What topical treatments are recommended for a burning rash caused by 5-fluorouracil (5-FU)?

Management of Burning Rash from 5-Fluorouracil Use

For a burning rash caused by 5-fluorouracil (5-FU) treatment, topical low to moderate strength corticosteroids are recommended as the first-line treatment to reduce inflammation and discomfort. 1

Understanding 5-FU Skin Reactions

5-Fluorouracil works by inhibiting thymidylate synthetase, which is needed for DNA synthesis, selectively targeting rapidly dividing cells. This mechanism causes:

• Inflammation of both visible and subclinical lesions
• Erythema (redness) in treated areas
• Progression to crusting, oozing, and soreness with continued application 2

Local skin reactions occur in >90% of patients and are considered an expected extension of the drug's pharmacological activity 2.

Treatment Algorithm for 5-FU Induced Rash

First-Line Treatment:

1. Topical low/moderate strength corticosteroids applied twice daily to affected areas 1

   • Examples: hydrocortisone 1%, triamcinolone 0.1%
   • Apply until inflammation subsides

2. Petrolatum jelly (Vaseline) application

   • Significantly improves skin hydration and reduces erythema 3
   • Apply liberally to affected areas 2-3 times daily

For Moderate to Severe Reactions:

1. Temporarily interrupt 5-FU treatment if reaction is grade 3 or intolerable grade 2 1

   • Resume once reaction improves to grade 0-1

2. Consider systemic corticosteroids for severe reactions

   • Prednisone 0.5-1 mg/kg body weight for 7 days 1

For Persistent or Worsening Reactions:

1. Reassess after 2 weeks of treatment 1
2. Consider oral antibiotics if superinfection is suspected
   • Doxycycline 100 mg twice daily OR
   • Minocycline 50 mg twice daily OR
   • Oxytetracycline 500 mg twice daily 1

Special Considerations

Distant Reactions

Be aware that 5-FU can occasionally cause distant skin reactions, such as seborrheic dermatitis-like eruptions on the face even when applied elsewhere 4. These reactions typically resolve after discontinuation of 5-FU.

Monitoring for Systemic Effects

Though rare, monitor for signs of systemic toxicity such as:

• Neutropenia
• Taste alterations
• Neurologic symptoms 5

Prevention Tips

• Apply emollients regularly to maintain skin barrier function
• Avoid additional irritants (harsh soaps, alcohol-based products)
• Use sun protection consistently during and after treatment 2

Pitfalls to Avoid

1. Don't continue 5-FU application if severe reactions develop without medical consultation
2. Don't confuse expected inflammatory reaction with allergic reaction or infection
3. Avoid applying high-potency steroids for prolonged periods, especially on the face
4. Don't ignore distant skin reactions as they may be related to 5-FU use 4
5. Avoid applying 5-FU to large areas (>500 cm²) due to potential systemic absorption 2

Remember that some degree of skin reaction is expected and indicates the medication is working. However, severe reactions require medical attention and possible adjustment of the treatment regimen.