(Table 61.2). Because of an increased incidence of certain side effects and slightly decreased contraceptive activity, progestin-only oral contraceptives are not extensively used. The undesirable side effects associated with progestin-only contraceptives are irregular bleeding episodes, headache, weight gain, and mood changes. Progestin-only contraceptive devices are used. The Norplant System for contraception consists of a series of levonorgestrel-filled pliable plastic tubes that are implanted subcutaneously on the inside of the upper arm by a physician. While one set of six tubes can remain effective for up to 5 years, the contraceptive effects are readily reversible with removal of the implant. Adverse effects are similar to those seen with other progestin-only contraceptives; however, accidental pregnancy is less frequent.

Mirena is a relatively new intrauterine contraceptive device that releases levonorgestrel into the uterine cavity for 5 years. Use of this contraceptive device is associated with fewer systemic progestin side effects and is at least as effective as Norplant.

Abortifacients and Emergency Contraceptives

Progesterone is a hormone required for the maintenance of pregnancy. Termination of early pregnancy is effected using the steroidal antiprogestin drug, mifepri-stone (RU486), which acts by blocking progestin binding to the progesterone receptor. A single oral dose of RU486 followed by a single dose of a prostaglandin (Misoprostol) 48 hours later is 90 to 95% effective in terminating pregnancy. The side effects are generally mild except for heavy bleeding. Severe cardiovascular complications have occurred and may be due to the prostaglandin component of this treatment. The use of RU486 is therefore contraindicated in women at risk for cardiovascular disease, including smokers and women over 35 years of age.

High-dose estrogen and high-dose progestin are effective in emergency contraception when given immediately following unprotected coitus. Plan B is an emergency contraceptive kit consisting of two tablets of the progestin levonorgestrel (0.75 mg).The first tablet must be taken as soon as possible but no later than 3 days after coitus, and the second tablet is taken 72 hours later. This regimen is more effective and better tolerated than the Preven emergency contraceptive kit, an estrogen-progestin combination (two tablets of 50 ^g ethinyl estradiol and two tablets of 0.25 mg of levonorgestrel). The high doses of estrogen in the Preven regimen are associated with severe nausea and vomiting.

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