XATMEP
Clinical safety rating: caution
Comprehensive clinical and safety monograph for XATMEP (XATMEP).
Methotrexate is a folate analog that inhibits dihydrofolate reductase, blocking the synthesis of tetrahydrofolate and thereby inhibiting DNA synthesis and cell proliferation. It also has immunosuppressive and anti-inflammatory effects through inhibition of purine metabolism and adenosine accumulation.
| Metabolism | Primarily hepatic metabolism via aldehyde oxidase and xanthine oxidase to 7-hydroxymethotrexate; minor metabolism via CYP450 enzymes. Polyglutamation occurs intracellularly, enhancing retention and activity. |
| Excretion | Methotrexate is primarily eliminated renally via glomerular filtration and active tubular secretion. Approximately 80-90% of the dose is excreted unchanged in urine within 24 hours. Fecal excretion is minimal (<10%), with biliary elimination accounting for a small fraction. |
| Half-life | The terminal elimination half-life of methotrexate is approximately 3-10 hours for low doses (<50 mg/m²) and 8-15 hours for high doses (≥500 mg/m²). Prolonged half-life (>24 hours) is associated with renal impairment and drug accumulation, increasing toxicity risk. |
| Protein binding | Approximately 50% bound to albumin, primarily to albumin with some binding to other proteins. Binding is saturable; elevated bilirubin or uremia can displace methotrexate, increasing free fraction. |
| Volume of Distribution | Volume of distribution is approximately 0.4-0.8 L/kg for low doses and up to 0.6-1.0 L/kg for high doses. Distribution is extensive into third-space fluid collections (pleural, ascitic), which can act as reservoirs, prolonging elimination. |
| Bioavailability | Oral bioavailability is dose-dependent: ~60% for doses <30 mg/m², decreasing to <20% for doses >80 mg/m² due to saturable absorption. Subcutaneous administration yields nearly 100% bioavailability with less variability. Intramuscular and intravenous routes provide complete bioavailability. |
| Onset of Action | Oral: Clinical effect (e.g., immunosuppression) begins within 3-6 weeks. Subcutaneous: Onset within 2-4 weeks. Intravenous: Onset within hours to days for antineoplastic effect; peak plasma concentrations are achieved immediately after IV bolus. |
| Duration of Action | Duration of action depends on dose and route. For low-dose weekly therapy (rheumatoid arthritis), clinical effects persist for about 1 week. For high-dose methotrexate (cancer), antineoplastic effects last 2-4 weeks with leucovorin rescue. Accumulation can lead to prolonged toxicity. |
| Molecular Weight | 454.44 |
Methotrexate 10 mg orally once weekly; maximum 25 mg per week.
| Dosage form | SOLUTION |
| Renal impairment | CrCl 30-50 mL/min: reduce dose by 50%; CrCl <30 mL/min: contraindicated. |
| Liver impairment | Child-Pugh Class A: caution; Class B or C: contraindicated. |
| Pediatric use | Weight-based dosing: 0.5-1 mg/kg orally once weekly; maximum 25 mg per week. |
| Geriatric use | Start at lower end of dosing range (5-7.5 mg/week) with careful monitoring for toxicity. |
| 1st trimester | Avoid; folate antagonist. Associated with neural tube defects, cardiac malformations, and cleft palate. |
| 2nd trimester | Avoid; folate antagonist. Risk of intrauterine growth restriction, hydrocephalus, and neonatal pancytopenia. |
| 3rd trimester | Avoid; folate antagonist. Risk of neonatal myelosuppression, folate deficiency, and developmental delay. |
Clinical note
Comprehensive clinical and safety monograph for XATMEP (XATMEP).
| Placental transfer | Crosses placenta; demonstrated in human studies. Active transport via folate receptors. |
| Breastfeeding | Excreted into breast milk in low concentrations but may accumulate in the infant. Not recommended due to potential for myelosuppression and folate antagonism. Use only if benefit outweighs risk. |
■ FDA Black Box Warning
Fatal or severe toxic reactions including myelosuppression, hepatic fibrosis/cirrhosis, renal failure, acute interstitial pneumonitis, and severe dermatologic reactions have been reported. Methotrexate elimination is reduced in patients with renal impairment, ascites, or pleural effusions. Use only in life-threatening neoplastic diseases, or in patients with severe, recalcitrant, disabling psoriasis or rheumatoid arthritis not responsive to other therapy. Methotrexate can cause fetal death or congenital anomalies when administered to a pregnant woman.
| Serious Effects |
PregnancyBreastfeedingPre-existing folate deficiencySevere hepatic impairmentSevere renal impairment (CrCl < 10 mL/min)Hypersensitivity to methotrexate or any component
| Precautions | Hepatotoxicity: monitor liver function tests; avoid in hepatic disease, Pulmonary toxicity: acute interstitial pneumonitis; monitor for cough/fever, Myelosuppression: monitor blood counts, Renal toxicity: reduce dose in renal impairment, Dermatologic reactions: exfoliative dermatitis, Gastrointestinal toxicity: stomatitis, diarrhea, Immunosuppression: increased risk of infection, Carcinogenicity: lymphoma risk, Concomitant NSAIDs increase toxicity, Pregnancy: contraindicated; use contraception |
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| Lactation Rating |
| L4 - Possibly Hazardous |
| Teratogenic Risk | XATMEP (methotrexate) is contraindicated in pregnancy. It is an FDA Pregnancy Category X drug. First trimester exposure causes 30-40% incidence of congenital malformations (CNS, skeletal, cardiac). Second and third trimester exposure risks fetal growth restriction, renal failure, and fetal demise. Folinic acid rescue does not eliminate risk. |
| Fetal Monitoring | In cases of inadvertent exposure: serial ultrasound for fetal anatomy and growth, fetal echocardiography at 18-22 weeks, and postnatal assessment for neurodevelopmental effects. Maternal monitoring includes CBC, LFTs, creatinine, and urinalysis at baseline and monthly during pregnancy. Folinic acid supplementation should be considered. |
| Fertility Effects | Methotrexate can cause reversible oligospermia and amenorrhea. In women, it may interfere with ovulation and implantation. Preconception counseling is recommended; men should discontinue therapy at least 3 months prior to conception to allow spermatogenesis recovery. |
| Food/Dietary |
| Avoid alcohol due to increased hepatotoxicity risk. Methotrexate absorption is not significantly affected by food, but taking with food may reduce gastrointestinal upset. Avoid excessive intake of caffeine and other xanthines. |
| Clinical Pearls | XATMEP is a methotrexate formulation designed for subcutaneous administration. It is indicated for severe psoriasis and rheumatoid arthritis. Due to its preservative-free formulation, do not use if solution is discolored or contains particulates. Administer subcutaneously, rotating injection sites. Monitor for hepatotoxicity, myelosuppression, and pulmonary fibrosis. Avoid concomitant NSAIDs to reduce toxicity risk. |
| Patient Advice | Do not share your medication with others. · Use exactly as prescribed; do not change dose or frequency without consulting your doctor. · Report any signs of infection, unusual bleeding, or shortness of breath immediately. · Avoid alcohol completely during treatment. · Do not take folic acid supplements unless directed by your doctor, as they may reduce efficacy. |