Azathioprine UV Contraindication — SCE Dermatology MCQ

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ModeratePhotobiologyAzathioprine UV ContraindicationSCE Dermatology

A 30-year-old woman with atopic eczema is being considered for phototherapy. She takes Azathioprine for her eczema. Is NB-UVB phototherapy safe in combination with Azathioprine?

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Correct answer: C — No — the combination of Azathioprine and UV phototherapy is CONTRAINDICATED due to synergistic photocarcinogenic risk (Azathioprine photosensitises DNA to UVA)

Azathioprine should NOT be combined with UV phototherapy. Azathioprine metabolites (6-thioguanine) are incorporated into DNA and photosensitise it to UVA radiation, generating reactive oxygen species and mutagenic DNA damage. This combination creates synergistic photocarcinogenic risk — significantly higher than either agent alone. BAD guidelines specifically contraindicate this combination. Similarly, Ciclosporin should not be combined with phototherapy due to increased skin cancer risk (immunosuppression + UV mutagenesis). If phototherapy is planned, Azathioprine should be stopped beforehand with an appropriate washout period. If systemic immunosuppression is needed alongside phototherapy, Methotrexate (which does not photosensitise DNA) may be a safer option.

Reference: BAD 2019 Phototherapy; BAD Drug Monitoring