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Published Online, 25 April 2006, www.theannals.com, DOI 10.1345/aph.1G334.
The Annals of Pharmacotherapy: Vol. 40, No. 5, pp. 805-811. DOI 10.1345/aph.1G334
© 2006 Harvey Whitney Books Company.
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MEDICATION SAFETY

Occurrence and Impact of Unanticipated Variation in Intravenous Methotrexate Dosing

Christopher S Parshuram, MB ChB D Phil

Staff Physician, Department of Critical Care Medicine; Investigator, Population Health Sciences, The Research Institute, Hospital for Sick Children; Assistant Professor, Faculty of Medicine, University of Toronto; Career Scientist, Ontario Ministry of Health and Long Term Care, Toronto, ON, Canada

L Lee Dupuis, B PharmSci

Pharmacist, Department of Pharmacy, Hospital for Sick Children

Teresa To, BSc MSc PhD

Senior Scientist, Program Head, Population Health Sciences, The Research Institute, Hospital for Sick Children; Associate Professor, Department of Public Health Sciences, University of Toronto; Investigator, Canadian Institutes of Health Research and Ministry of Health and Long Term Care; Associate Professor, Faculty of Medicine, University of Toronto

Sheila S Weitzman, MBChB

Staff Physician, Division of Haematology Oncology, Department of Pediatrics, Hospital for Sick Children; Associate Professor, Faculty of Medicine, University of Toronto

Gideon Koren, MD FABMT FRCP MBBS

Staff Physician, Division of Clinical Pharmacology and Toxicology, Department of Pediatrics, Hospital for Sick Children; Professor, Faculty of Medicine, University of Toronto

Andreas Laupacis, MD MSc

CEO, Institute of Clinical and Evaluative Sciences; Professor, Faculty of Medicine and Health Policy, Management and Evaluation, University of Toronto

Reprints: Dr. Parshuram, Department of Critical Care Medicine, Hospital for Sick Children, 555 University Ave., Toronto M5G 1X8, ON, Canada, fax 416/813-7299, christopher.parshuram{at}sickkids.ca

BACKGROUND: Studies using direct measurement suggest that the doses of up to 65% of drug infusions are outside industry standards. These preparation-associated errors occur despite routine safety procedures. As of April 5, 2006, the clinical impact of these errors had not been evaluated.

OBJECTIVE: To measure the occurrence and associated clinical outcomes of variations in intravenous methotrexate dosing.

METHODS: A prospective observational study was performed on 47 methotrexate infusions of 800 mg/m2 that were administered to 19 children with acute lymphoblastic leukemia. Serum methotrexate concentrations were measured at the end of the infusions, which were administered over 24 hours. The total methotrexate dose was determined by direct measurement of the concentration and the volume of each infusion.

RESULTS: Dosing errors greater than or equal to 10% occurred in 11 (23%) infusions and ranged from -61% to 55% of the ideal dose. Repeated measures regression analysis found the measured total methotrexate dose was not significantly associated with the serum methotrexate concentration (p = 0.58) or with clinical toxicities. The methotrexate dose administered over the last hours of infusion (p = 0.006) and the serum creatinine level at diagnosis (p = 0.05) were the most significant predictors of the methotrexate concentration. High methotrexate concentrations were significantly associated with increased hepatic aminotransferase levels; however, the degree of elevation was of limited clinical relevance.

CONCLUSIONS: While unexpected errors in drug dosing are more common than is suggested by other methods, the clinical impact observed in this model of methotrexate infusion was not demonstrably greater than medication errors described by other methods. Subsequent studies in this model of dosing error will require larger sample sizes, and other drugs should be evaluated.

Key Words: adverse drug event, medication error, methotrexate

Published Online, April 25, 2006. www.theannals.com, DOI 10.1345/aph.1G334


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C. S. Parshuram MB ChB DPh, T. To PhD, W. Seto BScPhm Pha, A. Trope MSc RPh, G. Koren MBBS, and A. Laupacis MD MSc
Systematic evaluation of errors occurring during the preparation of intravenous medication
Can. Med. Assoc. J., January 1, 2008; 178(1): 42 - 48.
[Abstract] [Full Text] [PDF]




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