Chapter: Basic & Clinical Pharmacology : The Gonadal Hormones & Inhibitors
Hormonal Contraception
HORMONAL CONTRACEPTION (ORAL,
PARENTERAL, & IMPLANTED CONTRACEPTIVES)
A large number of oral
contraceptives containing estrogens or progestins (or both) are now available
for clinical use (Table 40–3). These preparations vary chemically and pharmacologically
and have many properties in common as well as definite differences important
for the correct selection of the optimum agent.
Two types of
preparations are used for oral contraception:
combinations of estrogens and progestins and
(2) continuous progestin therapy without concomitant administration of
estro-gens. The combination agents are further divided into monophasic forms (constant dosage of
both components during the cycle) and biphasic
or triphasic forms (dosage of
one or both components ischanged once or twice during the cycle). The
preparations for oral use are all adequately absorbed, and in combination
prepara-tions the pharmacokinetics of neither drug is significantly altered by
the other.
Only one implantable
contraceptive preparation is available at present in the USA. Etonogestrel,
also used in some oral contra-ceptives, is available in the subcutaneous
implant form listed in Table 40–3. Several hormonal contraceptives are
available as vaginal rings or intrauterine devices. Intramuscular injection of
large doses of medroxyprogesterone also provides contraception of long
duration.
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