Medication Prescribing Error Reporting and Prevention Program: A 14-Year Experience

Timothy S. Lesar, PharmD

Disclosures

August 14, 2000

In This Article

METHOTREXATE

Order using Antineoplastic Order Sheet

Forms available: Tablet: 2.5mg; Injection: 20mg (preservative free), 250mg/10ml

Uses: An antimetabolite that inhibits dihydrofolate reductase and blocks conversion of folic acid to tetrahydrofolic acid. Has immunosuppressive activity. It is used to treat trophoblastic tumors, acute lymphocytic leukemia, breast, lung and head and neck cancers and a variety of other solid tumors. High dose methotrexate is used as an adjunct to surgery for nonmetastatic osteosarcoma. Also used in severe psoriasis, rheumatoid arthritis, and ectopic pregnancy.

Contraindications: Renal impairment (CrCl <40ml/min), leukopenia, thrombocytopenia, patients with presence of pleural or peritoneal effusions, pregnancy and nursing mothers. In management of psoriasis and rheumatoid arthritis, methotrexate is contraindicated in those with poor nutritional status, evidence of an immunodeficiency syndrome and preexisting blood dyscrasias, significant anemia, excessive alcohol consumption, alcoholic liver disease or chronic liver disease.

Precautions: Use with extreme caution in patients with renal impairment, infection, peptic ulcer, ulcerative colitis, or in the very young or elderly. Methotrexate levels must be monitored and leucovorin rescue used in patients receiving high dose regimens >200mg/m2. Prolonged elimination and greater potential for toxicity is present in patients with edema, ascites, effusions or ileus.

Usual Dose: Dose varies, consult published protocols.

SOLID TUMORS:
Adults: 20-40mg/m2/dose IV q1-2weeks

LEUKEMIAS AND LYMPHOMAS:
Adults: 200-500mg/m2/dose IV q2-4weeks

OSTEOSARCOMA:
Adults: 12-15g/m2/dose IV (with leucovorin rescue)

INTRATHECAL:
Adults: 12mg

PSORIASIS:
Adults: 5-10mg PO given 1 week prior to initiation to detect reactions followed by: (A) 2.5-5mg PO q12h for 3 doses weekly or q8h for 4 doses weekly. Increase dose by 2.5mg/week but do not exceed 30mg/week; OR

(B) 10-25mg PO/IM/IV once weekly. Increase dose by 2.5-5mg weekly but do not exceed 50mg/wk; OR

(C) 2.5mg PO daily for 5 days then 2 days rest. Daily dose should not exceed 6.25mg. There may be more hepatotoxicity with this regimen.

RHEUMATOID ARTHRITIS:
Children: 5-15mg/m2/week PO/IM as single dose or in 3 divided doses given 12h apart. Must take care when prescribing. Numerous serious errors have occurred when mistakenly prescribed to be given "daily" instead of intermittently (i.e. weekly).
Adults: Initially 7.5mg PO weekly as a single dose or as 2.5mg q12h for 3 doses. Increase dose gradually but do not exceed 20mg/week. Optimum response may require 3 months or more of therapy. Use of folic acid 1mg/day may reduce side effects.

ECTOPIC PREGNANCY: 50mg/m2 IM for one dose.

Common adverse effects: Myelosuppression, stomatitis, enteritis, ulcerations, nausea and vomiting (at high dose), elevated liver function tests, rash. Severe effects include hepatic fibrosis, cirrhosis, pneumonitis, pulmonary fibrosis, neurotoxicity, and nephrotoxicity.

Critical drug interactions: Drugs such as salicylates, sulfonamides, sulfonylureas, phenytoin, and tetracyclines may displace methotrexate from its binding sites and increase toxicity. Salicylates, probenecid, and NSAIDs may inhibit renal elimination of methotrexate, resulting in elevated and prolonged serum concentrations of methotrexate.

Monitoring: CBC, renal and liver function. Methotrexate level starting 24h after beginning high dose methotrexate and every 24h until level is < 0.05µM. See "AMC Guide to Serum/Blood Concentration Monitoring in Orange Section. Complete blood counts, renal function and liver function must be monitored at 1-3 month intervals throughout therapy for psoriasis or rheumatoid arthritis and more frequently for malignant diseases.

Nursing Implications: Administer antiemetics. Observe for GI toxicity. Leucovorin rescue must begin 24h after the BEGINNING of the methotrexate dose. Patients receiving high dose methotrexate must receive adequate hydration with urinary alkalinization. Refer to High dose Methotrexate protocol and Emergent Care of Patient with Unruptured Ectopic Pregnancy with Methotrexate Protocol, as appropriate. Provide chemotherapy teaching. Refer to Chemotherapy protocol and, if necessary, the AMCH Antineoplastic Handbook.

SALMETEROL (SereventR) ($45 per MDI)

Forms available: Inhaler: 21mcg per actuation.

Uses: A long acting beta-agonist bronchodilator for prevention of bronchospasm in reversible airway disease and exercise induced bronchospasm. NOT TO BE USED FOR TREATMENT OF ACUTE SYMPTOMS.

Contraindications: Hypersensitivity to components.

Precautions: Do not use for acute symptoms, do not exceed recommended dose.

Usual dose:
Adults: Two actuations twice daily. For exercise induced bronchospasm administer at least 30-60min prior to exercise. Not for "as needed" use.

Common adverse effects: Tachycardia, palpitations, tremor, headache, nervousness, bronchospasm, hypersensitivity.

Critical drug interactions: Use short-acting beta agonist bronchodilators only for symptomatic relief. Increased use of short acting agents in patients on salmeterol may represent clinical deterioration. Use caution in patients taking an MAOI.

Nursing implications: Instruct patient on correct inhaler use. Not to be used for treatment of acute symptoms or on an "as needed" basis.

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