Subcutaneous Methotrexate, Ulcers, and Doses

Abstract

with interest the article by Kurian and Haber regarding the use of subcutaneous methotrexate (MTX) and cutaneous ulcerations in a nonpsoriatic patient. 1 Having prescribed oral MTX for psoriasis since 1971, I wondered in 1998 whether administering this drug subcutaneously would be safer for the liver. The major advantage over oral therapy is that only 10% of the subcutaneous dose, that is, that which travels from the inferior vena cava through the heart and then to the hepatic artery, actually achieves ''first pass through the liver.'' By contrast, oral administration exposes the liver, via the portal system, to virtually 100% of the dose. Dr. John Koo (personal communication 1998) agreed that it would be as effective as intramuscular administration, and I have used it exclusively subcutaneously since that time.On the basis of this ''experience-based medicine,'' I can affirm that this works very nicely. The important lesson I have learned over 13 years is that the dose needed is less when administered this way. Indeed, I have never required more than 12.5 mg given subcutaneously weekly for psoriasis. The ulcers apparently generated by 25 mg given subcutaneously to a 67-year-old therefore represent for me an irresistible teaching moment, particularly because the patient was apparently also unsupported with folic acid.The subcutaneous MTX dose in my hands is usually 7.5 mg (0.3 mL of the standard solution) weekly and is provided to the patient in plastic bag ''six-packs'' (Figure 1), with six additional fresh needles for self-injection at home. We charge $5 per syringe.The folic acid standard dose in the United States is 1 to 2 mg daily. We use the latter, but we do miss the (far preferred) 5 mg tablets in Canada.