Can Synthroid and Nystatin Be Taken Together?
Yes, a patient can safely take Synthroid (levothyroxine) with nystatin—there are no clinically significant drug interactions between these medications.
Key Points
No Drug Interaction Evidence
- Nystatin is a nonabsorbable antifungal agent that acts locally in the gastrointestinal tract and oral mucosa, with minimal to no systemic absorption 1.
- Levothyroxine absorption occurs primarily in the small intestine, and drugs that affect thyroid function or absorption are typically those that alter gastric pH, bind thyroid hormone, or affect thyroid metabolism systemically 2.
- No evidence in the medical literature or clinical guidelines identifies nystatin as interfering with levothyroxine absorption, metabolism, or efficacy 1, 3.
Practical Administration Considerations
- Levothyroxine should be taken on an empty stomach, ideally 30-60 minutes before breakfast, to optimize absorption 4, 5, 6.
- Nystatin suspension for oral thrush is typically administered 4-6 mL (400,000-600,000 units) four times daily, with the patient swishing it in the mouth for at least 2 minutes before swallowing 3.
- These medications can be taken at different times of day without concern for interaction—for example, levothyroxine in the morning on an empty stomach and nystatin doses spread throughout the day 3, 4.
Clinical Context
- Nystatin is commonly used for oral candidiasis (thrush), vulvovaginal candidiasis, and prophylaxis in high-risk neonates 1, 3.
- The nonabsorbable nature of nystatin means it does not enter systemic circulation in meaningful amounts and therefore cannot interact with levothyroxine pharmacokinetics 1.
- Drugs that genuinely affect thyroid function include tyrosine kinase inhibitors, immune modulators, amiodarone, and lithium—nystatin is not among these agents 2.
Monitoring Recommendations
- Continue routine thyroid function monitoring (serum TSH) as clinically indicated for the underlying thyroid condition, typically every 6-12 weeks after dose adjustments and annually once stable 4.
- No additional thyroid monitoring is required specifically due to nystatin co-administration 2, 4.
- Ensure levothyroxine dosing remains consistent with standard absorption optimization practices (empty stomach, separated from interfering substances like calcium, iron, or proton pump inhibitors) 4, 5.
Common Pitfall to Avoid
- Do not unnecessarily separate nystatin from levothyroxine by hours if using nystatin suspension for oral thrush, as this creates an inconvenient dosing schedule without clinical benefit 3, 4.
- The key is maintaining proper levothyroxine administration technique (fasting state), not avoiding nystatin 4, 6.