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Is there someone out there who has experience with dosing of flucytosine?
From what I know and have read, peak levels >125 mg/L are toxic (bone marrow
supression and hepatotoxicity) and those
<50 mg/L would be at risk of developing resistance.
We see very few patients here at DHMC who receive 5-FC (and amphotericin)
but always seem to have problems with their regimens, mostly because we mail
out the drug samples and do not have results back until 48-72 hours later.
Any and all assistance is welcome. Thank you.
Marc Semprebon, RPh, MSLS
Dartmouth-Hitchcock Medical Center
Lebanon, NH 03756
(603) 650-5000 pager #9827
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The data linking serum concentrations of 5FC with efficacy or toxicity are,
as for many drugs, anecdotal. Generally we try to maintain serum
concentrations (we usually draw a random sample midway through the dosing
interval) of around 70-80 mcg/mL.
One should continue to monitor platelet and WBC counts, even when
concentrations are within the "normal" range. Some literature suggests that
5FC is converted to 5FU by intestinal bacteria/yeasts which contain cytosine
deaminase, rather than this conversion occurring in plasma. Therefore,
factors other than serum 5FC concentration (e.g., duration of therapy) may
be more important vis a vis toxicity.
Steven C. Ebert, Pharm.D., FCCP
Clinical Specialist, Infectious Diseases
Clinical Associate Professor of Pharmacy
Department of Pharmacy, Meriter Hospital
202 S. Park Street
Madison, WI 53715
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