What is Plan B and Fluconazole?
Plan B, also known as Plan B One-Step, is an over-the-counter emergency contraception pill. Its active ingredient is a high dose of the synthetic hormone levonorgestrel, which works by preventing ovulation or fertilization. It is designed to be taken within 72 hours of unprotected intercourse, though it is most effective the sooner it is taken.
Fluconazole (brand name Diflucan) is a prescription antifungal medication used to treat fungal infections, most commonly yeast infections (candidiasis). It works by disrupting the fungal cell membrane, ultimately killing the yeast. Fluconazole is taken orally as a tablet or capsule.
The Pharmacological Interaction Between Plan B and Fluconazole
When you take Plan B and Fluconazole together, a moderate drug interaction occurs. This interaction is related to how your body's enzymes process each medication. The main mechanism is as follows:
- Fluconazole is a potent inhibitor of certain liver enzymes, particularly the cytochrome P450 enzyme CYP3A4.
- Levonorgestrel, the active component of Plan B, is also metabolized by these same liver enzymes.
- By inhibiting the enzymes, fluconazole slows down the rate at which your body can clear the levonorgestrel from your system.
- This slower metabolism leads to an increase in the concentration of levonorgestrel in your bloodstream.
It is important to note that studies evaluating fluconazole's effect on oral contraceptives containing levonorgestrel found that while hormone levels did increase, it did not lead to a threat of contraceptive failure. However, the increased hormone levels can lead to a higher incidence or severity of side effects.
Potential Side Effects of Combining the Medications
While the primary concern for many is the effectiveness of Plan B, the most likely consequence of this interaction is an increase in side effects. Both medications carry their own potential adverse effects, and combining them can exacerbate those symptoms. The increased levonorgestrel levels in your system can heighten hormonal side effects.
- Nausea and Vomiting: Both Plan B and fluconazole list nausea and vomiting as potential side effects. Taking them together can increase the risk or severity of these gastrointestinal issues. If you vomit within 2-3 hours of taking Plan B, you should talk to a healthcare professional, as you may need to repeat the dose.
- Vaginal Bleeding: Some women report irregular or breakthrough bleeding when taking fluconazole and hormonal contraceptives. The higher levonorgestrel concentration can also cause changes in your bleeding pattern.
- Headache and Dizziness: Both medications can cause headaches and dizziness independently. Taking them concurrently may lead to a higher frequency or intensity of these symptoms.
- Breast Tenderness: Breast tenderness is a very common side effect of Plan B due to the high dose of hormones. Fluconazole can also cause breast tenderness, and combining them could increase this symptom.
Comparison Table: Side Effects of Plan B vs. Fluconazole
| Side Effect | Plan B One-Step (Levonorgestrel) | Fluconazole (Diflucan) | Combined Risk Profile |
|---|---|---|---|
| Nausea | Very common (up to 23.1%) | Common | Increased frequency and severity |
| Abdominal Pain | Very common (up to 22.6%) | Common | Increased discomfort |
| Headache | Very common (up to 16.8%) | Common | Increased frequency and severity |
| Dizziness | Common (11.2%) | Common | Potential for heightened symptoms |
| Vaginal Bleeding | Very common (changes in menstrual pattern) | Possible (breakthrough bleeding) | Possible increase in irregular bleeding |
| Breast Tenderness | Common (10.7%) | Possible | Potential for heightened tenderness |
Practical Advice for Taking Both Medications
If you find yourself needing to take Plan B for emergency contraception and fluconazole for a yeast infection, here are some key steps to follow:
- Prioritize Plan B: The time-sensitivity of emergency contraception is critical for its effectiveness. Take Plan B as soon as possible after unprotected sex.
- Consult a Professional: Call your doctor or a pharmacist to discuss your specific situation. While the interaction is generally not considered to compromise contraceptive efficacy, professional guidance can help manage potential side effects and ensure your situation is appropriate for the combination.
- Consider Timing (if feasible): One source suggests waiting at least 3-5 days before taking fluconazole after Plan B if there is no urgency, but others state it can be taken without delay. This highlights the need for professional advice based on your medical history.
- Manage Side Effects: Be prepared for potentially increased nausea or discomfort. Consider taking Plan B with food to help reduce nausea. If vomiting occurs within 2-3 hours of taking Plan B, contact a healthcare provider.
- Use Backup Contraception: Plan B is not as reliable as regular contraception. After taking it, use a barrier method like a condom until your next period to prevent pregnancy.
Conclusion
While a moderate drug interaction exists between Plan B (levonorgestrel) and fluconazole, the combination is generally considered safe and is not expected to reduce the effectiveness of your emergency contraception. The interaction can, however, increase the concentration of levonorgestrel in your system, which may heighten typical hormonal side effects such as nausea, dizziness, and irregular bleeding. To ensure the safest and most effective outcome, prioritize taking Plan B as soon as possible and consult with a healthcare provider regarding the timing and management of fluconazole treatment. Openly discussing all medications and potential side effects with a professional is the best course of action.
Further Reading
- American College of Obstetricians and Gynecologists (ACOG): Emergency Contraception
