Conception control by a single monthly injection

Vaginal bleeding patterns in women using once-a-month injectable contraceptives

The main raison d'être for the development of once-a-month injectable contraceptives is the need for a long-acting method which produces a regular vaginal bleeding pattern. Although many women will successfully tolerate the amenorrhea or irregular bleeding which frequently accompany use of long-acting progestogen-only methods, there is a substantial minority, especially in certain ethnic groups, who find this unacceptable. The extensive literature does indicate that although combined estrogen-progestogen once-a-month injectables produce much more regular bleeding patterns than long-acting injectables like depot-medroxyprogesterone acetate, the patterns are not entirely normal. Detailed studies by the World Health Organization have demonstrated some deviation from normal menstrual patterns by users of the two once-a-month injectables, Cyclofem and Mesigyna. For example, 23.5% of Cyclofem and 25.2% of Mesigyna users experience irregular bleeding between 3 and 6 months of use compared with 4.8% of untreated women, and 13.3% of Cyclofem and 11.1% of Mesigyna users experience prolonged bleeding compared with 2.3% of untreated women. Comparable figures are much worse for DMPA users with a 35.7% incidence of irregular and 27.7% incidence of prolonged bleeding after similar duration of use. Bleeding patterns with all long-acting methods tend to improve with time. Overall group data for once-a-month injectable users are reasonably close to those of untreated women with, for example, a median of 15.6 days (5th and 95th percentiles: 7.5 and 26; confidence limits) of bleeding or spotting per 90-day reference period compared with a median of 18.5 days (5th and 95th percentiles: 12.2 and 25.5) for untreated women. Twelve-month life table discontinuation rates for menstrual bleeding disturbances are lower than expected for most progestogen-only methods at 2.1-5.2% for Cyclofem and 0.8-4.2% for Mesigyna for amenorrhea, and 6.3-12.7% for Cyclofem and 7.5-12.0% for Mesigyna for bleeding-related reasons. Once-a-month injectable contraceptives produce vaginal bleeding patterns much closer to normal than other injectables, but there are still significant deviations which lead to some discontinuation for menstrual reasons. Hence, full explanation and counselling about possible menstrual changes are still essential for all intending users of these methods.

Once-a-month injectable contraceptives: efficacy and reasons for discontinuation

Reports of the phase III clinical trials on four combined progestogen-estrogen once-a-month injectable contraceptives, Deladroxate, Cyclofem, Mesigyna and Chinese Injectable No. 1, are reviewed focussing on efficacy and reasons for discontinuation. Deladroxate, currently used in many Latin American countries has proved to be highly effective and well accepted. However, this combination was withdrawn by the original manufacturer because the progestogen component of this drug induced a high number of breast cancers in dogs and very curious pituitary hyperplasia in rats. Cyclofem and Mesigyna were found to be highly effective and highly acceptable drugs. Side-effects were minimal and were of minor importance. The Chinese Injectable No. 1 had unacceptably high failure rates with a monthly injection schedule. After doubling the dose in the first month of use, the efficacy was satisfactory. It was found that all monthly injectable contraceptives provided better cycle control than the every 3 months depot-medroxyprogesterone acetate, although abnormal bleeding was still the main drug-related complaint and reason for discontinuation. Missed appointment is another reason for discontinuation which might reflect the problem of frequent injection schedule, thus indicating the need for proper selection of the users and good counselling.

Long acting contraceptives. Present status

Long acting injectable hormonal contraceptives are among the most effective fertility regulating agents developed; yet they are also among the most controversial because of animal data indicating a possible carcinogenic potential in several species. A critical analysis of these animal findings has revealed, in all instances, the existence of specific mechanisms not occurring in the human. For this reason, most national and international scientific bodies who have reviewed this issue have concluded that there are no toxicological reasons for not using long acting hormonal contraceptives. Long acting agents can be divided into 2 separate groups: those having a duration of action of one month, which are composed of a long acting oestrogen and a progestagen, and those lasting for several months which consist of only a progestagen. Among the injectable progestagen-only contraceptives tested, only 2 have so far reached the international market: depot medroxyprogesterone acetate (DMPA), which has been administered at 3- or 6-month intervals and norethisterone enanthate, which has been injected at intervals ranging between 2 and 3 months. The most important side effect observed with these 2 agents is a complete disruption of the menstrual bleeding pattern, leading - in some cases - to total amenorrhoea, which is more frequent with depot medroxyprogesterone acetate than with norethisterone enanthate. The latter, however, has a shorter duration of action with a higher pregnancy rate than the former. Other adverse reactions are rare and of no real importance. Metabolic effects with progestagen-only injectable preparations are, in general, mild and less marked than with combined oestrogen-progestagen formulations. Recent investigations have shown that the return of fertility following their use is delayed but in no way impaired. Monthly injectable oestrogen-progestagen combinations have been tested to a more limited extent and these agents are available only in a very few countries. Their main advantage over progestagen-only preparations is that they allow a reasonable menstrual bleeding pattern in the majority of cases. Their obvious disadvantage is that they contain a long acting oestrogen.