Methotrexate

Introduction Overview

Generic Name

methotrexate

Brand Name

Trexall, Xatmep, Jylamvo

Dosage Form

oral, injectable

Drug Class

Antimetabolites, Antipsoriatics, Antirheumatics, Other immunosuppressants

Pharmacokinetics

Absorption:
Methotrexate is administered primarily by oral and parenteral routes. Oral methotrexate exhibits variable and incomplete absorption, especially at higher doses; bioavailability decreases as the dose increases. Peak plasma concentrations typically occur 1 to 2 hours post oral administration. Food intake may delay absorption but does not significantly affect bioavailability. Sublingual and intramuscular administrations are alternatives to enhance bioavailability in cases of malabsorption or intolerance to oral forms.

Distribution:
Following absorption, methotrexate distributes widely into body tissues including kidney, liver, skin, and lungs. It penetrates synovial fluid, cerebrospinal fluid (CSF), and ascitic and pleural fluids, but CSF penetration is limited at low doses. Methotrexate binds variably to plasma proteins, primarily albumin, with about 50% protein binding at therapeutic levels. Tissue retention and intracellular polyglutamation prolong its pharmacologic effects beyond plasma elimination.

Metabolism:
Methotrexate undergoes limited hepatic metabolism. The primary metabolic pathway is conversion to 7-hydroxymethotrexate, which retains some pharmacologic activity and is less soluble. Polyglutamated forms of methotrexate accumulate intracellularly and are responsible for sustained activity within target cells. Metabolic pathways do not extensively involve cytochrome P450 enzymes, reducing potential for major drug-drug interactions via this mechanism.

Elimination:
Methotrexate is predominantly excreted unchanged via renal glomerular filtration and active tubular secretion. Approximately 80%-90% of the dose is eliminated in urine within 24 hours in patients with normal renal function. Renal impairment significantly prolongs methotrexate elimination half-life and increases toxicity risk. Biliary excretion is minimal, though some enterohepatic recirculation may occur. Methotrexate has a half-life ranging from 3 to 10 hours depending on dose and renal function. Monitoring renal function is critical during therapy to adjust dosing and prevent accumulation.

Dosage Forms

Available Dosage Forms:
Methotrexate is available in multiple formulations to accommodate various indications and patient needs:
- Oral Tablets: commonly 2.5 mg strength.
- Oral Liquid (Xatmep): available in 2.5 mg/5 mL suspension.
- Subcutaneous injection (Otrexup, Rasuvo): prefilled auto-injectors with variable doses.
- Intramuscular injection: methotrexate sodium injectable solutions.
- Intravenous injection: used for high-dose chemotherapy regimens.

Dosages for Adults and Adolescents:
Dosing varies substantially according to indication. For rheumatoid arthritis and psoriasis, typical doses range from 7.5 to 25 mg once weekly. In oncology, dosing is higher and can be administered daily, weekly, or in cycles, often requiring leucovorin rescue to mitigate toxicity. Pediatric dosing for juvenile rheumatoid arthritis depends on body surface area with typical doses of 10-15 mg/m2 weekly.

Specific Patient Populations:
In patients with renal impairment, doses must be reduced and dosing intervals prolonged due to decreased clearance. Methotrexate use is contraindicated or extremely cautious in patients with chronic liver disease, bone marrow suppression, or during pregnancy except for certain cancers under close supervision. The dosing frequency for arthritis and psoriasis is generally once weekly to minimize toxicity risks, emphasizing the critical importance of adhering to prescribed schedules and not taking the medication daily without physician oversight.

Mechanism Of Action

Methotrexate is a folate analog that acts as a potent inhibitor of dihydrofolate reductase (DHFR), an essential enzyme in the tetrahydrofolate synthesis pathway. By binding to DHFR, methotrexate blocks the reduction of dihydrofolate to tetrahydrofolate, which is necessary for the synthesis of thymidylate and purine nucleotides required for DNA and RNA synthesis. This inhibition results in disruption of cellular replication, preferentially affecting rapidly proliferating cells such as malignant cells, immune cells, and those of the skin.

Intracellularly, methotrexate is converted to polyglutamated derivatives, which prolong its retention within cells and enhance inhibition of not only DHFR but also other enzymes involved in folate metabolism such as thymidylate synthase and AICAR transformylase. This leads to an accumulation of adenosine, an anti-inflammatory mediator, which partly explains methotrexate's immunosuppressive and anti-inflammatory effects beneficial in autoimmune diseases like rheumatoid arthritis and psoriasis.

Methotrexate's induction of apoptosis in activated T cells and suppression of interleukin production contribute to its ability to reduce inflammation and inhibit immune-mediated tissue damage. Compared to other antimetabolites, methotrexate has a relatively selective toxicity profile, enabling its use in lower doses for immunomodulation as opposed to the high doses used in oncology.

Clinically, methotrexate's dual action—antiproliferative in cancer and anti-inflammatory in autoimmune disease—underscores its versatility. Research continues to elucidate additional mechanisms including effects on adenosine receptor pathways and modulation of cytokine profiles, enhancing our understanding of its broad therapeutic applications.

Pharmacological Actions

Inhibition of dihydrofolate reductase enzyme, leading to decreased DNA, RNA, and protein synthesis.
Antiproliferative effects on rapidly dividing malignant cells and immune cells.
Immunosuppressive activity through induction of apoptosis in activated T lymphocytes.
Anti-inflammatory effects mediated by increased extracellular adenosine concentrations.
Inhibition of enzymes involved in folate metabolism beyond DHFR, including thymidylate synthase and AICAR transformylase.
Reduction of pro-inflammatory cytokine production, such as interleukins and tumor necrosis factor-alpha.
Modulation of immune system responses beneficial in autoimmune diseases like rheumatoid arthritis and psoriasis.
Selective toxicity allows differentiation between malignant and normal cells in various tissues.
Contributes to decreased keratinocyte proliferation in severe psoriasis.
Leads to cell cycle arrest in S-phase in susceptible cells.
Polyglutamation enhances duration of action and intracellular retention.
Can cross-react with folate pathways affecting nutrient metabolism.
Mechanisms extend to both antiproliferative and immunomodulatory effects depending on dose.
Potential effects on adenosine receptor signaling contributing to anti-inflammatory action.

Therapeutic Or Clinical Uses

Treatment of various malignancies including acute lymphoblastic leukemia, breast cancer, lung cancer, head and neck cancers, and uterine cancer.
Management of severe psoriasis unresponsive to topical therapies.
Treatment of rheumatoid arthritis to reduce inflammation and prevent joint damage.
Control of active polyarticular-course juvenile rheumatoid arthritis in pediatric patients.
Adjunct therapy in certain lymphomas and other hematologic malignancies.
Used in chemotherapy regimens both as single agent and in combination protocols.
Immunosuppressive therapy for autoimmune disorders beyond rheumatoid arthritis and psoriasis in off-label uses.
Treatment of ectopic pregnancy (off-label low-dose usage).
Reduction of inflammation in psoriatic arthritis.
Management of Crohn’s disease and other inflammatory bowel conditions in experimental contexts.
Therapy for other dermatologic and rheumatologic conditions where immunosuppression is warranted.
Used in low doses for maintenance therapy in autoimmune diseases.
Utilized in cases where other immunosuppressants have failed or are contraindicated.
Employed cautiously in pregnancy for cancer treatment when benefits outweigh risks.
Investigated for novel indications including certain chronic inflammatory disorders.

Side Or Adverse Effects

Common side effects include fever, fatigue, and malaise.
Myelosuppression leading to low blood cell counts causing anemia, leukopenia, and thrombocytopenia.
Mouth ulcers and stomatitis.
Gastrointestinal disturbances such as nausea, vomiting, and abdominal pain.
Abnormal liver function tests and hepatotoxicity, which can progress to fibrosis or cirrhosis.
Hair loss (alopecia).
Photosensitivity and burning skin lesions.
Respiratory symptoms including cough, dyspnea, and potential pneumonitis.
Severe hypersensitivity reactions including anaphylaxis and Stevens-Johnson syndrome.
Renal toxicity manifesting as decreased urine output and kidney injury.
Neurological effects including headache, dizziness, seizures, and cognitive disturbances.
Infections due to immunosuppression.
Tumor lysis syndrome signs such as muscle cramps, arrhythmias, and electrolyte abnormalities.
Hepatic fibrosis and cirrhosis with long-term use, especially with concomitant alcohol use.
Potential teratogenicity and fetal toxicity leading to pregnancy loss or congenital anomalies.

Precautions

Use cautiously in patients with pre-existing liver disease or alcoholism due to increased risk of hepatotoxicity.
Monitor blood cell counts frequently to detect bone marrow suppression early.
Avoid use in patients with compromised renal function unless doses are appropriately adjusted.
Strict adherence to dosing schedule is critical; avoid daily dosing unless specifically prescribed.
Avoid live vaccines during treatment due to risk of severe infections.
Use effective contraception during treatment and post-treatment period for both males and females.
Close monitoring during pregnancy; contraindicated for arthritis or psoriasis treatment but may be used for cancer under supervision.
Avoid alcohol consumption to mitigate liver damage risk.
Caution in patients with pulmonary disease as methotrexate can cause pneumonitis.
Regular liver function tests and periodic liver biopsies may be warranted for long-term therapy.
Patients should avoid excessive sun exposure and use sun protection.
Dose adjustments are necessary in the elderly and debilitated patients.
Disclose all concomitant medications to avoid harmful interactions.
Patients should be educated on signs of toxicity and advised to report symptoms promptly.
Avoid use in breastfeeding due to potential adverse effects in infants.

Warnings

Methotrexate can cause severe, sometimes fatal, bone marrow suppression.
Risk of hepatotoxicity requiring regular liver function monitoring; cumulative liver damage possible.
Methotrexate use during pregnancy can cause fetal death and congenital malformations.
Potential for severe pulmonary toxicity including interstitial pneumonitis.
Fatal mucositis and gastrointestinal ulceration have been reported, especially with high-dose therapy.
Serious and life-threatening infections may occur due to immunosuppression.
High risk of toxicity with incorrect daily dosing in conditions requiring weekly administration.
Increased risk of renal toxicity necessitating dose adjustment in renal impairment.
Concomitant use with NSAIDs, antibiotics, or proton pump inhibitors can increase methotrexate toxicity.
Rare but severe skin reactions including toxic epidermal necrolysis and Stevens-Johnson syndrome.
May cause neurotoxicity including seizures and coma in high doses or intrathecal use.
Avoid use in patients with low blood cell counts or severe immunodeficiency.
Requires adequate hydration and urine alkalinization in high-dose protocols to prevent renal damage.
Careful monitoring required during concomitant radiotherapy to avoid enhanced toxicity.
Patient death has been reported with dosing errors or overdose.

Contraindication

Known hypersensitivity to methotrexate or any component of its formulation.
Pregnancy when used for treatment of psoriasis or rheumatoid arthritis.
Severe bone marrow suppression or leukopenia.
Significant chronic liver disease including cirrhosis or severe hepatic impairment.
Immunodeficiency states or severe infections.
Alcoholism or active alcoholic liver disease.
Severe renal impairment without appropriate dose adjustment.
Pre-existing blood dyscrasias or bone marrow disorders.
Concurrent use with live vaccines.
Hypersensitivity to other folate antagonists if cross-reactivity suspected.
Patients unable to comply with monitoring requirements or avoid contraindicated substances.
Breastfeeding mothers due to risk to the infant.
Patients with untreated folate deficiency.
Concomitant use with medications that severely impair methotrexate clearance without monitoring.
Active ulcerative or severe peptic ulcer disease.

Drug Interactions

Concomitant use with NSAIDs (e.g., aspirin, ibuprofen, naproxen) increases risk of methotrexate toxicity due to reduced renal elimination.
Proton pump inhibitors and H2 receptor antagonists can decrease methotrexate clearance, enhancing toxicity risk.
Certain antibiotics (e.g., penicillins, sulfonamides) may impair renal excretion of methotrexate increasing serum levels.
Interaction with folic acid supplements can reduce methotrexate efficacy but may decrease adverse effects; requires careful monitoring.
Concurrent mercaptopurine use can enhance myelosuppressive effects.
Theophylline levels may be elevated due to methotrexate interference with its metabolism.
Trimethoprim and other folate antagonists may produce additive toxicity.
Live vaccines are contraindicated due to risk of infection and reduced vaccine efficacy.
Probenecid and other drugs competing for renal tubular secretion can reduce methotrexate excretion.
Interactions with sulfonylureas may alter blood glucose control.
Concurrent use with chemotherapy agents may increase hematologic toxicity.
Loop diuretics and nephrotoxic agents increase risk of renal impairment when combined with methotrexate.
Cholestyramine may reduce absorption and efficacy of oral methotrexate.
Concomitant use with corticosteroids may mask infection symptoms but also modulate inflammatory response.
Methotrexate may alter phenytoin and digoxin serum concentrations.

Preparations Of The Drug

Oral tablets available most commonly at 2.5 mg strength for systemic administration.
Oral suspension (Xatmep) formulated as 2.5 mg/5 mL for pediatric and patients with swallowing difficulties.
Prefilled subcutaneous auto-injectors (Otrexup, Rasuvo) for convenient administration of precise doses.
Intramuscular and intravenous injectable solutions formulated in multiple concentrations for oncology and autoimmune disease use.
Methotrexate sodium injectable preparations supplied with detailed instructions for dilution and administration.
Packaging designed to protect drug from moisture and light to maintain stability.
Prefilled syringes and pen injector devices to improve adherence and reduce administration errors.
Commercially available as single-agent products and in combination chemotherapy regimens.
Storage requirements include room temperature for tablets and refrigerated conditions for some injectable formulations like Xatmep.
Instructions emphasize careful measurement of oral liquid using provided syringes to ensure accurate dosing.
Unit-dose packaging utilized to safeguard against dosing mistakes in hospital settings.
Parenteral forms intended for administration by healthcare professionals with appropriate monitoring.
Additional formulations under investigation to optimize delivery and minimize toxicity.
Medicinal products are available under various brand names depending on region and manufacturer.
Detailed patient information leaflets accompany preparations for guidance on usage, side effects, and precautions.