antibioticsbooks

176 PART 4 Antifungal Drugs
Adverse Effects
Flucytosine, which is also called 5-FC, is fluorouracil
for fungi. When this fact is considered, the
adverse effects are predictable. Flucytosine is only
relatively selective for fungi and can cause considerable
bone marrow suppression, particularly in
higher doses or during prolonged courses. GI complaints
are more common, but they are less severe.
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Important Facts
• Drug concentration monitoring is available for
flucytosine: check a peak concentration about
two hours after the dose is given. However, do
not rely on flucytosine concentrations alone to
monitor for toxicity—hematology values are
more important than drug levels.
• Flucytosine generally should not be used as
monotherapy for invasive candidiasis because
of the potential emergence of resistance in vivo.
• The most common use for flucytosine is in combination
with an amphotericin B formulation
for cryptococcal meningitis. Though this combination
is recommended in guidelines and very
common, some clinicians have questioned the
value of flucytosine. In an early clinical study
for this indication, flucytosine use was associated
with more rapid sterility of cerebrospinal
fluid cul tures but showed no obvious clinical
benefit. However, more recent studies have
shown a survival benefit with flucytosine use.
This is obviously a plus in terms of efficacy,
but flucytosine is difficult to obtain or afford in
resource-poor countries where HIV infection is
highly endemic.