Understanding Nystatin and How It Works
Nystatin is a polyene antifungal medication used to treat Candida yeast infections [1.4.4]. It's most commonly prescribed for infections like oral thrush (oropharyngeal candidiasis) and candidiasis of the skin or gastrointestinal tract [1.4.1].
Its mechanism of action is highly specific. Nystatin works by binding to a substance called ergosterol, which is a vital component of the fungal cell membrane. Human cells have cholesterol instead of ergosterol, making them less susceptible to the drug's effects [1.4.3]. This binding action creates pores in the fungal cell membrane, causing the cell's contents to leak out, which ultimately kills the fungus [1.4.6, 1.4.7]. This targeted action is a primary reason for its effectiveness and safety profile.
The Critical Factor: Poor Absorption Means Few Interactions
The most important concept to understand about nystatin, particularly when taken orally (as a liquid or tablet), is that it has poor absorption from the gastrointestinal (GI) tract [1.4.2]. This means very little of the drug enters the bloodstream. Instead, it acts locally on the surface of the mouth and gut to eliminate the fungal infection [1.4.1].
Because nystatin isn't circulating systemically throughout the body in significant amounts, it cannot interfere with the metabolism or function of other drugs that are in the bloodstream. This is the fundamental reason why multiple major health sources, including the NHS and RxList, state that nystatin has no known serious or moderate drug interactions [1.2.1, 1.2.3]. It is excreted from the body almost entirely unchanged in the feces [1.4.2].
Known and Potential Nystatin Interactions
While interactions are rare, a few specific substances are known to be affected by nystatin.
1. Saccharomyces boulardii (Yeast-Based Probiotics)
The most well-documented interaction is with Saccharomyces boulardii, a beneficial yeast often sold as a probiotic (e.g., Florastor) [1.3.1, 1.5.4]. Since nystatin is an antifungal designed to kill yeast, taking it at the same time as a yeast-based probiotic will render the probiotic ineffective [1.5.2]. The nystatin will simply kill the beneficial yeast you are trying to supplement with. For this reason, it is advised to avoid using these specific probiotics while on nystatin therapy [1.4.2]. Probiotics that are bacteria-based are not affected.
2. Progesterone
Some drug databases note a potential interaction where nystatin might decrease the absorption of progesterone [1.6.1]. However, evidence for this is limited, and it is not universally listed as a significant clinical concern. The NHS states that nystatin does not affect any type of hormonal contraception [1.6.2]. Patients taking progesterone should still mention their nystatin use to their doctor as a precaution.
3. Allogeneic Cultured Keratinocytes/Fibroblasts
This is a specific type of skin graft material (a bioengineered living cell therapy). Nystatin is listed as contraindicated because topical antibiotics can degrade the product [1.3.1, 1.3.6]. This is a highly specialized interaction relevant only in specific wound care settings.
Comparison Table: Nystatin vs. Systemic Antifungals
To highlight nystatin's unique safety profile, it's helpful to compare it to a systemic antifungal like fluconazole.
| Feature | Nystatin | Fluconazole |
|---|---|---|
| Mechanism | Binds to ergosterol, creating pores in the fungal cell membrane [1.4.2]. | Inhibits an enzyme needed to produce ergosterol, disrupting membrane formation. |
| Absorption | Very poor systemic absorption when taken orally [1.4.1]. Acts locally. | Well-absorbed into the bloodstream, acting systemically throughout the body [1.4.6]. |
| Common Uses | Oral thrush, skin and gut Candida infections [1.4.4]. | Oral thrush, vaginal yeast infections, and serious systemic fungal infections [1.4.6]. |
| Drug Interactions | Very few; primarily with yeast-based probiotics [1.2.5]. | Numerous significant interactions (e.g., with certain statins, blood thinners, and other medications) due to its systemic presence [1.4.6]. |
Taking Nystatin Safely
While nystatin is very safe from an interaction standpoint, always follow these best practices:
- Disclose All Medications: Always provide your doctor and pharmacist with a complete list of all your medications, including prescription drugs, over-the-counter medicines, vitamins, and herbal supplements [1.2.2].
- Follow Dosing Instructions: For oral liquid, this often means swishing the medicine in your mouth for as long as possible before swallowing to maximize contact time with the fungus. Do not eat or drink for 30 minutes after taking it [1.4.6].
- Report Side Effects: The most common side effects are GI-related, such as nausea, stomach pain, or diarrhea, because the drug acts within the gut [1.4.2]. Report any severe or persistent side effects to your healthcare provider.
Conclusion
The answer to 'What drugs cannot be taken with nystatin?' is a very short list. Due to its poor absorption into the bloodstream, nystatin has one of the safest drug interaction profiles of any antifungal. The primary substance to avoid is yeast-based probiotics like Saccharomyces boulardii, as nystatin will negate their effects. Otherwise, it is generally safe to use with most other common medications, from painkillers to antibiotics [1.2.3, 1.2.8]. As with any medicine, open communication with your healthcare provider is the best way to ensure safety and effectiveness.
For further reading, you can review detailed drug information from the National Institutes of Health (NIH).
