Thank you for your question. Sulfasalazine (Salazopyrin EC 500) is an antibiotics which can reduce the efficacy of oral contraceptive medication containing ethinylestradiol and norgestimate such as Cilest. As a result, you can be at increased risk for pregnancy or developing breakthrough uterine bleeding. We strongly recommend that you use barrier protection such as condoms while you are on this medication to prevent unwanted pregnancy. It is important to note that after you complete your course of antibiotics, that your birth control medication may still be ineffective, so it is important that you continue to use additional protection to prevent pregnancy until you have your regular menstrual period.
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