Methotrexate
Generic Details
Generic Name
Methotrexate
Other Names
- Amethopterin
Drug Class
- Antimetabolite
- Antineoplastic
Chemical Formula
C20H22N8O5
Molecular Weight
454.44 g/mol
Mechanism of Action
- Inhibition of dihydrofolate reductase
- Antagonism of folate metabolism
Indications
- Rheumatoid arthritis
- Psoriasis
- Cancer (leukemias, lymphoma)
Common Dosage Forms
- Tablet
- Injection
- Oral solution
Typical Dosage
- 15-25 mg once weekly for rheumatoid arthritis
- 5-25 mg once weekly for psoriasis
Pediatric Dosage
- Rheumatoid arthritis: 10-15 mg/m2 once weekly
Geriatric Dosage
- Adjust dosage based on renal function and liver enzymes
Side Effects
- Nausea
- Vomiting
- Mouth sores
- Diarrhea
- Liver toxicity
- Bone marrow suppression
Contraindications
- Pregnancy
- Breastfeeding
- Liver disease
- Immunodeficiency
Pregnancy Category
- Category X - Contraindicated
Lactation Safety
- Not recommended during breastfeeding
Drug Interactions
- NSAIDs
- Probenecid
- Trimethoprim-sulfamethoxazole
Overdose Symptoms
- Severe vomiting
- Mucositis
- Renal failure
Antidote for Overdose
- Leucovorin (Folinic acid)
Storage Conditions
- Store at room temperature (15-30°C)
Pharmacokinetics
- Absorption: Well absorbed after oral administration
- Distribution: Enters cerebrospinal fluid; crosses the placenta
- Metabolism: Hepatic metabolism
- Excretion: Primarily renal excretion
Precautions
- Monitor liver function tests
- Monitor blood counts regularly
Warnings
- Increased risk of infections
- Increased risk of lymphomas
Others
- Methotrexate should be used with caution in patients with renal impairment.