Thank you for your inquiry.
Unfortunately I am not aware of, and could not find, a desensitization protocol to commonly applied doses used to treat patients with rheumatoid arthritis. However, as you mentioned, there are quite a number of desensitization protocols to methotrexate used in doses for treatment of cancer. One can actually adopt the same principles to a desensitization protocol used for the lower doses designed to treat rheumatoid arthritis. You should be able to accomplish this since this drug is available, as you know, in a liquid for intravenous use.
My suggestion is to start with 1:1,000 to 1:10,000 of the desired amount and progress slowly thereafter with doses administered every hour until the therapeutic dose is reached (using the same principles as one would apply in doing a penicillin desensitization). The venue to be used would be dependent upon your clinical judgment based upon the severity of the preceding reaction.
When you reached a dose of 1 mg, you could switch to the tablet, which is available in a 2.5 mg strength.
Thank you again for your inquiry and we hope this response is helpful to you.
Phil Lieberman, M.D.