Methotrexate (Amethopterin [Britain]) is completely and rapidly absorbed in the usual therapeutic dosages. In order to maintain a blood level for approximately 36 hours, small oral doses should be given every eight hours or sooner. Twenty-three of 26 patients had good responses to a regimen of four such doses in a 24-hour period of each week.
Halprin KM, Fukui K, Ohkawara A. Blood Levels of Methotrexate and the Treatment of Psoriasis. Arch Dermatol. 1971;103(3):243-249. doi:10.1001/archderm.1971.04000150013002