- Discussion: 
- prevents conversion of purine bases by suppressing synthesis of guanine and adenosine;

- RA Doses: 1-2.5 mg/kg/day; 
- onset of action is usually 12 to 24 weeks; 
- discontinuation of the drug is marked by a return in disease activity; 
- Toxicity: 
- most common toxicity is gastrointestinal including nausea, anorexia, and, rarely, vomiting and pancreatitis;

- hematologic toxicity including leukopenia, thrombocytopenia, and anemia, may occur and is generally dose dependent. 

Influence of methotrexate and azathioprine on radiologic progression in rheumatoid arthritis. A randomized, double-blind study [see comments.]