The injectable contraceptive : user, social and pharmacological perspectives.
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Date
2003
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Abstract
Despite its widespread use, little research has been undertaken on the use of progestogen-only injectable contraceptives by South African women. This thesis is comprised of two sections. Section 1 provides the first comprehensive description of injectable contraceptive use among rural South African women. It includes an analysis of the contraceptive method mix, prevalence of injectable contraceptive use, discontinuation patterns and reported side effects. A comparison of depot medroxyprogesterone acetate (DMPA) versus norethisterone oenanthate (NET-EN) focuses on utilization patterns and costs. The second section gives an account of the pharmacokinetics of DMPA including the first ever population analysis. A cross-sectional, community-based household survey was undertaken in the Hlabisa sub-district of KwaZulu-Natal, South Africa. Interviews were held during 1998 and 1999, with 848 randomly selected women (aged 15-49 years) and with 14 focus groups. There was a heavy reliance on injectable contraceptives which were used by 74% of women practising contraception. By contrast, the condom was the current method of only 4%. The injectable method was the most commonly used method among teenagers. However, in most cases, contraceptive use appeared to commence only after the first pregnancy. Slightly more NET-EN (54%) than DMPA (46%) was used, with younger women more likely to use NET-EN than DMPA (p=0.001). No significant differences in self-reported side effects were found between current users of the two injectables. Health workers played an important role in women's decisions to use the injectable, and in product selection, with NET-EN being recommended for younger women on the basis of concerns about method reversibility. While some women used injectables for long periods of time, discontinuation rates at two years were high, most commonly due to menstrual
disturbances. Many side effects were reported by users of both DMPA and NET-EN, with amenorrhoea the most common, experienced by 63% of current injectable users. Heavy bleeding was most commonly reported by previous users (38%). Vaginal wetness was also common, mentioned by 18% and 29% of current and previous users respectively. Utilisation patterns of the two injectable products (DMPA and NET-EN) were analysed by means of a Pareto analysis of injectables issued from four South African provincial pharmaceutical depots over three financial years (1997/8, 1998/9 and 1999/2000). Injectables accounted for a substantial share of total state expenditure on drugs. While
more DMPA than NET-EN was issued, NET-EN distribution from two depots increased over the period of analysis, even though DMPA was the cheaper option. The pharmacokinetic analysis was undertaken amongst DMPA users routinely attending family planning services in three Durban clinics in 1996. Medroxyprogesterone acetate levels at the end of the dosing interval were analysed for 94 women. In addition a
population pharmacokinetic analysis of 291 serum levels from 111 DMPA users was undertaken. This involved the use of Non Linear Mixed Effect Modelling (NONMEM) to fit the data and determine the pharmacokinetic parameters, apparent clearance (CLIP) and apparent volume of distribution (VIP), and to estimate the influence of covariates on CLIP and VIP (where P is the bioavailability). The final model estimates for CLIP and VIP were 1080 (95% confidence interval: 994, 1166) litres/day and 86200 litres (95% confidence interval: 68246, 104154) respectively. No significant relationships were found between the covariates tested and CLIP and VIP. Concerns raised in the literature about
the influence of weight or ethnicity on the pharmacokinetics of DMPA were shown to be unfounded. In the context of South Africa's HIV epidemic, the heavy reliance on injectable contraceptives, which offer no protection against HIV, should be addressed by expanding the contraceptive method mix to include barrier methods such as the female condom. Health providers are influential in contraceptive decision-making and should be encouraged and supported to redress the dependence on the injectable method alone, taking into account the need of many for dual protection against HIV and unwanted pregnancy. Provider counseling should also focus on adherence to dosing regimens,
improving continuation rates, and should provide appropriate advice for women complaining about vaginal wetness with injectable use. Promotion of one injectable product over another to younger women is not appropriate. Since DMPA is the cheaper product, provider training about the rational use of injectable contraceptives should include cost considerations.
Description
Thesis (Ph.D.)-University of Natal, 2003.
Keywords
Contraceptives., Pharmacokinetics., Contraceptive drugs, Injectable., Theses--Clinical pharmacology.