Overdose : מינון יתר

4.9 Overdose
Symptoms of overdose
Toxicity of methotrexate mainly affects the haematopoietic and gastrointestinal systems. Symptoms include leukocytopenia, thrombocytopenia, anaemia, pancytopenia, neutropenia, bone marrow depression, mucositis, stomatitis, oral ulceration, nausea, vomiting, gastrointestinal ulceration and gastrointestinal bleeding. Some patients showed no signs of overdose.
There are reports of death due to sepsis, septic shock, renal failure and aplastic anaemia.
Therapeutic measures in case of overdose
Calcium folinate is the specific antidote for neutralising the toxic undesirable effects of methotrexate.
In cases of accidental overdose, a dose of calcium folinate equal to or higher than the offending dose of methotrexate should be administered intravenously or intramuscularly within one hour and dosing continued until the serum levels of methotrexate are below 10–7 mol/l.
In cases of massive overdose, hydration and urinary alkalisation may be necessary to prevent precipitation of methotrexate and/or its metabolites in the renal tubules. Neither haemodialysis nor peritoneal dialysis has been shown to improve methotrexate elimination. Effective clearance of methotrexate has been reported with acute, intermittent haemodialysis using a high flux dialyser.
In patients with rheumatoid arthritis, polyarticular juvenile idiopathic arthritis, psoriasis arthritis or psoriasis vulgaris, administration of folic or folinic acid may reduce methotrexate toxicity (gastrointestinal symptoms, inflammation of oral mucosa, hair loss and increase of liver enzymes), see section 4.5. Prior to using folic acid products, monitoring of vitamin B12 levels is recommended, since folic acid may mask an existing vitamin B12 deficiency, particularly in adults over 50 years of age.