Joe S. I hope you followed up with whomever ordered that dose of MTX. Even for chemotherapy for malignancy the dose rarely exceeds 30 mg/m2 (that's short for body surface area reached by multiplying body weight in kg by height in meters) and I've never heard of it being given more than once a day, and even then only for about 5 days before the dosing was interrupted.
For an average sized adult (5"5"", 140 lbs) the once a day dose for Choriocarcinoma is approximately 3,000 mg daily for 5 days with a minimal one week break before the next round., and that is the highest dosing, used only for that particular malignancy and for Trophoblastic Disease.
Even if the 50 ml you were prescribed was the pediatric concentration of 10 mg/ml, each vial contained 500 mg, which I'm assuming was given IV. Far more likely it was the 25 mg/ml because the pediatric concentration warnings are very prominent, which would make the total dose/day 2500 mg!
The usual rheumatological dose is approximately 5-10% of the chemotherapy dose.
I must admit it's been several years since I was actively involved in administrating this type of medication, and protocols may have been altered, but when I read your dose, I literally gasped!