Till Örebro universitet

Objective: To investigate if continuation rates in first-time users of oral hormonal contraceptives differed between different formulations and to measure if the rates were related to the prescribing categories, that is, physicians and midwives.

Design: A longitudinal national population-based registry study.

Setting: The Swedish prescribed drug register.

Participants: All women born between 1977 and 1994 defined as first-time users of hormonal contraceptives from 2007 to 2009 (n=226211).

Main outcome measures: A tendency to switch the type of hormonal contraceptive within 6months use and repeated dispensation identical to the first were estimated as percentages and relative risks (RRs). Physicians' and midwives' prescription patterns concerning the women's continuation rates of oral hormonal contraceptive type.

Results: In Sweden, there were 782375 women born between 1977 and 1994 at the time of the study. Of these, 226211 women were identified as first-time users of hormonal contraceptives. Ethinylestradiol+levonorgestrel, desogestrel-only and ethinylestradiol+drospirenone were the hormonal contraceptives most commonly dispensed to first-time users at rates of 43.3%, 24.4% and 11.1%, respectively. The overall rate of switching contraceptive types in the first 6months was 11.3%, which was highest for desogestrel-only (14.3%) and lowest for ethinylestradiol+drospirenone (6.6%). The switching rate for all three products was highest in the 16-year to 19-year age group. Having a repeated dispensation identical to the initial dispensation was highest for users of ethinylestradiol either combined with levonorgestrel or drospirenone, 81.4% and 81.2%, respectively, whereas this rate for the initial desogestrel-only users was 71.5%. The RR of switching of contraceptive type within the first 6months was 1.35 (95% CI 1.32 to 1.39) for desogestrel-only and 0.63 (0.59 to 0.66) for ethinylestradiol+drospirenone compared with ethinylestradiol+levonorgestrel as the reference category. There were no differences in the women's continuation rates depending on the prescriber categories.

Conclusions: Desogestrel-only users conferred the highest switcher rate to another hormonal contraceptive within a 6-month period. Users of ethinylestradiol+levonorgestrel were more prone to switch to another product within 6months than women using ethinylestradiol+drospirenone. These findings may be of clinical importance when tailoring hormonal contraceptives on an individual basis.