Six adult men with severe and disabling pityriasis rubra pilaris (PRP) were treated with methotrexate by intermittent intravenous, intermittent intramuscular, intermittent weekly oral, and long-term daily oral administration. The most efficacious method was found to be long-term daily oral administration of methotrexate, alternating 5 mg one day and 2.5 mg the next day without a rest period, even for several months. Three of the six cases cleared in the relatively short treatment times of 12 to 16 weeks. All six cases remained clear after prolonged daily oral administration of methotrexate was discontinued. Increased drug toxicity was not observed within treatment times studied. Anhidrosis present in areas of active PRP was found to clear when the skin reverted to normal. A photosensitive response was seen in three patients after exposure to varying amounts of sunshine.
Knowles WR, Chernosky ME. Pityriasis Rubra PilarisProlonged Treatment With Methotrexate. Arch Dermatol. 1970;102(6):603-612. doi:10.1001/archderm.1970.04000120021004