Can topical 5‑fluorouracil (Efudix) cause vertigo?

Can Topical 5-Fluorouracil (Efudix) Cause Vertigo?

Topical 5-fluorouracil (Efudix) is not documented to cause vertigo in standard dermatologic use, and this side effect is not listed in the FDA drug label or major clinical guidelines. The expected adverse effects are localized skin reactions including erythema, erosions, crusting, and inflammation at the application site 1.

Expected Side Effects of Topical 5-FU

The FDA-approved drug label for Efudix clearly outlines anticipated adverse reactions, which are predominantly dermatologic 1:

• Local skin reactions: Marked erythema, erosions, crust formation, soreness, and swelling at treatment sites
• Pigmentary changes: Hyperpigmentation or less frequently hypopigmentation with prolonged use
• Irritation: Particularly if applied near eyes, nose, or mouth
• Systemic absorption concerns: Increased absorption may occur through ulcerated or inflamed skin

Vertigo is not mentioned as a known adverse effect in the comprehensive FDA labeling 1.

Rare Systemic and Neurologic Toxicities

While topical 5-FU is generally considered safe with primarily local effects, emerging case reports document rare systemic toxicities:

Documented Neurologic Effects (Not Including Vertigo)

• Focal neurotoxicity: One 2024 case report described supraorbital neuralgia with focal paralysis, sensory loss, and paresthesias after topical 5-FU application to the scalp 2
• Severe neutropenia: Documented after topical application, particularly in patients with dihydropyrimidine dehydrogenase (DPD) deficiency 3
• Peripheral neuropathy exacerbation: Reported in rare cases 3

Systemic 5-FU and Neurovascular Effects

When administered systemically (intravenous chemotherapy), 5-FU can cause:

• Cerebral vasospasm with stroke-like symptoms 4
• Acute cerebellar syndrome 3
• Headaches 3

However, these neurologic complications are associated with systemic chemotherapy doses, not topical dermatologic formulations.

Ototoxicity Considerations

One animal study examined whether topical 5-FU affects inner ear function in guinea pigs 5:

• Application to the external ear canal was safe with no effect on endocochlear potential
• Application to the middle ear showed some ototoxic risk (statistically significant changes in endocochlear potential)

This suggests that standard topical application to intact skin should not affect vestibular function or cause vertigo, as the drug does not reach the inner ear structures.

Clinical Context and Differential Diagnosis

If a patient using topical Efudix reports vertigo, consider:

1. Coincidental timing: Vertigo from other causes (benign paroxysmal positional vertigo, vestibular migraine, cerebrovascular disease) 6
2. Medication interactions: Review all concurrent medications
3. Systemic absorption: Only plausible if applied to large surface areas (>500 cm²) or extensively ulcerated skin 7
4. DPD deficiency: Rare genetic condition causing impaired 5-FU metabolism, leading to toxic accumulation even from topical use 2, 3

Practical Recommendations

For patients using topical 5-FU who develop vertigo:

• Investigate alternative causes of vertigo first, as this is not a recognized side effect
• Assess for signs of systemic toxicity (severe neutropenia, neurologic symptoms beyond vertigo)
• Consider DPD deficiency testing only if multiple systemic symptoms develop
• Discontinue 5-FU temporarily if severe systemic symptoms emerge

The evidence strongly suggests topical Efudix does not cause vertigo through standard dermatologic application to intact skin.