If a patient develops allergic contact dermatitis to topical nitrogen mustard, does the treatment have to be permanently discontinued?

No. The medication should be temporarily discontinued, and the dermatitis treated with either topical or systemic steroids. When the dermatitis has cleared, the patient can then be restarted on dilute HN₂. Usually, the patient will tolerate 10 mg of HN₂ in 1 gallon of water. The concentration of the HN₂ can be slowly increased over several months without a flare of the dermatitis. On a rare occasion, a patient may develop immediate contact urticaria to topical HN₂, requiring discontinuation of treatment.