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resulting in severe nausea and vomiting in
persons who concurrently ingest alcohol. There
has been concern about possible carcinogenesis
and birth defects with metronidazole, but
neither has been documented in humans.
Nonetheless, metronidazole is not approved for
use during pregnancy.
Paromomycin
Paromomycin is an aminoglycoside antibiotic.
It is poorly absorbed after oral administration,
resulting in extremely high concentrations in
the lumen of the bowel, but not in the body. It
is effective because of its restricted area of distribution.
Paromomycin acts at the level of the
30S ribosome and inhibits protein synthesis. It
kills cysts of E. histolytica and is administered
with metronidazole in symptomatic amebiasis
and alone in persons with asymptomatic
infection. It is also active against another
enteric pathogen, Dientamoeba fragilis, and
it has been used topically to treat vaginal
trichomoniasis.
Side-effects with paromomycin are primarily
gastrointestinal. They include nausea, vomiting,
abdominal cramps and diarrhea. A small
amount of paromomycin is absorbed and
cleared through the kidney. Renal toxicity and
ototoxicity can occur, particularly in patients
with underlying renal disease. Pancreatitis has
been reported in the setting of AIDS.
Iodoquinol
Iodoquinol (diiodohydroxyquin), a halogenated
oxyquinoline, is a luminally active drug that
kills cysts of E. histolytica and is effective in the
treatment of D. fragilis and B. coli. The mechanism
of action is unknown. The side-effects
include nausea, vomiting, diarrhea, headache,
abdominal pain, fever and itching. On occasion
iodine-related dermatitis develops. Seizures
and encephalopathy are rare. Because of the
high iodine content, iodoquinol can interfere
with thyroid function tests for months after
administration. It is contraindicated in anyone
with iodine intolerance. Optic nerve damage or
inflammation and peripheral neuropathy can
occur after prolonged administration of high
doses. The recommended dosage should not be
exceeded.
Diloxanide furoate
Diloxanide furoate, a substituted acetanilide,
is also effective in eradicating cysts of E. histolytica
following treatment with metronidazole
for invasive amebiasis or when used
alone in asymptomatic infection. Its mechanism
of action is unknown. The most common
side-effect is flatulence and mild gastrointestinal
disturbances. Serious untoward effects are
rare at the recommended doses. While not
approved for use in the United States, the low
cost of diloxanide furoate makes it an attractive
alternative in developing countries.
Furazolidone
Furazolidone, a nitrofuran derivative, is the
only drug for giardiasis that is available in
liquid form. The precise mechanism of action
is not known, but furazolidone is thought to
damage the parasite’s DNA. Common sideeffects
include nausea, vomiting, diarrhea and
fever. Rare side-effects include hypotension,
urticaria, serum sickness, mood disorders and
hypersensitivity reactions. Mild to moderate
hemolysis may occur in patients with G-6-
PD deficiency. Like metronidazole, furazolidone
has disulfiram-like activity. It is also a
monoamine oxidase inhibitor. It should not
be given to breast-feeding mothers because
MEDICAL APPLICATIONS