Merex

Uses

Neoplastic Diseases: Merex is used for the treatment of gestational choriocarcinoma, chorioadenoma destruens and hydatidiform mole. Merex is used in maintenance therapy in combination with other chemotherapeutic agents. Merex is used alone or in combination with other anticancer agents in the treatment of breast cancer, epidermoid cancers of the head and neck, advanced mycosis fungoides (cutaneous T cell lymphoma), and lung cancer, particularly squamous cell and small cell types. Merex is also used in combination with other chemotherapeutic agents in the treatment of advanced stage non-Hodgkin's lymphomas.

Psoriasis: Merex is used for the symptomatic control of severe, recalcitrant, disabling psoriasis that is not adequately responsive to other forms of therapy, but only when the diagnosis has been established, as by biopsy and/or after dermatologic consultation. It is important to ensure that a psoriasis “flare” is not due to an undiagnosed concomitant disease affecting immune responses.

Rheumatoid Arthritis Including Polyarticular-Course Juvenile Rheumatoid Arthritis: Merex is used for the management of selected adults with severe, active, rheumatoid arthritis (ACR criteria), or children with active polyarticular course juvenile rheumatoid arthritis, who have had an insufficient therapeutic response to, or are intolerant of, an adequate trial of first-line therapy including full dose non-steroidal anti-inflammatory agents (NSAIDs).

Aspirin, NSAIDs, and/or low dose steroids may be continued, although the possibility of increased toxicity with concomitant use of NSAIDs including salicylates has not been fully explored. Steroids may be reduced gradually in patients who respond to methotrexate. Combined use of methotrexate with gold, penicillamine, hydroxychloroquine, sulfasalazine, or cytotoxic agents, has not been studied and may increase the incidence of adverse effects. Rest and physiotherapy as used should be continued.

Merex is also used to associated treatment for these conditions: Acute Lymphocytic Leukemia (ALL), Acute Promyelocytic Leukemia (APL), Breast Cancer, Cancer, Bladder, Central Nervous System Lymphoma, Choriocarcinoma, Crohn's Disease (CD), Dermatomyositis, Disseminated Sclerosis, Extrauterine Pregnancy, Graft Versus Host Disease (GVHD), Head and Neck Carcinoma, Hydatidiform Mole, Meningeal leukemia, Polymyositis, Sarcoma, Osteogenic, Small Cell Lung Cancer (SCLC), Soft Tissue Sarcoma (STS), Squamous Cell Carcinoma of Lung, Systemic Lupus Erythematosus (SLE), Uveitis, Active Pauciarticular juvenile rheumatoid arthritis, Advanced Alibert-Bazin syndrome, Advanced non-Hodgkin lymphoma, Nonleukemic meningeal cancer, Refractory Takayasu arteritis, Severe Psoriasis, Severe, active Rheumatoid arthritis, Medically induced abortion

How Merex works

Merex enters tissues and is converted to a methotrexate polyglutamate by folylpolyglutamate.

Merex's mechanism of action is due to its inhibition of enzymes responsible for nucleotide synthesis including dihydrofolate reductase, thymidylate synthase, aminoimidazole caboxamide ribonucleotide transformylase (AICART), and amido phosphoribosyltransferase. Inhibtion of nucleotide synthesis prevents cell division.

In rheumatoid arthritis, methotrexate polyglutamates inhibit AICART more than methotrexate. This inhibition leads to accumulation of AICART ribonucleotide, which inhibits adenosine deaminase, leading to an accumulation of adenosine triphosphate and adenosine in the extracellular space, stimulating adenosine receptors, leading to anti-inflammatory action.

Dosage

Merex dosage

Oral-

• Choriocarcinoma: 15-30 mg daily for 5 days, repeat after an interval of ≥1 wk for 3-5 courses.
• Acute lymphoblastic leukaemia: Maintenance: 15 mg/m2 once or twice wkly, with other agents.
• Burkitt's lymphoma: 10-25 mg daily for 4-8 days, repeated after 7-10 days.
• Psoriasis: 10-25 mg wkly as a single dose, adjust subsequent doses based on response.
• Rheumatoid arthritis: 7.5 mg once wkly, adjust by response. Not more than 20 mg/wk.
• Mycosis fungoides: 2.5-10 mg daily to induce remission.
• Crohn's disease: 12.5-22.5 mg once wkly for up to 1 yr.

Parenteral-

• Psoriasis: 10-25 mg wkly as a single dose. Adjust subsequent doses based on response. May be given via IV/IM admin.

Intramuscular-

• Choriocarcinoma: 15-30 mg daily for 5 days. Repeat after at least 1 wk for 3-5 courses. Alternatively, 0.25-1 mg/kg (max: 60 mg) every 48 hr for 4 doses followed by folinic acid rescue, repeat at intervals of 7 days for 4 or more courses.
• Mycosis fungoides: 50 mg wkly as a single dose or 2 divided doses.
• Acute lymphoblastic leukaemia: Maintenance: 15 mg/m2 once or twice wkly, with other agents.
• Crohn's disease: 25 mg once wkly for 16 wk. Maintenance: 15 mg wkly.

Intrathecal-

• Meningeal leukaemia: 12 mg/m2 (max 15 mg) once wkly for 2-3 wk, then once mthly. Alternatively, 200-500 mcg/kg every 2-5 day until CSF cell count is normalised.

Intravenous-

• Osteosarcoma: Initial recommended dose: 12 g/m2 as a 4-hr infusion, followed by folinic acid, as part of combined therapy. May increase dose to 15 g/m2 in subsequent treatments if initial dosage is insufficient to achieve peak serum methotrexate levels of 454 mcg/mL at the end of the infusion. Merex infusion is administered on postoperative wk 4, 5, 6, 7, 11, 12, 15, 16, 29, 30, 44 and 45; in combination with other chemotherapy agents. Folinic acid can be given orally, IM or IV inj starting 24 hr after the beginning of the methotrexate infusion. Give via parenteral routes If patient experiences GI toxicity (e.g., nausea, vomiting). Usual dosage of folinic acid: 15 mg every 6 hr for a total of 60 hr or a total of 10 doses.
• Breast cancer: 10-60 mg/m2 often with cyclophosphamide and fluorouracil.
• Advanced lymphosarcoma: Up to 30 mg/kg, followed by folinic acid rescue.
• Acute lymphoblastic leukaemia: Maintenance: 2.5 mg/kg every 14 days.

Should be taken on an empty stomach. Best taken on an empty stomach. May be taken with meals to reduce GI discomfort. Avoid taking with milk-rich products.

Intramuscular: Dilute powder with D5W or normal saline to a concentration ≤25 mg/ml (20 mg and 50 mg vials) and 50 mg/ml (1 g vial).

Intrathecal: Reconstitute to 2.5-5 mg/ml with normal saline, D5W, lactated Ringer's, or Elliott's B solution. Use preservative-free preparations.

Intravenous: Dilute powder with D5W or normal saline to a concentration ≤25 mg/ml (20 mg and 50 mg vials) and 50 mg/ml (1 g vial).

Parenteral: Dilute powder with D5W or normal saline to a concentration ≤25 mg/ml (20 mg and 50 mg vials) and 50 mg/ml (1 g vial).

Side Effects

Ulceration of the mouth and GI disturbances (e.g. stomatitis and diarrhoea), bone marrow depression, hepatotoxicity, renal failure, skin reactions, alopecia, ocular irritation, arachnoiditis in intrathecal use, megaloblastic anaemia, osteoporosis, precipitation of diabetes, arthralgias, necrosis of soft tissue and bone, anaphylaxis, impaired fertility.

Toxicity

The oral LD₅₀ in rats is 135mg/kg and in mice is 146mg/kg.

Symptoms of overdose include hematologic and gastrointestinal reactions like leukopenia, thombocytopenia, anemia, pancytopenia, bone marrow suppression, mucositis, stomatitis, oral ulceration, nausea, vomiting, gastrointestinal ulceration, and gastrointestinal bleeding. In the event of an overdose, patients should be treated with glucarpidase and not be given leucovorin for 2 hours before or after glucarpidase.

Precaution

Hepatic or renal impairment, bone marrow depression, elderly, neonates. Ulcerative disorders of the GI tract. Monitor haematological, renal and hepatic function, and GI toxicity regularly.

Interaction

Decreased effectiveness with folic acid and its derivatives.

Food Interaction

• Avoid alcohol.
• Avoid milk and dairy products. Milk and dairy products reduce absorption.
• Exercise caution with St. John's Wort.
• Limit caffeine intake. Caffeine may reduce the effectiveness of methotrexate.
• Take with or without food.

[Moderate] MONITOR: Limited data suggest that consumption of greater than 180 mg

The exact mechanism of interaction is unknown but may be related to the antagonistic effect of caffeine on adenosine receptors, as anti-inflammatory properties of MTX is thought to result from the accumulation of adenosine.

In a study of 39 patients treated with MTX 7.5 mg

There were no significant differences between the responses of patients with moderate caffeine intake (120 to 180 mg

In an interview of 91 patients treated with MTX, 26% of patients who discontinued the drug were regular coffee drinkers compared to only 2% of those still receiving the drug.

Because treatment failure was the reason for MTX discontinuation in 80% of patients who discontinued, the investigators suggested that caffeine may have interfered with MTX efficacy.

MANAGEMENT: Until further information is available, the potential for interaction should be considered in patients who consume substantial amounts of caffeine and caffeine-containing foods and are prescribed methotrexate for rheumatoid arthritis.

It may be appropriate to limit caffeine intake if an interaction is suspected in cases of treatment failure.

Merex Alcohol interaction

[Moderate]

Coadministration of methotrexate with other agents known to induce hepatotoxicity may potentiate the risk of liver injury.

Merex, especially at higher doses or with prolonged treatment, has been associated with hepatotoxicity including acute hepatitis, chronic fibrosis, necrosis, cirrhosis, and liver enzyme elevations.

The risk of hepatic injury should be considered when methotrexate is used with other potentially hepatotoxic agents (e.g., acetaminophen; alcohol; androgens and anabolic steroids; antituberculous agents; azole antifungal agents; ACE inhibitors; cyclosporine (high dosages); disulfiram; endothelin receptor antagonists; interferons; ketolide and macrolide antibiotics; kinase inhibitors; minocycline; nonsteroidal anti-inflammatory agents; nucleoside reverse transcriptase inhibitors; proteasome inhibitors; retinoids; sulfonamides; tamoxifen; thiazolidinediones; tolvaptan; vincristine; zileuton; anticonvulsants such as carbamazepine, hydantoins, felbamate, and valproic acid; lipid-lowering medications such as fenofibrate, lomitapide, mipomersen, niacin, and statins; herbals and nutritional supplements such as black cohosh, chaparral, comfrey, DHEA, kava, pennyroyal oil, and red yeast rice).

Baseline and periodic monitoring of hepatic function is recommended, while liver biopsy may be warranted during long-term use of methotrexate.

Patients should be advised to seek medical attention if they experience potential signs and symptoms of hepatotoxicity such as fever, rash, itching, anorexia, nausea, vomiting, fatigue, right upper quadrant pain, dark urine, pale stools, and jaundice.

Merex Drug Interaction

Major: etanercept, adalimumab, esomeprazoleModerate: celecoxib, duloxetine, acetaminophen / hydrocodone, acetaminophenMinor: hydroxychloroquineUnknown: diphenhydramine, omega-3 polyunsaturated fatty acids, cyclobenzaprine, pregabalin, montelukast, levothyroxine, cyanocobalamin, ascorbic acid, ergocalciferol, cholecalciferol, alprazolam, cetirizine

Merex Disease Interaction

Major: infections, liver disease, myelosuppression, renal dysfunction, stomatitis

Volume of Distribution

The volume of distribution of methotrexate at steady state is approximately 1L/kg.

Elimination Route

Merex has a bioavailability of 64-90%, though this decreases at oral doses above 25mg due to saturation of the carrier mediated transport of methotrexate.. Merex has a T_max of 1 to 2 hours. oral doses of 10-15µg reach serum levels of 0.01-0.1µM.

Half Life

The half life of low dose methotrexate is 3 to 10 hours in adults. The half life for high dose methotrexate is 8 to 15 hours. Pediatric patients taking methotrexate for acute lymphoblastic anemia experience a terminal half life of 0.7 to 5.8 hours. Pediatric patients taking methotrexate for juvenile idiopathic arthritis experience a half life of 0.9 to 2.3 hours.

Clearance

Merex clearance varies widely between patients and decreases with increasing doses. Currently, predicting clearance of methotrexate is difficult and exceedingly high serum levels of methotrexate can still occur when all precautions are taken.

Elimination Route

Merex is >80% excreted as the unchanged drug and approximately 3% as the 7-hydroxylated metabolite. Merex is primarily excreted in the urine with 8.7-26% of an intravenous dose appearing in the bile.

Pregnancy & Breastfeeding use

Pregnancy category X. Studies in animals or human beings have demonstrated fetal abnormalities or there is evidence of fetal risk based on human experience or both, and the risk of the use of the drug in pregnant women clearly outweighs any possible benefit. The drug is contraindicated in women who are or may become pregnant.

Contraindication

Severe renal or hepatic impairment, pre-existing profound bone marrow suppression in patients with psoriasis or rheumatoid arthritis, alcoholic liver disease, AIDS, pre-existing blood dyscrasias, pregnancy (in patients with psoriasis or rheumatoid arthritis), breast-feeding.

Acute Overdose

Nausea, vomiting, alopecia, melena, and renal failure.

Storage Condition

Store at room temperature (15-25°C).

Innovators Monograph

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