Hormonal contraception: present and future

Abstract

The original form of hormonal contraception ("the Pill") has developed into a variety of modalities administered through different routes: oral, intramuscular, subcutaneous, transdermal, intrauterine or intravaginal, and intranasal (abandoned). At present, two separate methods of hormonal contraception exist; one is used to prevent fertilization and the other to prevent pregnancy. From a pharmacological point of view, hormonal methods utilize either a combination of estrogen and progestin or progestin alone. Today all combined methods contain ethynylestradiol, and over the years there has been a substantial reduction in its dosage from almost 80 microg to as low as 15 microg. On the other hand, a variety of progestins are currently utilized that belong to two main chemical families: derivatives of progesterone and derivatives of 19-nortestosterone or gonane. These compounds, developed over a period of 50 years, can be distinguished in four successive "generations". Recent developments include new oral regimens intended to change the 7-day medication-free interval and new commercial preparations; the latter utilize the progestins drospirenone and dienogest. In addition, an oral contraceptive containing chlormadinone has also been marketed. Besides the oral route, contraceptive systems exist or are under development that employ the intramuscular, transdermal and intravaginal routes; they deliver both an estrogen and a progestin. Several patches and vaginal rings are also marketed. A variety of long-acting methods delivering only a progestin are also available. They use the subcutaneous route or are released from an intrauterine system, both of which provide optimal contraceptive protection and, depending on the system, can last up to 5 years (and probably more). Finally, progestin-releasing vaginal rings are under investigation. The second type of hormonal contraception, called "emergency contraception", utilizes progestins and antiprogestins and to be effective should be taken as soon as possible after unprotected intercourse.