methotrexate 7.5 MG Oral Tablet [Trexall]

INDICATIONS AND USAGE Methotrexate for Injection is a folate analog metabolic inhibitor indicated for: • The following neoplastic diseases for the: ○ Treatment of adult and pediatric patients with acute lymphoblastic leukemia as part of a combination chemotherapy regimen (1.1) ○ Prophylaxis and treatment of adult and pediatric patients with meningeal leukemia (1.2) ○ Treatment of adult and pediatric patients with non-Hodgkin lymphoma (1.3) ○ Treatment of adult and pediatric patients with osteosarcoma as part of a combination chemotherapy regimen (1.4) ○ Treatment of adults with breast cancer as part of a combination chemotherapy regimen (1.5) ○ Treatment of adults with squamous cell carcinoma of the head and neck as single-agent (1.6) ○ Treatment of adults with gestational trophoblastic neoplasia as part of a combination chemotherapy regimen (1.7) • Treatment of adults with rheumatoid arthritis (RA). (1.8) • Treatment of pediatric patients with polyarticular juvenile idiopathic arthritis (pJIA). (1.9) • Treatment of adults with severe psoriasis. (1.10) 1.1 Acute Lymphoblastic Leukemia Methotrexate for Injection is indicated for the treatment of adult and pediatric patients with acute lymphoblastic leukemia (ALL) as part of a combination chemotherapy regimen. 1.2 Meningeal Leukemia: Prophylaxis and Treatment Methotrexate for Injection is indicated for the prophylaxis and treatment of meningeal leukemia in adult and pediatric patients. 1.3 Non-Hodgkin Lymphoma Methotrexate for Injection is indicated for the treatment of adults and pediatric patients with Non-Hodgkin lymphoma. 1.4 Osteosarcoma Methotrexate for Injection is indicated for the treatment of adults and pediatric patients with osteosarcoma as part of a combination chemotherapy regimen. 1.5 Breast Cancer Methotrexate for Injection is indicated for the treatment of adults with breast cancer as part of a combination chemotherapy regimen. 1.6 Squamous Cell Carcinoma of the Head and Neck Methotrexate for Injection is indicated for the treatment of adults with squamous cell carcinoma of the head and neck as a single-agent. 1.7 Gestational Trophoblastic Neoplasia Methotrexate for Injection is indicated for the treatment of adults with gestational trophoblastic neoplasia (GTN) as part of a combination chemotherapy regimen. 1.8 Rheumatoid Arthritis Methotrexate for Injection is indicated for the treatment of adults with rheumatoid arthritis (RA). 1.9 Polyarticular Juvenile Idiopathic Arthritis Methotrexate for Injection is indicated for the treatment of pediatric patients with polyarticular Juvenile Idiopathic Arthritis (pJIA). 1.10 Psoriasis Methotrexate for Injection is indicated for the treatment of adults with severe psoriasis.

DOSAGE AND ADMINISTRATION • Verify pregnancy status in females of reproductive potential before starting Methotrexate Injection. ( 2.1 , 4 , 5.1 ) • Neoplastic diseases: Refer to the prescribing information for disease specific dosing recommendations. Follow guidelines for high-dose regimens. ( 2.2 , 2.3 , 2.4 , 2.5 , 2.6 , 2.7 , 2.8 , 2.9 ) • RA: Recommended starting dosage of 7.5 mg once weekly intramuscularly; adjust dose to achieve an optimal response. ( 2.10 ) • pJIA: Recommended starting dosage of 10 mg/m 2 once weekly subcutaneously or intramuscularly; adjust dose to achieve an optimal response. ( 2.11 ) • Psoriasis: Recommended dosage of 10 mg to 25 mg once weekly intramuscularly or intravenously; adjust dose to achieve optimal response. Once achieved, reduce to lowest possible dosage. ( 2.12 ) 2.1 Important Dosage and Safety Information • Use only preservative-free Methotrexate Injection for treatment of neonates or low birth weight infants and for intrathecal use. Do not use benzyl alcohol-containing formulations for high-dose regimens unless immediate treatment is required and preservative-free formulations are not available [see Warnings and Precautions (5.3) and Use in Specific Populations (8.4) ]. • Verify pregnancy status in females of reproductive potential before starting Methotrexate Injection [see Contraindications (4) and Warnings and Precautions (5.1) ]. • For patients switching between a methotrexate product administered orally and Methotrexate Injection, consider potential differences in bioavailability . 2.2 Recommended Monitoring and Concomitant Therapies for Intermediate- and High-Dose Regimens To decrease the risk of severe adverse reactions [see Warnings and Precautions (5) ] : • Administer leucovorin rescue in patients receiving Methotrexate Injection doses of 500 mg/m 2 or greater (e.g., high-dose) . • Consider leucovorin rescue for patients receiving Methotrexate Injection doses between 100 mg/m 2 to less than 500 mg/m 2 (e.g., intermediate-dose). Refer to the leucovorin prescribing information for additional information. • For high-dose Methotrexate Injection regimens, follow the supportive care and monitoring instructions below. Also consider for patients receiving intermediate-dose Methotrexate Injection regimens. - Monitor serum creatinine, electrolytes, at baseline and at least daily during therapy - Administer intravenous fluids starting before the first dose and continuing throughout treatment to maintain adequate hydration and urine output - Alkalinize urine starting before the first dose and continuing throughout treatment to maintain a urinary pH of 7 or higher - Monitor methotrexate concentrations at least daily and adjust hydration and leucovorin dosing as needed • Administer glucarpidase in patients who have toxic plasma methotrexate concentrations (>1 micromole per liter) and delayed methotrexate clearance due to impaired renal function (refer to the glucarpidase prescribing information for additional information). 2.3 Recommended Dosage for Acute Lymphoblastic Leukemia Methotrexate Injection is used as part of a multi-drug regimen. The recommended dosage varies from 10 to 5000 mg/m 2 intravenously. For high-dose Methotrexate Injection regimens, use leucovorin rescue in accordance with high-dose methotrexate regimen guidelines [see Dosage and Administration (2.2) ] . Lower doses (e.g., 20 to 30 mg/m 2 per week) may be used intramuscularly. Individualize the dose and schedule of Methotrexate Injection based on disease state, patient risk category, concurrent drugs used, phase of treatment, and response to treatment. 2.4 Recommended Dosage for Meningeal Leukemia: Prophylaxis and Treatment Use only preservative-free Methotrexate Injection for intrathecal use. Prior to administration, dilute preservative-free Methotrexate Injection to a concentration of 1 mg/mL in preservative-free 0.9% Sodium Chloride Injection, USP. The recommended intrathecal dose of Methotrexate Injection (preservative-free) is based on age: • less than 1 year: 6 mg • 1 to less than 2 years: 8 mg • 2 to less than 3 years: 10 mg • 3 to less than 9 years: 12 mg • greater than or equal to 9 years: 12 to15 mg For treatment of meningeal leukemia, intrathecal methotrexate may be given at intervals of 2 or more days up to twice weekly; however, administration at intervals of less than 1 week may result in increased subacute toxicity. For meningeal leukemia prophylaxis, Methotrexate Injection is administered no more than once weekly. For patients with Down Syndrome, administer leucovorin rescue with intrathecal Methotrexate Injection. 2.5 Recommended Dosage for Non-Hodgkin Lymphoma The recommended dosage of Methotrexate Injection varies. When used in combination, recommended dosages range from 10 mg/m 2 to 8000 mg/m 2 intravenously. When used as a single agent, recommended dosages include 8000 mg/m 2 intravenously for central nervous system-directed therapy or 5 to 75 mg intravenously for cutaneous forms of non-Hodgkin lymphoma. As part of a combination chemotherapy regimen, a recommended dosage of Methotrexate Injection is 1000 mg/m 2 or 3000 mg/m 2 as an intravenous infusion over 24 hours followed by leucovorin rescue in accordance with high-dose methotrexate regimen guidelines [see Dosage and Administration (2.2) ] . For central nervous system-directed therapy, a recommended dosage of Methotrexate Injection is 8000 mg/m 2 as an intravenous infusion over 4 hours as a single agent or in combination with immunochemotherapy at doses ranging from 3000 mg/m 2 to 8000 mg/m 2 followed by leucovorin rescue in accordance with high-dose methotrexate regimen guidelines [see Dosage and Administration (2.2) ] . For intrathecal Methotrexate Injection (preservative-free), the recommended dose is based on age [see Dosage and Administration (2.4) ] . The frequency of administration varies based on whether it is being used for treatment or prophylaxis, and other factors. 2.6 Recommended Dosage for Osteosarcoma The recommended dosage of Methotrexate Injection is typically 12 g/m 2 (maximum 20 g/dose) as an intravenous infusion over 4 hours administered as a component of a combination chemotherapy regimen. Administer leucovorin rescue in accordance with high-dose methotrexate regimen guidelines [see Dosage and Administration (2.2) ]. Subsequent doses may need to be adjusted based on observed peak serum methotrexate concentrations. Dosage and schedule may vary based upon factors such as patient comorbidities, disease state, and prior treatments. 2.7 Recommended Dosage for Breast Cancer A recommended dosage of Methotrexate Injection is 40 mg/m 2 intravenously as a component of a cyclophosphamide- and fluorouracil-based multi-drug regimen. 2.8 Recommended Dosage for Squamous Cell Carcinoma of Head and Neck The recommended dosage of Methotrexate Injection ranges from 40 to 60 mg/m 2 intravenously once weekly. 2.9 Recommended Dosage for Gestational Trophoblastic Neoplasia For patients with low-risk gestational trophoblastic neoplasia (GTN) a recommended dosage for Methotrexate Injection is 30 mg/m 2 to 200 mg/m 2 or 0.4 mg/kg to1 mg/kg intravenously or intramuscularly. For patients with high-risk GTN, a recommended dosage for Methotrexate Injection is 300 mg/m 2 over 12 hours as an intravenous infusion as a component of a multi-drug regimen. 2.10 Recommended Dosage for Rheumatoid Arthritis The recommended starting dosage of Methotrexate Injection is 7.5 mg once weekly, administered intramuscularly with escalation to achieve optimal response. Dosages of more than 20 mg once weekly result in an increased risk of serious adverse reactions, including myelosuppression. When responses are observed, the majority occurred between 3 and 6 weeks from initiation of treatment; however, responses have occurred up to 12 weeks after treatment initiation. Administer folic acid or folinic acid to reduce the risk of methotrexate adverse reactions [see Warnings and Precautions (5.12) ].

WARNINGS AND PRECAUTIONS • Serious Infections : Monitor patients for infection during and after treatment with methotrexate. Withhold or discontinue methotrexate for serious infections as appropriate. (5.11) • Neurotoxicity : Monitor patients for neurotoxicity and withhold or discontinue methotrexate as appropriate. (5.12) • Secondary Malignancies : Can occur with methotrexate. (5.13) • Tumor Lysis Syndrome : Institute appropriate prophylactic measures in patients at risk for tumor lysis syndrome prior to initiation of methotrexate (5.14) • Immunizations and Risk Live Vaccines : Immunizations with live vaccines is not recommended. Follow current vaccination practice guidelines. (5.15) • Infertility : Can cause impairment of fertility, oligospermia, and menstrual dysfunction. (5.16, 8.3) 5.1 Embryo-Fetal Toxicity Based on published reports and its mechanism of action, methotrexate can cause fetal harm, including fetal death, when administered to a pregnant woman. Methotrexate is contraindicated for use in pregnant women receiving methotrexate for the treatment of non-malignant diseases. Advise pregnant women with neoplastic diseases of the potential risk to a fetus. Advise females of reproductive potential to use effective contraception during treatment with methotrexate and for 6 months after the final dose. Advise males with female partners of reproductive potential to use effective contraception during methotrexate treatment and for 3 months after the final dose [see Contraindications (4), Use in Specific Populations (8.1, 8.3)]. 5.2 Hypersensitivity Reactions Hypersensitivity reactions, including anaphylaxis, can occur with methotrexate [see Contraindications (4), Adverse Reactions (6.1)]. If anaphylaxis or other serious hypersensitivity reaction occurs, immediately and permanently discontinue methotrexate [see Dosage and Administration (2.6)]. 5.3 Myelosuppression Methotrexate suppresses hematopoiesis and can cause severe and life-threatening pancytopenia, anemia, leukopenia, neutropenia, and thrombocytopenia [see Adverse Reactions (6.1)]. Obtain blood counts at baseline, periodically during treatment, and as clinically indicated. Monitor patients for clinical complications of myelosuppression. Withhold, dose reduce, or discontinue methotrexate taking into account the importance of methotrexate tablet treatment in the context of the severity of the disease being treated, the severity of the adverse drug reaction, and availability of alternative therapy [see Dosage and Administration (2.6)]. 5.4 Gastrointestinal Toxicity Diarrhea, vomiting, nausea, and stomatitis occurred in up to 10% of patients receiving methotrexate for treatment of non-neoplastic diseases. Hemorrhagic enteritis and fatal intestinal perforation have been reported [see Adverse Reactions (6.1, 6.2)]. Patients with peptic ulcer disease or ulcerative colitis are at a greater risk of developing severe gastrointestinal adverse reactions [see Drug Interactions (7.1)]. Withhold or discontinue methotrexate for severe gastrointestinal toxicity taking into account the importance of methotrexate tablet treatment in the context of the severity of the disease being treated, the severity of the adverse drug reaction, and availability of alternative therapy [see Dosage and Administration (2.6)]. 5.5 Hepatotoxicity Methotrexate can cause severe and potentially irreversible hepatotoxicity, including fibrosis, cirrhosis, and fatal liver failure [see Adverse Reactions (6.1)]. The safety of methotrexate in patients with hepatic disease is unknown. The risk of hepatotoxicity is increased with heavy alcohol consumption. In patients with psoriasis, fibrosis or cirrhosis may occur in the absence of symptoms or abnormal liver tests; the risk of hepatotoxicity appears to increase with total cumulative dose and generally occurs after receipt of a total cumulative dose of 1.5 g or more. Monitor liver tests at baseline, periodically during treatment and as clinically indicated. Withhold or discontinue methotrexate taking into account the importance of methotrexate tablet treatment in the context of the severity of the disease being treated, the severity of the adverse drug reaction, and availability of alternative therapy [see Dosage and Administration (2.6)]. 5.6 Pulmonary Toxicity Pulmonary toxicity, including acute or chronic interstitial pneumonitis and irreversible or fatal cases, can occur with methotrexate [see Adverse Reactions (6.1, 6.2)]. Monitor patients for pulmonary toxicity and withhold or discontinue methotrexate taking into account the importance of methotrexate tablet treatment in the context of the severity of the disease being treated, the severity of the adverse drug reaction, and availability of alternative therapy [see Dosage and Administration (2.6)]. 5.7 Dermatologic Reactions Severe, including fatal dermatologic reactions, such as toxic epidermal necrolysis, Stevens-Johnson syndrome, exfoliative dermatitis, skin necrosis, and erythema multiforme, can occur with methotrexate [see Adverse Reactions (6.1, 6.2)]. Exposure to ultraviolet radiation while taking methotrexate may aggravate psoriasis. Methotrexate can cause radiation recall dermatitis and photodermatitis (sunburn) reactivation. Monitor patients for dermatologic toxicity and withhold or permanently discontinue methotrexate for severe dermatologic reactions taking into account the importance of methotrexate tablet treatment in the context of the severity of the disease being treated, the severity of the adverse drug reaction, and availability of alternative therapy [see Dosage and Administration (2.6)]. Advise patients to avoid excessive sun exposure and use sun protection measures. 5.8 Renal Toxicity Methotrexate can cause renal toxicity, including irreversible acute renal failure [see Adverse Reactions (6.2)]. Monitor renal function at baseline, periodically during treatment and as clinically indicated. Withhold or discontinue methotrexate for severe renal toxicity taking into account the importance of methotrexate tablet treatment in the context of the severity of the disease being treated, the severity of the adverse drug reaction, and availability of alternative therapy [see Dosage and Administration (2.6)]. Administer glucarpidase in patients with toxic plasma methotrexate concentrations (> 1 micromole per liter) and delayed methotrexate clearance due to impaired renal function. Refer to the glucarpidase prescribing information for additional information. 5.9 Risk of Serious Adverse Reactions with Medication Error Deaths occurred in patients as a result of medication errors. Most commonly, these errors occurred in patients who were taking methotrexate daily when a weekly dosing regimen was prescribed. For patients prescribed a once weekly dosing regimen, instruct patients and caregivers to take the recommended dosage as directed, because medication errors have led to death. 5.10 Folic Acid Supplementation Neoplastic Diseases Products containing folic acid or its derivatives may decrease the clinical effectiveness of methotrexate. Therefore, instruct patients not to take products containing folic acid or folinic acid unless directed to do so by their healthcare provider. Non-neoplastic Diseases Folate deficiency may increase methotrexate adverse reactions. Administer folic acid or folinic acid for patients with rheumatoid arthritis, pJIA, and psoriasis [see Dosage and Administration (2.3, 2.4, 2.5)]. 5.11 Serious Infections Patients treated with methotrexate are at increased risk for developing life-threatening or fatal bacterial, fungal, or viral infections, including opportunistic infections such as Pneumocystis jiroveci pneumonia, invasive fungal infections, hepatitis B reactivation, tuberculosis primary infection or reactivation, and disseminated Herpes zoster and cytomegalovirus infections [see Adverse Reactions (6.2)]. Monitor patients for infection during and after treatment with methotrexate. Withhold or discont

CONTRAINDICATIONS Methotrexate can cause fetal death or teratogenic effects when administered to a pregnant woman. Methotrexate is contraindicated in pregnant women with psoriasis or rheumatoid arthritis and should be used in the treatment of neoplastic diseases only when the potential benefit outweighs the risk to the fetus. Women of childbearing potential should not be started on methotrexate until pregnancy is excluded and should be fully counseled on the serious risk to the fetus (see PRECAUTIONS ) should they become pregnant while undergoing treatment. Pregnancy should be avoided if either partner is receiving methotrexate; during and for a minimum of three months after therapy for male patients, and during and for at least one ovulatory cycle after therapy for female patients. (see Boxed WARNINGS ). Because of the potential for serious adverse reactions from methotrexate in breast fed infants, it is contraindicated in nursing mothers. Patients with psoriasis or rheumatoid arthritis with alcoholism, alcoholic liver disease or other chronic liver disease should not receive methotrexate. Patients with psoriasis or rheumatoid arthritis who have overt or laboratory evidence of immunodeficiency syndromes should not receive methotrexate. Patients with psoriasis or rheumatoid arthritis who have preexisting blood dyscrasias, such as bone marrow hypoplasia, leukopenia, thrombocytopenia, or significant anemia, should not receive methotrexate. Patients with a known hypersensitivity to methotrexate should not receive the drug.

CLINICAL PHARMACOLOGY Methotrexate inhibits dihydrofolic acid reductase. Dihydrofolates must be reduced to tetrahydrofolates by this enzyme before they can be utilized as carriers of one- carbon groups in the synthesis of purine nucleotides and thymidylate. Therefore, methotrexate interferes with DNA synthesis, repair, and cellular replication. Actively proliferating tissues such as malignant cells, bone marrow, fetal cells, buccal and intestinal mucosa, and cells of the urinary bladder are in general more sensitive to this effect of methotrexate. When cellular proliferation in malignant tissues is greater than in most normal tissues, methotrexate may impair malignant growth without irreversible damage to normal tissues. The mechanism of action in rheumatoid arthritis is unknown; it may affect immune function. Two reports describe in vitro methotrexate inhibition of DNA precursor uptake by stimulated mononuclear cells, and another describes in animal polyarthritis partial correction by methotrexate of spleen cell hyporesponsiveness and suppressed IL 2 production. Other laboratories, however, have been unable to demonstrate similar effects. Clarification of methotrexate’s effect on immune activity and its relation to rheumatoid immunopathogenesis await further studies. In patients with rheumatoid arthritis, effects of methotrexate on articular swelling and tenderness can be seen as early as 3 to 6 weeks. Although methotrexate clearly ameliorates symptoms of inflammation (pain, swelling, stiffness), there is no evidence that it induces remission of rheumatoid arthritis nor has a beneficial effect been demonstrated on bone erosions and other radiologic changes which result in impaired joint use, functional disability, and deformity. Most studies of methotrexate in patients with rheumatoid arthritis are relatively short term (3 to 6 months). Limited data from long-term studies indicate that an initial clinical improvement is maintained for at least two years with continued therapy. In psoriasis, the rate of production of epithelial cells in the skin is greatly increased over normal skin. This differential in proliferation rates is the basis for the use of methotrexate to control the psoriatic process. Methotrexate in high doses, followed by leucovorin rescue, is used as a part of the treatment of patients with non-metastatic osteosarcoma. The original rationale for high-dose methotrexate therapy was based on the concept of selective rescue of normal tissues by leucovorin. More recent evidence suggests that high-dose methotrexate may also overcome methotrexate resistance caused by impaired active transport, decreased affinity of dihydrofolic acid reductase for methotrexate, increased levels of dihydrofolic acid reductase resulting from gene amplification, or decreased polyglutamation of methotrexate. The actual mechanism of action is unknown. In a 6-month double-blind, placebo-controlled trial of 127 pediatric patients with juvenile rheumatoid arthritis (JRA) (mean age, 10.1 years; age range, 2.5 to 18 years; mean duration of disease, 5.1 years) on background nonsteroidal anti-inflammatory drugs (NSAIDs) and/or prednisone, methotrexate given weekly at an oral dose of 10 mg/m 2 provided significant clinical improvement compared to placebo as measured by either the physician’s global assessment, or by a patient composite (25% reduction in the articular-severity score plus improvement in parent and physician global assessments of disease activity). Over two-thirds of the patients in this trial had polyarticular-course JRA, and the numerically greatest response was seen in this subgroup treated with 10 mg/m 2 /wk methotrexate. The overwhelming majority of the remaining patients had systemic-course JRA. All patients were unresponsive to NSAIDs; approximately one-third were using low dose corticosteroids. Weekly methotrexate at a dose of 5 mg/m 2 was not significantly more effective than placebo in this trial. Two Pediatric Oncology Group studies (one randomized and one non-randomized) demonstrated a significant improvement in relapse-free survival in patients with non-metastatic osteosarcoma, when high-dose methotrexate with leucovorin rescue was used in combination with other chemotherapeutic agents following surgical resection of the primary tumor. These studies were not designed to demonstrate the specific contribution of high-dose methotrexate/leucovorin rescue therapy to the efficacy of the combination. However, a contribution can be inferred from the reports of objective responses to this therapy in patients with metastatic osteosarcoma, and from reports of extensive tumor necrosis following preoperative administration of this therapy to patients with non-metastatic osteosarcoma. Pharmacokinetics Absorption Oral absorption appears to be dose dependent. Peak plasma concentrations are reached within 0.75 to 6 hours following oral administration. At doses of 30 mg/m 2 or less, methotrexate is generally well absorbed with a mean bioavailability of about 60%. The absorption of doses greater than 80 mg/m 2 is significantly less, possibly due to a saturation effect. In leukemic pediatric patients, oral absorption of methotrexate also appears to be dose dependent and has been reported to vary widely (23% to 95%). A twenty fold difference between highest and lowest peak levels (C max : 0.11 to 2.3 micromolar after a 20 mg/m 2 dose) has been reported. Significant interindividual variability has also been noted in time to peak concentration (T max : 0.67 to 4 hrs after a 15 mg/m 2 dose) and fraction of dose absorbed. The absorption of doses greater than 40 mg/m 2 has been reported to be significantly less than that of lower doses. Food has been shown to delay absorption and reduce peak concentration. Methotrexate is generally completely absorbed from parenteral routes of injection. After intramuscular injection, peak serum concentrations occur in 30 to 60 minutes. As in leukemic pediatric patients, a wide interindividual variability in the plasma concentrations of methotrexate has been reported in pediatric patients with JRA. Following oral administration of methotrexate in doses of 6.4 to 11.2 mg/m 2 /week in pediatric patients with JRA, mean serum concentrations were 0.59 micromolar (range, 0.03 to 1.40) at 1 hour, 0.44 micromolar (range, 0.01 to 1.00) at 2 hours, and 0.29 micromolar (range, 0.06 to 0.58) at 3 hours. In pediatric patients receiving methotrexate for acute lymphocytic leukemia (6.3 to 30 mg/m 2 ), or for JRA (3.75 to 26.2 mg/m 2 ), the terminal half-life has been reported to range from 0.7 to 5.8 hours or 0.9 to 2.3 hours, respectively. Distribution -After intravenous administration, the initial volume of distribution is approximately 0.18 L/kg (18% of body weight) and steady-state volume of distribution is approximately 0.4 to 0.8 L/kg (40 to 80% of body weight). Methotrexate competes with reduced folates for active transport across cell membranes by means of a single carrier-mediated active transport process. At serum concentrations greater than 100 micromolar, passive diffusion becomes a major pathway by which effective intracellular concentrations can be achieved. Methotrexate in serum is approximately 50% protein bound. Laboratory studies demonstrate that it may be displaced from plasma albumin by various compounds including sulfonamides, salicylates, tetracyclines, chloramphenicol, and phenytoin. Methotrexate does not penetrate the blood-cerebrospinal fluid barrier in therapeutic amounts when given orally or parenterally. High CSF concentrations of the drug may be attained by intrathecal administration. In dogs, synovial fluid concentrations after oral dosing were higher in inflamed than uninflamed joints. Although salicylates did not interfere with this penetration, prior prednisone treatment reduced penetration into inflamed joints to the level of normal joints. Metabolism After absorption, methotrexate undergoes hepatic and intracellular