use, would accumulate over time with repeated use [see INDICATIONS AND USAGE].
In the clinical study, bleeding disturbances were the most common adverse event reported after taking the levonorgestrel-containing regimens. More than half of the women had menses within two days of the expected time; however, 31% of women experienced change in their bleeding pattern during the study period; 4.5% of women had menses more than 7 days after the expected time.
Last reviewed on RxList: 7/30/2009
This monograph has been modified to include the generic and brand name in many instances.
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