(FDA approved in bold)

• Treatment of malignancies, including non-Hodgkin lymphoma, gestational choriocarcinoma, head and neck epidermoid cancer, and lung and breast cancer
  
• Psoriasis
  
• Rheumatoid arthritis
  
• Inflammatory myopathies: polymyositis (PM) and dermatomyositis (DM)
  
• Vasculitis, including Wegener’s granulomatosis
  
• Relapsing-remitting or chronic progressive multiple sclerosis (MS)
  
• Ulcerative colitis or Crohn’s disease
  
• Systemic lupus erythematosus
  
• Psoriatic arthritis

• Inhibits dihydrofolic acid reductase. Prevents synthesis of purine nucleotides and thymodylate. This interferes with DNA synthesis, repair, and replication

• Within a week, but effect on neurological diseases may take months

• DM/PM: improves strength, and may allow discontinuation or reduced dose of corticosteroids. Corticosteroids are tapered first. Taper slowly over 6 months if clinical remission occurs
  
• MS: May reduce relapses and new lesions on MRI
  
• Other disorders: Improves symptoms and clinical markers of the disease

• DM/PM: Question the diagnosis (inclusion-body myositis, hypothyroidism, muscular dystrophy), rule out corticosteroid-induced myopathy, and evaluate for undiagnosed malignancy (especially in DM). Change to azathioprine
  
• MS: If clearly not helpful, change to another agent

• Usually used in combination with corticosteroids (to reduce corticosteroid dose) in DM and PM. Occasionally combined with other treatments for the treatment of MS

• Obtain CBC, liver and renal function tests, and chest x-ray at baseline and at dosage adjustments, or for any clinical symptoms. Use serum level and WBC to assess response to treatment