Peroralna kontracepcija

Oralno kontracepcija predstavljajo kemične substance, ki jih sprejmemo preko ust in preprečujejo normalno plodnost. Vse delujejo na hormonski sistem. Ženske kontracepcijske tabletke so na tržišču že od zgodnjih 1960-tih in so zelo popularne. Uporablja jih na miljone žensk po celem svetu: približno tretjina spolno aktivnih žensk v Veliki Britaniji, v nekaterih deželah pa dosti manj, recimo na Japonskem. Kontracepcijske tablete za moške so v fazi raziskav in razvoja, tako da še niso na razpolago širokim množicam.

Principi

Kontracepcijske tabletke za ženske so najpogostejša oblika farmakološke kontracepcije. Služijo preprečeanju nosečnosti. Uporabljajo jih tudi za kontrolo disfunkcijskih krvavitev ali na primer za urejanje simptomov policističnih ovarijev. Sestavljene so iz tablet, ki jih ženska jemlje dnevno in vsebujejo doze sintetičnih hormonov (vedno progesterona in pogosto tudi estrogena). Pri določenih tipih tabletk so doze hormonov prilagojene tako, da so v sihronosti z menstrualnim ciklusom (dva do tri fazne tablete), medtem ko imajo druge konstantne koncentracije hormonov.

Mehanizem delovanja

The Pill works by preventing ovulation, as well as making the uterus less likely to accept implantation of an embryo if one is created, and thickens the mucus in the cervix making it more difficult for sperm to reach any egg.

Several different types of 'the Pill' exist. Generally, they all have revolved around different synthetic estrogens and progestins, chemical analogues of the natural hormones estradiol (an estrogen) and progesterone (a progestagen). Most common brands use 20 to 40 micrograms of ethinyl estradiol as the estrogen component and either a fixed or varying (the bi- and triphasic pills) amount of either levonorgestrel or norethindrone as the progestagen component.

Effectiveness

The Pearl Index is often used to compare the effectiveness of various methods of contraception. It is expressed as the "number of pregnancies in 100 normally fertile women over the period of one year". Each method of birth control has two Pearl index numbers:

• method effectiveness: is the Pearl index number for use under perfect conditons. The method effectiveness Pearl index for the Pill has been measured as low as 0.3 and as high as 1.25, which means that under ideal conditions, anywhere from 0.3 to 1.25 out of 100 users will become pregnant during one year of perfect use (Pearl index = 0.3 to 1.25).

• user effectiveness: is the Pearl index number for use under typical conditions. The user effectiveness measured by the Pearl index for the Pill has been measured as low as 2.15 and as high as 8.0, which means that anywhere from 2.15 to 8.0 out of 100 women will become pregnant during the first year of typical use (Pearl index = 2.15 to 8.0).

Many women occasionally forget to take the Pill daily, impairing its effectiveness. Correct use of the pill usually implies taking it every day at the same hour for 21 days, followed by a pause of seven days.

Use of other medications can prevent the Pill from working, due to interactions with the metabolism of the hormonal constituents. Diarrhea will also stop the Pill from working, because the hormones are not properly absorbed by the bowels.

While the Pill is usually effective, its wide availability has not prevented what some call "unwanted pregnancies". In the USA, the rise in widespread use of the Pill has coincided with a rise in the abortion rate to a level that is consistently above 1,000,000 per year, according to AGI statistics. This can be attributed to an increased expectation that sexual intercourse never needs to result in the birth of a baby, even if contraception fails.

Packaging

Half-used blister pack of Levlen®ED

The Pill usually comes in two different packet sizes, and each packet usually has days marked off for a cycle lasting of 28 days. For the 21-pill packet, a woman takes a pill each day for 21 days, and waits for an additional seven days before starting the next packet. For the 28-pill packet, the woman similarly takes a pill each day. However, instead of only taking pills for 21 days of the month, she also takes the remaining seven placebo or sugar pills included in the packet, and once she finishes the last placebo pill, she can immediately start the next packet on the following day. The purpose of the placebo pills is to ensure that the woman, out of habit, can take a pill on every day of her menstrual cycle, so that she does not have to calculate when exactly is the next date that she should start her next packet of pills. It is possible for a woman to skip menstruation and still remain protected against conception by skipping these pills in the cycle. The presence of these pills is still thought to be comforting for the woman as menstruation is a physical confirmation that she is still not pregnant.

Drug interactions

Some drugs reduce the effect of the Pill and can cause breakthrough bleeding, or pregnancy (together with unprotected sex, of course). These include antibiotics, barbiturates, phenytoin and carbamazepine. The traditional medicinal drug St John's Wort has also been implicated.

Stranski učinki

Določene ženske se po tem, ko začnejo jemati kontracepcijske tablete, rahlo zredijo. Ta stranski učinek je individualne narave, saj se določene ženske ne zredijo, nekatere pa, ki že imajo zvišano telesno težo, pa se še dodatno zredijo. Določene ženske opazijo tudi spremembe v intenzivnosti želje po spolnosti, spremembe vaginalnega izcedka in menstruacije.

Drugi stranski učinki so še: slabost, glavoboli, depresija, vaginitis, urinarni infekt, spremembe dojk, spremembe na koži in vnetje dlesni.

Cautions and contraindications

Oral contraceptives may influence coagulation, increasing the risk of blood clots causing deep venous thrombosis (DVT) and pulmonary embolism, stroke and myocardial infarction (heart attack). This is especially so in women who already have some pre-existing cardiovascular disease, in women who have a familial tendency to form blood clots (such as familial factor V Leiden), women with obesity or hypercholesterolaemia (high cholesterol level) and in smokers.

The Pill has also been linked to an increased risk of breast cancer, although newer Pill types may not influence breast cancer risk. In rare cases, high estrogen Pills may trigger benign intracranial hypertension. Women who use the Pill have an increased chance of developing certain serious problems that can be fatal. Benign liver tumors have been reported.

The chance of developing most of the above problems increases with age - especially when certain other health problems are present. The risks are even greater for women who are age 35 or older, smoke more than 15 cigarettes a day, or have conditions associated with heart attack, such as diabetes, high blood pressure, or high levels of cholesterol, and certain inherited conditions that increase the risk of blood clotting. Women using the Pill who undergo major surgery seem to have a greater chance of having blood clots.

Benefits

Aside from being a contraceptive and for management of irregular periods, there may be incidental benefits to the Pill. There is some evidence that use of the pill might reduce the incidence of ovarian cancer and endometrial cancer . Given that the benefits are less well researched or highlighted than the risks, the question arises as to how the reduction in incidence of these cancers compares against the increased risks of developing breast cancer or deep-vein thrombosis.

History

The invention

Carl Djerassi (1923-) invented norethindrone in the 1950s. The Pill was developed in the 1950s by Gregory Pincus with the encouragement and financial backing of birth control activists Margaret Sanger and Katharine McCormick.

The FDA approved it for clinical use on May 9, 1960. It took various high-profile court cases, such as Poe v. Ullman and Griswold v. Connecticut, to make it available to all women of reproductive age.

France

The Pill was rendered legal in 1967 after the introduction of the Neuwirth Law.

Japan

In Japan, continual debates over safety and sexually-transmitted infection risks (raised over concerns that oral contraceptive use will diminish condom use) have led to the Pill being banned for nearly 40 years, and its recent introduction has seen very few women take it up.

References

1. ^ Pearl R. Factors in human fertility and their statistical evaluation. Lancet 1933;2:607-611.
2. ^ Data based on article: Audet MC, Moreau M, Koltun WD, Waldbaum AS, Shangold G, Fisher AC, Creasy GW. Evaluation of contraceptive efficacy and cycle control of a transdermal contraceptive patch vs an oral contraceptive: a randomized controlled trial. JAMA. 2001;285(18):2347-2354. (http://www.contraceptiononline.org/slides/slide01.cfm?q=pearl+index&dpg=6)
3. ^ Alan Guttmacher Institute, Facts in Brief, First Year Contraceptive Failure Rates (http://www.agi-usa.org/pubs/fb_contr_use.html). Retrieved May 10, 2005.
4. ^ Reduction in ovarian & endometrial cancer study. http://content.nejm.org/cgi/content/abstract/316/11/650
5. ^ Hormonal contraceptive use in Japan, 2004 news article. (http://www.cbsnews.com/stories/2004/08/20/health/main637523.shtml)

See also

• Morning-after pill