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Monitoring Clozapine: Are Fingerprick Blood and Plasma Clozapine Levels Equivalent to Arm Venipuncture Blood and Plasma Levels?

Goossen, Randolph B.*; Freeman, David J.; Satchell, Anne Marie*; Urquhart, Bradley L.

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The objective of this pilot study was to determine whether fingerprick blood and plasma clozapine levels were equivalent to arm venipuncture blood and plasma levels for the purpose of therapeutic monitoring. A convenient sample of 10 outpatients from the Elgin Program of Assertive Community Treatment Team (PACT) participated in the study. Blood samples were obtained simultaneously from both the arm and finger in patients at steady state to measure clozapine levels. Each site provided a blood and plasma clozapine level, and they were compared. Clozapine levels from arm and finger sites were found to be equivalent in both blood and plasma. Although plasma clozapine levels were consistently greater than those in whole blood by a mean value of 27%, the plasma therapeutic threshold level (350-400 μg/L) was considered an adequate target for monitoring. A fingerprick blood sample of 50 μL was sufficient to measure clozapine levels accurately at steady state. We therefore concluded that fingerprick blood testing is as effective as the traditional arm venipuncture method in obtaining accurate clozapine levels. This procedure may provide certain benefits for the seriously mentally ill.

*Program of Assertive Community Treatment, Elgin County, University of Western Ontario, St. Thomas, Ontario, Canada; and Departments of Medicine and Physiology-Pharmacology, University of Western Ontario, London, Ontario, Canada

Received October 25, 2002; accepted March 11, 2003.

Address correspondence and reprint requests to Randolph B. Goossen, Psyc Health Centre, Pz-239-77, Bannatyne Avenue, Winnipeg, Manitoba, Canada R3E 3N4; E-mail: rgoossen@wrha.mb.ca

© 2003 Lippincott Williams & Wilkins, Inc.