Introduction

Article Abstract:

The functions of oral contraceptives are to reliably prevent ovulation, control the menstrual cycle, and cause a minimum of side effects. Oral contraceptives have been approved because their effects and side effects are acceptable in the general population. However, this means that even low-dose contraceptives are an overdose for most women, since they must be able to suppress ovulation in all women. However, responses, side effects, and susceptibilities to oral contraceptives vary in the individual. Attempts to obtain optimum conditions in individuals are difficult, as the pharmacokinetics - tissue handling properties - of these very powerful drugs vary among individuals and even within individuals over time. Fortunately, the margin between therapeutic effect and toxic effects is wide, and adverse effects such as liver damage, stroke, and clot formation are rare. However, it is important to understand the factors that influence the pharmacokinetics of the oral contraceptives so as to obtain the best dosage with minimum side effects. Past understanding of the effects of progesterone and estrogen, the two hormonal components of oral contraceptives, has been limited and has sometimes erred greatly. Most practicing physicians concerned with contraceptive use are more concerned with dosage than with pharmacokinetics. The symposium to which this article is an introduction is intended to increase attention toward an understanding of this topic. (Consumer Summary produced by Reliance Medical Information, Inc.)

History, editorial

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Conclusion

Article Abstract:

The findings presented during a symposium on tissue handling of oral contraceptives and drug and disease interactions are summarized. Both scientists and practitioners participated in the symposium, with the idea of improving understanding and usage of oral contraceptives as well as elaborating new questions about contraceptive effects. Variability between and within individuals in the achievement of steady blood levels of steroids, particularly with different relative dosages of estrogens and progesterones, was an important subject raised. These steroids have important effects on liver metabolism and on levels of proteins available to transport the steroids in blood. Differences in gastrointestinal metabolism of estrogens also play a role in determining the blood levels. Cellular responses to the steroids depend on the blood levels, levels of transport protein, and extent of receptors (steroid-selective proteins) within the cells. The liver pathways for metabolism of estrogen and probable effects of progesterones on these reactions are reviewed. Potential effects of antibiotics on contraceptive effectiveness are discussed, as are aspects of contraceptive use in patients with certain conditions such as cardiovascular disease or altered gastrointestinal function. Many questions about contraceptive steroid handling by tissues remain unanswered and must await further research. (Consumer Summary produced by Reliance Medical Information, Inc.)

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Pharmacokinetics and pharmacodynamics of oral contraceptive steroids: factors influencing steroid metabolism

Article Abstract:

The relationship between dosage of oral contraceptives and actual blood levels of the steroids used in these formulations is not straightforward due to wide individual variability and to effects of progesterone and estrogen on each other's metabolism and transport in blood. It is important to improve understanding of tissue handling of these drugs and how the pharmacokinetics is altered, so that doses, and possible side effects, can be kept as low as possible. Much information is available on single-dose effects, but contraceptives are generally used for long periods of time, and more extended studies are more appropriate. The changes in blood levels of steroids in 22 women taking contraceptives with estrogen and various progesterones were evaluated over 12 months. Progesterone levels increased up to day 21 of each cycle, with a maximum achieved between the third and sixth cycles. Estrogen levels increased up to day 10. Progesterones affected estrogen levels, and different progesterones differed in the extent of these effects. Large variations between individuals and within an individual over time were found. The rise in blood levels of steroids was attributed to inhibition of steroid metabolism in the liver. Much research is needed before most aspects of contraceptive steroid handling are understood. (Consumer Summary produced by Reliance Medical Information, Inc.)

Research, Steroid hormones

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