Veterinary Drug Handbook (VDH) is the reference veterinarians turn to when they want an independent source of information on the drugs that are used in veterinary medicine today.


Doses - METHOTREXATE, METHOTREXATE SODIUM

Dosages of methotrexate sodium are expressed in terms of methotrexate as are the dosageforms. For more information, refer to the protocol references found in the appendix or otherprotocols found in other small animal medicine texts.

Dogs:

For susceptible neoplastic diseases (usually as part of a multi-drug protocol):
a) 2.5 mg/m2 PO daily (Rosenthal 1985)
b) For malignant lymphoma: 5 mg/m2 on days 1 and 5 of a weekly maintenance schedule.(Coppoc 1988)
c) 2.5 mg/m2 PO 2-3 times weekly; 0.3 - 0.8 mg/m2 IV every 7 days. (O'Keefe and Harris1990)
d) "High dose therapy": 5 - 10 mg/m2 PO, IV, IM or intrathecally followed 2-4 hourslater with leucovorin at 3 mg/m2."Normal dose therapy": 2.5 mg/m2 once daily. Adjust dosage/frequency according totoxicity. (Thompson 1989a)
e) For lymphoma (as part of protocol¯see reference): 0.5 mg/kg IV (maximum dose 25mg) on day 14. (Matus 1989)
f) 2.5 mg/m2 PO daily. (MacEwen and Rosenthal 1989)
g) In combination with other antineoplastics (per protocol) 5 mg/m2 PO twice weekly or0.8 mg/kg IV every 21 days; alternatively 2.5 mg/m2 PO daily. (USPC 1990)

Cats:

For susceptible neoplastic diseases (usually as part of a multi-drug protocol):
a) 2.5 mg/m2 PO 2-3 times weekly; 0.3 - 0.8 mg/m2 IV every 7 days. (O'Keefe and Harris1990)
b) For lymphoma (as part of protocol¯see reference): 0.8 mg/kg IV on day 14 with 5 mgprednisone bid PO. (Matus 1989)
c) For lymphosarcoma: 2.5 - 5 mg/m2 PO 2 - 3 times per week.
For carcinomas and some sarcomas: 10 - 15 mg/m2 every 1-3 weeks. (Couto 1989b)
d) In combination with other antineoplastics (per protocol) 5 mg/m2 PO twice weekly.(USPC 1990)
Monitoring Parameters - 1. Efficacy; 2. Toxicity: a) Monitor for clinical signs and symptoms of
GI irritation and ulceration. b) Complete blood counts (with platelets) should be performed weeklyearly in therapy and eventually every 4-6 weeks when stabilized. If WBC is < 4000/mm3 or plateletcount is <100, 000/mm3 therapy should be discontinued. c) Baseline renal function tests. Continueto monitor if abnormal. d) Baseline hepatic function tests. Monitor liver enzymes on a regular basisduring therapy.
Client Information - Clients must be briefed on the possibilities of severe toxicity developingfrom this drug, including drug-related mortality. Clients should contact the veterinarian should thepatient exhibit any symptoms of profound depression, abnormal bleeding (including bloodydiarrhea) and/or bruising. Wear gloves when administering tablets (particularly if crushed or split); if gloves are not used, wash hands thoroughly after handling tablets.
Dosage Forms/Preparations/FDA Approval Status/Withholding Times - Veterinary-Approved Products: None

Human-Approved Products:

Methotrexate Sodium Oral Tablets (scored) 2.5 mg; Methotrexate® (Immunex), Rheumatrex® &
Rheumatrex Dose Pack® (Lederle) (Rx)
Methotrexate Sodium Injection 2.5 mg/ml in 2 ml vials and 25 mg/ml in 2, 4, 8, & 10 ml vials;
Methotrexate (Lederle), generic; (Rx). Also available in preservative-free 25 mg/ml formulations: Folex®PFS (Adria), Methotrexate LPF® (Lederle); (Rx)
Methotrexate Powder for Injection in 20 mg/vial, 50 mg/vial, and 1 g vials for reconstitution; (Rx)