Closed patch test should not be used in the presence of suspected bithionol sensitivity. A contact test, 0.1% or possibly 0.2% bithionol in acetone is adequate with a reading period of two to three days.
GAUL LE. Sensitivity to BithionolThe Need for Caution When Patch Testing This Compound. Arch Dermatol. 1963;87(3):383. doi:10.1001/archderm.1963.01590150099018