For those more medically inclined here are the dosing and Pharmacokinetics information on Levonorgestrel (active ingredient in Plan B one step) direct from Lexi-comp:
DOSING:
When levonorgestrel is used alone as a short-course, progestin-only emergency postcoital contraceptive, a single 1. 5-mg dose of levonorgestrel is administered as soon as possible within 72 hours of unprotected intercourse.Ref132 Alternatively, a levonorgestrel dose of 0.75 mg is administered as soon as possible within 72 hours of unprotected intercourse, followed by a repeat dose of 0.75 mg 12 hours later.Ref101102106126127128 The first dose can be taken up to 120 hours after unprotected intercourse if necessary, but efficacy decreases as initiation of contraception becomes more remote from unprotected intercourse.Ref126127128 A commercial preparation containing 1 levonorgestrel 1. 5-mg tablet (Plan B® One-Step) is available for this purpose.Ref106 A commercial preparation containing 2 levonorgestrel 0. 75-mg tablets (Next Choice®) also is available for this purpose.Ref132 The levonorgestrel postcoital contraceptive regimen may be used at any time during the menstrual cycle.Ref106132 Since postcoital contraceptive efficacy diminishes as the time period between intercourse and administration of the regimen increases,Ref101102103 postcoital contraception with levonorgestrel should begin as soon as possible but within 72–120 hours of unprotected intercourse.Ref101103106 The effectiveness of postcoital contraception administered after more than 120 hours has not been established.Ref126127
The US Food and Drug Administration (FDA) has approved Plan B® One-Step for nonprescription (over-the-counter [OTC]) status for women 17 years of age or older; the contraceptive will remain a prescription-only preparation for women younger than 17 years of age.Ref132 Plan B® One-Step is commercially available in a package that meets the prescription and OTC labeling requirements.Ref132
Absorbtion:
Oral contraceptive steroids are generally well absorbed from the GI tract. Following oral administration, levonorgestrel is completely absorbed. Some oral contraceptive steroids are metabolized in the GI mucosa during absorption and on first pass through the liver. Desogestrel is metabolized in the intestinal mucosa and on first pass through the liver to 3-keto-desogestrel, a metabolite believed to be responsible for the pharmacologic activity of desogestrel.Ref233235 Following oral administration, the absolute bioavailability appears to be about 40% for ethinyl estradiol, 65% for norethindrone, and about 76% for desogestrel or drospirenone. Following oral administration, the relative bioavailability of desogestrel, as measured by serum concentrations of 3-keto-desogestrel (the active metabolite of desogestrel), reportedly is about 84%.Ref235237 Although the absolute bioavailabilities have not been determined, about 60% of norgestimate and 60% of ethynodiol diacetate are reportedly absorbed following oral administration.
Considerable interindividual variation in peak plasma concentrations attained and extent of absorption have been reported for oral contraceptive steroids. Peak plasma concentrations of 100–200 pg/mL are reached 1–2 hours after a 50-mcg dose of ethinyl estradiol; although higher plasma concentrations have been reported, these probably represent methodologic problems. Following single-dose oral administration of ethinyl estradiol 20 mcg (in a fixed combination with levonorgestrel 0.1 mg), mean peak serum concentration was reported to be 50–62 pg/mL at approximately 1.5 hours; at steady state, mean peak ethinyl estradiol concentration of 66–77 pg/mL was reported at approximately 1.3–1.4 hours after administration.
Peak plasma norethindrone concentrations of 1.7–5 ng/mL or 5–10 ng/mL have been reported following a 0.5- or a 1-mg oral dose, respectively. The time to peak plasma norethindrone concentrations varies between 0.5–4 hours, apparently being more delayed as the dose increases.
Following oral administration of a single 0.15-mg dose of desogestrel (given in fixed combination with 30 mcg of ethinyl estradiol), average peak plasma 3-keto-desogestrel concentrations of 2.8 ng/mL are reached within 1.4 hours; at steady state (attained after 19 days or more), average peak plasma 3-keto-desogestrel concentrations of 5.8 ng/mL are reached within 1.4 hours after a dose.Ref235237
Peak plasma norgestimate and 17-deacetyl norgestimate (an active metabolite of norgestimate) concentrations of 0.1 and 3.6 ng/mL are reached within 1 and 1.5 hours, respectively, following oral administration of a single 0.36-mg dose of norgestimate (given in fixed combination with 70 mcg of ethinyl estradiol); at steady state, mean plasma 17-deacetyl norgestimate concentrations of 4.4 ng/mL are reached in about 1.4 hours after a dose.Ref234 Following single-dose oral administration of levonorgestrel 0.1 mg (in a fixed combination with ethinyl estradiol 20 mcg), mean peak serum concentration was reported to be 2.4–2.8 ng/mL at approximately 1.3–1.6 hours; at steady state, mean peak levonorgestrel concentration of 4–6 ng/mL was reported at approximately 1–1.5 hours after administration.
Plasma concentrations of desogestrel, norethindrone, and levonorgestrel at steady state are higher than predicted from single-dose kinetics because of enhanced binding of these progestins following the induction of sex hormone binding globulin (SHBG) by ethinyl estradiol.
Following single-dose oral administration of drospirenone 3 mg (in fixed combination with ethinyl estradiol 30 mcg) in women, mean peak serum concentration was reported to be 36.9 ng/mL at about 1.7 hours; at steady state, mean peak drospirenone concentrations of 78.7–87.5 ng/mL are reached in about 1.6–1.8 hours after a dose.Ref365368 Although steady-state serum concentrations of drospirenone in women with mild renal impairment (creatinine clearance 50–80 mL/minute) generally are similar to those in women with normal renal function (creatinine clearance greater than or equal to 80 mL/minute), drug concentrations in women with moderate renal impairment (creatinine clearance 30–49 mL/minute) are about 37% higher than concentrations in women with normal renal function