I have a few patients older than 70 and even 80 years with a good long term response to minimal dosage (7.5 mg per week) of Methotrexat. It is not the case in younger patients. I wonder whether is it a matter of pharmacodynamics or pharmacokinetics. Occasionaly I stop MTX when their condition is good, and reintroduce it when it is worse.
According to the opinion of rheumatologists, who have much more experiences with MTX than dermatologists, the cumulative dose should not be a problem.
To follow liver function I use just aminotranspherases.