Hormonal Steroid Contraceptives II: Clinical Considerations

Summary

Measured in terms of the problems of world population control, hormonal contraceptives have contributed little; a mere 17 million women using them at the present time. However, in certain Western countries, notably Australia, New Zealand and the United States of America, the impact of oral contraception has been considerable. In developing countries experience with hormonal steroids has been disappointing, mainly because motivation is poor and because supervision by medical or para-medical personnel is lacking. Thus, viewed in its relation to the world scene, hormonal contraception can be regarded as adding to the comfort and happiness of the people of nations who are already relatively comfortable and happy.

In our society, the acceptance of oral contraception that has led to it becoming the most commonly used form of contraception depends on several factors. Foremost is effectiveness. The combined oestrogen-progestagen preparations are virtually 100 % effective when used correctly and sequential regimens are only marginally less so. There has been ready acceptance by the medical profession who have found the prescription of pharmacological agents to be more in keeping with their traditional approach to medicine than the dispensing of mechanical and other contraceptives for which they have often been poorly trained.

Many minor side-effects attributed to hormonal steroids are subjective in nature and susceptible to both user and observer bias. There is a paucity of adequately controlled studies from which conclusions can be drawn about the incidence of such symptoms, particularly those of a psychological kind. Nevertheless, certain side-effects such as nausea and oedema can be related to oestrogen, and others, such as reduced menstrual flow and migrainous headaches, can be related to progestagen.

The evidence suggesting an association of oestrogen administration with thrombo-embolism has led to the recommendation that oral contraceptives containing 50 μg of either ethinyloestradiol or mestranol should be used in preference to those containing higher doses. The 50 μg dose of oestrogen has been combined by most manufacturers with a dose of a progestagen which is the lowest compatible with effectiveness and satisfactory cycle control. Consequently, of the many preparations available, there are 6 different formulations from which an initial choice will be made in most instances. There is no evidence that any one of these is more effective or has fewer side-effects than the others.

Increasing use is being made of preparations containing progestagen alone. Chlormadinone acetate 0.5 mg has been available as a tablet for continuous administration. It is less effective than combined or sequential preparations and erratic bleeding is a common side-effect. However, other minor side-effects are virtually absent and there are no absolute contra-indications. The injectable depot progestagen, medroxyprogesterone acetate (150 mg), is given at intervals of 3 months. Effectiveness is comparable to that of combined oral regimens, although erratic bleeding is frequent in the early months of use and amenorrhoea is usual after 9 to 12 months.

There are several new regimens under clinical trial at present which show promise of being useful additions to the present range. These include reverse sequential regimens and sustained-release low dose progestagens. It is apparent that although combined oral contraceptives containing 50 μg of oestrogen will hold pride of place for some time to come, there is a move towards regimens that contain no oestrogen or in which the duration of administration of oestrogen, and its total dosage, is substantially reduced. Intense interest centres on the possibilities of self-administered prostaglandins to interrupt pregnancy within a few days of the first missed period.