Co-trimoxazole modestly increases ethinylestradiol levels. However, there are about 15 anecdotal cases on record of contraceptive failure attributed to
co-trimoxazole. There are also isolated cases of contraceptive failure attributed to various sulphonamides, and
trimethoprim.
Not established. The pharmacokinetic and pharmacodynamic evidence indicates that
co-trimoxazole is not likely to reduce the effectiveness of combined hormonal
contraceptives. Although there are a number of reports of contraceptive failure attributed to
co-trimoxazole, these are anecdotal and unconfirmed. It is possible that these cases are coincidental, and fit within the normal failure rate of combined hormonal
contraceptives. It has been said that it is almost certain that
co-trimoxazole does not interact with combined hormonal
contraceptives.