Life-Threatening Reaction with Topical 5-Fluorouracil

Area of Science:

• Dermatology
• Pharmacology
• Oncology

Background:

• Topical 5-fluorouracil (5-FU) is a common treatment for actinic keratosis.
• Adverse drug reactions to topical 5-FU can occur, but systemic reactions are rare.

Purpose of the Study:

• To report a case of a severe systemic adverse drug reaction to topical 5-FU.
• To discuss the potential mechanisms and implications of such reactions.

Main Methods:

• Case report of a 67-year-old male patient.
• Clinical observation of adverse events following topical 5-FU application.
• Consultation with Hematology/Oncology.

Main Results:

• Patient developed lethargy, fatigue, fever, mouth erosions, and severe mucositis after 1 week of 0.5% topical 5-FU.
• Systemic side effects necessitated hospitalization due to dehydration and significant weight loss.
• A possible systemic 5-FU reaction, potentially linked to dihydropyrimidine dehydrogenase (DPD) deficiency, was suspected.

Conclusions:

• Topical 5-FU can cause severe systemic adverse drug reactions, mimicking chemotherapy side effects.
• DPD deficiency may predispose patients to severe reactions even with topical 5-FU.
• Further investigation into patient's DPD status was declined, limiting definitive diagnosis.