Monograph: |
Idoxuridine
Odourless or almost odourless, colourless crystals or a white
or almost white crystalline powder from which iodine vapour
is liberated on heating. M.p. about 180Β°. with decomposition.
Slightly soluble in water and in alcohol: practically insoluble
in chloroform and in ether: dissolves in dilute solutions of al-
kali hydroxides. A 0.1 % solution in water has a pH of 5.5 to
6.5. It has been reported that some decomposition products
such as iodouracil are more toxic than idoxuridine and reduce
its antiviral activity. Store in airtight containers. Protect
from light.
Adverse Effects
Adverse effects which occur occasionally when idoxuridine
is applied to the eyes include irritation, pain. conjunctivitis.
oedema and inflammation of the eye or eyelids, photophobia,
pruritus. and rarely, occlusion of the lachrymal duel. Hyper-
sensitivity reactions may occur rarely. Prolonged use inav
damage the cornea.
Idoxuridine applied to the skin may produce irritation and hy-
persensitivity reactions. Excessive application of topical
idoxilridine to the eyes or skin may cause punctate defects in
lhe cornea or skin maceration.
Adverse effects after intravenous administration of idoxurid-
ine have included bone-marrow depression and liver damage.
Idoxuridine is a potential carcinogen and teratogen.
Squamous carcinoma in one patient was associated with top-
ical idoxuridine treatment. Reference is made to one earlier
similar case.
Precautions
Idoxuridine should he used with caution in conditions where
there is deep, ulceration involving the stromal layers of the
cornea, flayed healing has resulted in corneal perforation.
Prolonged topical use should be avoided.
Idoxuridine's potential teratogenicity should be taken into ac-
count when treating pregnant patients or patients likely to be-
come pregnant. Corticosteroids should be applied with
caution in patients also receiving idoxuridine as they may ac-
celerate the spread of viral infection. Boric acid preparations
should not be applied to the eye in patients also receiving oc-
ular preparations of idoxuridine as irritation ensues,
Antiviral Action
Following intracellular phosphorylation to the triphosphate.
idoxuridine is incorporated into viral DNA instead of thyrni-
dine so inhibiting replication of the virus. Idoxuridine is also
incorporated into mammalian DNA. Idoxuridine is active
against herpes simplex and varicella zoster viruses. It has also
been shown to inhibit vaccinia virus and cytomegalovirus.
Resistance to idoxuridine occurs in vitro and in vivo.
Pharmacokinetics
Penetration of idoxuridine into the cornea and skin is reported
to be poor. Following systemic administration idoxuridine is
rapidly metabolised to iodouracil, uracil and iodide.
Uses and Administration
Idoxuridine is a pyrimidine nucleoside structurally related to
thymidine. It has been used topically in the treatment of her-
pes simplex keratitis and cutaneous forms of herpes simplex
and herpes zoster, but has generally been superseded by other
antivirals .
In the treatment of herpes simplex keratitis idoxuridine has
been applied as a ophthalmic solution.
Idoxuridine 5% in dimethyl sulphoxide (to aid absorption)
can be painted onto the lesions of cutaneous herpes simplex
and herpes zoster four times daily for 4 days.
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