Pharm

Methotrexate

search

Methotrexate, Amethopterin, MTX

  • Mechanism
  1. Antimetabolite Chemotherapy (Cell Cycle Specific)
    1. S-Phase toxin (DNA synthesis phase)
  2. Folic Acid structural analog
    1. Competitively inhibits at DHF Reductase
  3. Inhibits de novo Pyrimidine synthesis
  • Dosing
  1. Co-administer Folic Acid 1 mg orally daily (or 5-7 mg once weekly)
    1. Reduces adverse effects (Vomiting, Stomatitis, hepatotoxicity)
    2. Does not decrease Methotrexate efficacy
  2. Rheumatoid Arthritis
    1. Range: 7.5 - 20 mg/week PO, SQ, IM
      1. Taken one day per week either in one dose or in a split dose, 12 hours apart
      2. Have the patient choose a day of the week for the medication to be taken and specify that day on the prescription (e.g. Monday)
    2. Initial: 10 mg per week (5 mg orally twice daily every Monday)
    3. Lowest effective dose: 7.5 mg orally once daily every Monday AM
    4. Average dose: 10 mg orally twice daily every Monday
    5. Maximum dose: 12.5 mg orally twice daily every Monday
  3. Cancer Chemotherapy
    1. Oral: 2.5 to 5 mg/day
    2. Intrathecal: 10 mg weekly to biweekly
  • Efficacy
  1. Rheumatoid Arthritis
    1. Very effective (>85% initially)
    2. Response in 4-6 weeks (faster than other DMARDs)
  2. Curative in Choriocarcinoma
  • Adverse Effects
  1. Oral and Gastrointestinal (most common)
    1. Nausea
    2. Oral Ulcers
    3. Stomatitis
    4. Diarrhea
  2. Hepatic
    1. Hepatic fibrosis
    2. Elevated transaminases
    3. Cirrhosis
  3. Pulmonary
    1. Pulmonary fibrosis or infiltrates
    2. Hypersensitivity Pneumonitis
      1. Presents with dry cough, fever, Dyspnea on exertion
      2. Stop Methotrexate and exclude infection
      3. Start high dose Corticosteroids
      4. Consider gallium lung scan
  4. Neuropsychiatric
    1. Dysphoria
  5. Hematologic
    1. Minimal Immunosuppression
      1. Contrast with Imuran, Cytoxan, Sandimmune
    2. Myelosuppression
    3. Thrombocytopenia
  • Cost
  1. Very expensive (>$1000 per year)
  • Monitoring
  1. Baseline screening
    1. Complete Blood Count with Platelet Count
    2. Recent Chest XRay
    3. Liver Function Tests
      1. Aspartate Aminotransferase (AST)
      2. Alanine Aminotransferase (ALT)
      3. Alkaline Phosphatase
      4. Albumin
      5. Consider Hepatitis B and Hepatitis C serologies
    4. Renal Function Tests
      1. Creatinine
  2. Follow-up Monitoring: (monthly x3, then every 8 weeks)
    1. Complete Blood Count with Platelet Count
    2. Liver Function Tests
      1. Aspartate Aminotransferase (AST)
      2. Alkaline Phosphatase
    3. Renal Function Tests
      1. Creatinine
  3. Liver Biopsy Indications
    1. Cumulative Methotrexate dose >8 gram
    2. Prior heavy Alcohol use
    3. Persistently elevated AST (SGOT) 2-3x normal
    4. Psoriatic Arthritis
  • Contraindications
  • Absolute
  • Contraindications
  • Relative (due to hepatotoxicity)
  1. Alcohol Use
  2. Pre-existing liver disease
  3. Diabetes Mellitus
  4. Obesity
  5. Age >70 years
  • Management
  • Antidote in toxicity
  1. Effects reversed by Leucovorin (Citrovorum factor)
  • Drug Interactions
  • Agents that increase Methotrexate levels
  1. Antibiotics (hold Methotrexate dose until antibiotic course completed)
    1. Sulfa antibiotics (e.g. Trimethoprim Sulfamethoxazole)
    2. Cephalosporins
    3. Penicillins
  2. Proton Pump Inhibitors
    1. May decrease Methotrexate (and metabolite) renal clearance and result in toxic levels
    2. Hold Proton Pump Inhibitors for a few days before and after high dose Methotrexate infusions
    3. Consider use of an H2 Blocker in place of a Proton Pump Inhibitor
    4. Exercise caution in chronic lower dose Methotrexate with Proton Pump Inhibitors
      1. Risk of toxicity increases with concurrent NSAIDs and Aspirin (also decrease Methotrexate renal clearance)
      2. Decrease Methotrexate dose if mild toxicity signs occur
      3. Stop Methotrexate for severe toxicity (e.g. Bone Marrow toxicity)
    5. References
      1. (2012) Presc Lett 19(12): 72