Hi, Microgynon contains both ethinyl estradiol and levonorgesterol which is used in the prevention of unwanted pregnancies from unprotected sexual activities. It is also used to treat various menstrual problems like heavy, painful or irregular periods. On the other hand, Trimethoprim belongs to the group of medications known as antibiotics is used to treat various bacterial infections like urinary tract infections, respiratory tract infections like certain types of pneumonia etc. Most commonly used antibiotics like Trimethoprim doesn t affect the effectiveness of the birth control pills like Microgynon. So, you can take antibiotics during consuming Microgynon without any tension. But, during taking hormonal birth control pills, you should not take any medications without consulting your doctor first. Take care. Hope I have answered your question. Let me know if I can assist you further. Regards, Dr. Zubayer Alam, General And Family Physician,