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Methotrexate

Prescription

Antimetabolite — antineoplastic / Immunosuppressant

Last reviewed 19 Apr 2026 · PetCare.AI Editorial Team

Species

Dog, Cat

Brands

3 available

Interactions

3 documented

Formulations

Mechanism of action

Inhibits dihydrofolate reductase, blocking conversion of dihydrofolate to tetrahydrofolate, thereby inhibiting purine and thymidylate synthesis in rapidly dividing cells

At a glance

Class

Antimetabolite — antineoplastic / Immunosuppressant

Schedule

Prescription

Storage

Store below 25°C, protect from light; handle with gloves (cytotoxic)

Dosing

🐕

Dog

Lymphoma (rescue protocol) / Immune-mediated polyarthritis

Dose

2.5 mg/m²

Route

PO, IV

Frequency

2–3× per week (PO for immunosuppression); high-dose IV per oncology protocol

Max dose

15 mg

Duration: Per protocol; leucovorin rescue with high-dose protocols

🐈

Cat

Lymphoma (rescue protocol)

Dose

2.5 mg/m²

Route

PO, IV

Frequency

2–3× per week

Max dose

5 mg

Duration: Per oncology protocol

Educational reference only

This information is provided for educational purposes and is not a substitute for professional veterinary advice, diagnosis, or treatment. Always consult a qualified veterinarian before administering any medication to your pet. Find a vet near you →

Formulations

💊

Tablet — 1

Strength

2.5mg

Available in India

💉

Injection — 1

Strength

25mg/mL

Available in India

Storage

Store below 25°C, protect from light; handle with gloves (cytotoxic)

Safety

Absolute contraindications — do not use

Renal insufficiency
Renally excreted; nephrotoxic at high doses
Pre-existing bone marrow suppression

Use with caution

Concurrent NSAIDs
Reduced renal clearance of methotrexate

Adverse effects

Common

GI upset

Myelosuppression

Serious

Severe leukopenia

Hepatotoxicity

Nephrotoxicity

GI ulceration

Monitoring parameters

CBC weeklyBUN/CreatinineHepatic enzymes

Educational reference only

Interactions

Contraindicated — 1

Trimethoprim-Sulfamethoxazole

contraindicated

Both are folate antagonists; combined use causes severe bone marrow suppression

Management: Do not combine. If antibiotic needed during methotrexate therapy, use non-folate antagonist.

Major — 2

Meloxicam

major

NSAIDs reduce renal clearance of methotrexate, increasing methotrexate toxicity risk

Management: Avoid NSAIDs during methotrexate therapy. If pain management needed, use opioids.

Metamizole (Dipyrone)

major

Metamizole may reduce renal clearance of methotrexate and both cause bone marrow suppression

Management: Avoid concurrent use during methotrexate therapy. Use opioids for analgesia.

Educational reference only

Brands

International

Rheumatrex

Stada

India

Folitrax

IPCA Labs

Biotrexate

Biochem Pharma

FAQs

Frequently asked questions

›What is Methotrexate?

Methotrexate is a antimetabolite — antineoplastic / immunosuppressant used in pets. Inhibits dihydrofolate reductase, blocking conversion of dihydrofolate to tetrahydrofolate, thereby inhibiting purine and thymidylate synthesis in rapidly dividing cells

›What is Methotrexate used for in pets?

Methotrexate is used in veterinary medicine for: Lymphoma (rescue protocol) / Immune-mediated polyarthritis; Lymphoma (rescue protocol).

›What is the Methotrexate dose for dogs?

For dogs, Methotrexate is typically dosed as follows — Lymphoma (rescue protocol) / Immune-mediated polyarthritis: 2.5 mg/m² PO/IV 2–3× per week (PO for immunosuppression); high-dose IV per oncology protocol. Always consult your veterinarian for a dose tailored to your pet's weight, age, and condition.

›What is the Methotrexate dose for cats?

For cats, Methotrexate is typically dosed as follows — Lymphoma (rescue protocol): 2.5 mg/m² PO/IV 2–3× per week. Always consult your veterinarian for a dose tailored to your pet's weight, age, and condition.

›What are the side effects of Methotrexate?

Common: GI upset, Myelosuppression. Serious (call your vet immediately): Severe leukopenia, Hepatotoxicity, Nephrotoxicity, GI ulceration.

›Does Methotrexate need a prescription?

Yes. Methotrexate is a prescription medication and should only be administered under veterinary supervision.

›When should Methotrexate not be used?

Do not use Methotrexate if: Renal insufficiency; Pre-existing bone marrow suppression.

Educational reference only

References

The PetCare.AI drug reference is built from 13 authoritative sources cited across 580 drug monographs.

Textbooks & handbooks — 5

Plumb's Veterinary Drug Handbook
Withrow & MacEwen's Small Animal Clinical Oncology
Merck Veterinary Manual
NRC Nutrient Requirements of Dogs and Cats
Veterinary Pharmacology and Therapeutics (Riviere & Papich)

Clinical guidelines & consensus — 4

ASPCA Animal Poison Control Center Guidelines
AAHA Diabetes Management Guidelines
ASPCA Poison Control Guidelines
RECOVER CPR Guidelines

Journals & peer-reviewed studies — 2

EPIC Study (J Vet Intern Med 2016)
JVIM FAT CAT Study

Regulatory & approvals — 1

CDSCO Veterinary Drug Approval Registry (1969–2026)

Databases — 1

Washington State University VCPL MDR1 Database

Related medicines

Other medicines in the same class (Antimetabolite).

Fluorouracil (5-FU)

Pyrimidine analog converted to active metabolites that inhibit thymidylate synthase (blocking DNA synthesis) and incorporate into RNA (disrupting RNA processing). S-phase specific.

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