Nordette is a combination oral contraceptive that contains both an estrogen (ethinyl estradiol 0.03mg) and a progestin (levonorgestrel 0.15 mg). Miconazole is an over-the-counter antifungal drug used to treat vaginal fungal or yeast infections. Miconazole is available as a vaginal cream or as a vaginal suppository and administered for three to seven days. I am not aware of any reason why miconazole would cause breakthrough bleeding.
However, breakthrough bleeding while on oral contraceptives is common. Over 50% of women may experience breakthrough bleeding during the first three to four months of use of an oral contraceptive. The likelihood of having breakthrough bleeding drops with continued use, but still may be seen in about 10% of women taking oral contraceptives. Although the exact cause is unclear, it may be due to an insufficient amount of estrogen and a thinning of the uterine lining. This thinning may make bleeding more likely just from normal activity.
There are a couple of other factors that can increase the likelihood of breakthrough bleeding. Not taking the pills correctly and smoking can increase the risk of breakthrough bleeding. Another factor is chlamydia infection. Chlamydia is a sexually transmitted disease. Chlamydia infections are very common and are most commonly seen in women under 25 years of age who have had unprotected sex with multiple partners. Although many people with chlamydia have no symptoms, the most common symptoms in women are a burning sensation when urinating, an abnormal vaginal discharge, vaginal bleeding (especially after intercourse) or pain in the pelvis or lower abdomen.
Chlamydia can cause long-lasting problems in women if it is not treated. Antibiotics are used to treat chlamydia infection. Antifungal drugs like miconazole do not work. Because the symptoms are similar, chlamydia infections can be confused with vaginal yeast infection. It is important to make sure the diagnosis is correct. Having drugs like miconazole available without a prescription is convenient because a visit to a health care provider is not needed. This saves time and reduces the cost of vaginal yeast infections in women who have been trained on how to identify the symptoms correctly. Many experts suggest that women not self treat unless they are certain their symptoms are due to a fungal or yeast infection. It is a good idea for women who are experiencing their first vaginal infection to contact their health care professional to make certain the symptoms are caused by yeast and not chlamydia.