1 - METHOTREXATE Flashcards
Methotrexate is a chemotherapeutic agent
True (cytotoxic and teratogenic)
Methotrexate is an immunosuppressive agent
True
MTX is often used with TNF-alpha antagonists
True (FDA approved in patients with arthritis)
Methotrexate is a potential competitive antagonist and inhibitor of dihydrofolate reductase
True
Methotrexate is structurally similar to folic acid
True
Folic acid is the natural substrate for the enzyme dihydropteroate synthetase and dihydrofolate reductase
True
Methotrexate can be administered orally
True
Methotrexate can be administered intravenously
True
Methotrexate can be administered intramuscularly
True
Methotrexate can be administered subcutaneously
True
Methotrexate is rapidly absorbed through the GI tract
True
Peak plasma levels of orally administered Methotrexate are reached more slowly than intravenous or subcutaneous/intramuscular route
True
The oral route of Methotrexate provides more reliable blood levels than parenteral administration even though the absorption of oral methotrexate may be incomplete and variable with doses > 15mg
True
Concurrent food intake, particularly milk-based meals may reduce bioavailability in children
True (though bioavailability in adults is not affected by concurrent food ingestion)
The bioavailability of methotrexate in adults is not affected by concurrent food ingestion
True
The absorption of methotrexate may be reduced by non-absorbable antibiotics such as neomycin
True
Methotrexate does not penetrate the blood brain barrier well
True (the reason why intrathecal methotrexate is needed in some chemotherapy regimens)
The level of plasma Methotrexate once absorbed, has a triphasic reduction
True
The first phase of the triphasic reduction of plasma methotrexate occurs rapidly over 0.75 hours and reflects distribution of the drug throughout the body
True
The second phase of the triphasic reduction of plasma methotrexate occurs over 2-4 hours and reflects renal excretion
True
The third phase of the triphasic reduction of plasma methotrexate occurs between 10 and 27 hours and reflects the terminal half life and slow release of methotrexate primarily bound to dihydrofolate reductase from the tissues
True
Methotrexate is a weak organic acid and is excreted through the kidneys
True
Methotrexate is a weak organic acid predominately excreted through the kidneys; MTX glomerular filtration and active tubular secretion are susceptible to drug interactions with other weak acids I.e. Salicylates, probenecid, and sulfonamides
True
Approx 50% of methotrexate is bound to plasma proteins and 50% is the unbound free fraction/active portion of the drug
True
The beneficial effects and potential for toxicity is increased when the unbound free fraction of methotrexate is increased by certain drugs I.e. Salicylates, sulfonamides, probenecid
True
Methotrexate is metabolised intracellularly in all cells that it is actively transported into, including the liver
True
Methotrexate is metabolised intracellularly to polyglutamated forms/metabolites which are potent inhibitors of dihydrofolate reductase and play a key role in methotrexate toxicity
True
The polyglutamated metabolites of intracellular methotrexate metabolism contributes toward methotrexate toxicity
True (the metabolites are also dihydrofolate reductase inhibitors)
Methotrexate has a greater affinity to dihydrofolate reductase than the enzyme’s natural substrate folic acid
True
Folic acid (natural substrate of dihydrofolate reductase) is converted to tetrahydrofolate by dihydrofolate reductase
True
Tetrahydrofolate is converted to DNA by thymidylate synthetase
True
Methotrexate competitively and irreversibly binds to dihydrofolate reductase with a greater affinity than folic acid
True (prevents conversion of dihydrofolate to tetrahydrofolate)
Methotrexate prevents the conversion of dihydrofolate to tetrahydrofolate by competitively and irreversibly binding to dihydrofolate reductase
True
Methotrexate also competitively and partially reversibly inhibits thymidylate synthetase within 24 hours of methotrexate administration to prevent thymidine and purine nucleotide synthesis to take place from tetrahydrofolate
True (affects DNA synthesis)
The overall effect of methotrexate is inhibition of DNA synthesis/cell division which takes place during the S phase of the cell cycle
True
The competitive and irreversible inhibition of dihydrofolate reductase by methotrexate can be bypassed by Leucovorin (folinic acid)
True (thus folinic rescue may reverse the acute haematologic toxicity secondary to methotrexate)
Leucovorin (folinic acid) may reverse the acute haematologic toxicity secondary to methotrexate
True
Methotrexate acts via an immunosuppressive mechanism by affecting the proliferation of lymphocytes
True