Page 70 - 《中国药房》网络版 2018年6月第2期科普版

《中国药房》网络版 2018 年 6 月第 2 期科普版 Jun No.2 2018 China Pharmacy online Popular Science Edition

of oral contraceptives and St John’s wort has been published, and it
3
provides new insights into this drug interaction. The study involved a

search of PubMed and the Cochrane database, in which it identified 48
articles dealing with the interaction of St John’s wort with oral

contraceptives. Of these, just 4 studies compared the use of oral

contraceptives alone with the combined use of St John’s wort and oral

contraceptives and met their rigorous inclusion criteria. The results

suggest that the interaction is real and that pharmacist intervention is

warranted.

In one study of 12 women using oral contraceptives (ethinyl estradiol 35

mcg, norethindrone 1 mg), the subjects took the oral contraceptive alone

for 1 month and then added St John’s wort 300 mg 3 times a day (hypericin

4
content 0.3%) for the next 2 months. During month 1, just 2 of the 12
women had breakthrough bleeding, but by the third month, more than half

(7 of 12) did. Also, in the presence of St John’s wort, ethinyl estradiol
half-life was reduced to about half of its control values.

Another study of 16 women on ethinyl estradiol 20 mcg and norethindrone

1 mg compared 2 cycles with the oral contraceptive alone to 2 cycles with

5
added St John’s wort 300 mg 3 times a day (hypericin content 0.3%). With
the addition of St John’s wort, breakthrough bleeding rose from 19% to

50%, accompanied by modest reductions in ethinyl estradiol and

norethindrone area under the curve. Also, during St John’s wort

administration, more women had follicles over 30 mm and more had probable

ovulation.

Using a randomized crossover design, in a third study, 17 women taking

ethinyl estradiol 20 mcg plus desogestrel 0.15 mg were studied for 1 month

66