Terbinafine Use in Pregnancy: Safety Assessment
Terbinafine is relatively safe for use during pregnancy, classified as FDA Pregnancy Category B, with recent high-quality evidence showing no increased risk of major malformations or spontaneous abortion. However, because fungal infections are rarely life-threatening and treatment can typically be postponed, it is generally recommended to delay therapy until after pregnancy completion when possible 1.
Evidence-Based Safety Profile
FDA Classification and Guideline Recommendations
The FDA classifies terbinafine as Pregnancy Category B, meaning animal reproduction studies have shown no evidence of fetal harm, though adequate human studies are limited 1. The FDA label explicitly states: "it is not expected to harm an unborn baby" but recommends against initiating treatment during pregnancy because onychomycosis treatment can be postponed 2.
Recent High-Quality Human Data
The most robust evidence comes from a 2020 Danish nationwide registry study examining 1,650,649 pregnancies, which found 3:
No increased risk of major malformations:
- Oral terbinafine vs unexposed: OR 1.01 (95% CI 0.63-1.62)
- Topical terbinafine vs unexposed: OR 1.08 (95% CI 0.81-1.44)
No increased risk of spontaneous abortion:
- Oral terbinafine vs unexposed: HR 1.06 (95% CI 0.86-1.32)
- Topical terbinafine vs unexposed: HR 1.04 (95% CI 0.88-1.21)
A 2022 systematic review corroborated these findings, showing absence of increased risk for congenital malformations, spontaneous abortion, preterm birth, small for gestational age, low birth weight, or stillbirth 4.
Clinical Decision Algorithm
When Terbinafine May Be Considered:
Life-threatening fungal infections (e.g., disseminated sporotrichosis): Use amphotericin B as first-line; terbinafine may be discussed for cutaneous/lymphocutaneous disease 2
Non-life-threatening infections (onychomycosis, tinea):
Contraindications During Pregnancy:
- Azole antifungals (itraconazole, fluconazole) are contraindicated due to teratogenic potential 2, 6
- SSKI (saturated solution of potassium iodide) is contraindicated due to fetal thyroid toxicity 2
Important Caveats and Pitfalls
Breastfeeding Considerations
Terbinafine passes into breast milk at a milk-to-plasma ratio of 7:1 1. The FDA label states "treatment with terbinafine is not recommended in nursing mothers" 1. Mothers should discuss risks/benefits with their physician before use during lactation 2.
Rare but Serious Adverse Events
While not pregnancy-specific, one case report documented terbinafine-induced toxic epidermal necrolysis in a pregnant woman, though with good pregnancy outcomes 7. This underscores the importance of monitoring for serious skin reactions.
Topical vs. Oral Formulations
Topical terbinafine has even more reassuring safety data due to minimal systemic absorption 5. For superficial infections amenable to topical therapy, this route is preferred during pregnancy 5.
Context of Infection Severity
The guideline emphasis on delaying treatment reflects that dermatophyte infections do not disseminate to the fetus, nor are they worsened by pregnancy 2. This makes postponement a reasonable strategy for non-urgent cases.
Practical Recommendations
For pregnant patients requiring antifungal therapy:
- First-line for life-threatening systemic infections: Amphotericin B (safe in pregnancy) 2
- For superficial infections requiring treatment: Topical terbinafine or topical azoles (clotrimazole, miconazole) 5
- For oral therapy when necessary: Terbinafine appears safer than oral azoles based on current evidence 4, 3
- Optimal strategy for onychomycosis: Wait until after pregnancy and breastfeeding completion 1
The emerging evidence suggests current FDA recommendations may be overly cautious 4, but the principle of avoiding unnecessary medication exposure during pregnancy—especially when treatment can be safely deferred—remains sound clinical practice.