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To the Editor:
—Your recent editorial on the treatment of herpetic keratitis was viewed with some concern by those of us who are working with 5-iodo-2'-deoxyuridine (IDU) and similar antimetabolites. To say that such a drug is nontoxic belies our knowledge of its mode of action.In order for an analog such as IDU to interfere with synthesis of viral desoxyribonucleic acid (DNA) it must necessarily also interfere with synthesis of cellular DNA. Consequently any cell of the body in preparation for division—and therefore synthesizing DNA and ribonucleic acid (RNA)—may be damaged by the presence of IDU, providing its concentration is sufficient to insure its utilization in preference to normal deoxyuridine. Obviously the therapeutic dose is by definition a toxic dose for the particular cell involved.Should one attempt treatment of systemic viral infections with adequate amounts of such drugs he surely would court disaster. It appears that IDU offers
Nelson EL. IDU. Arch Ophthalmol. 1962;67(5):691-692. doi:10.1001/archopht.1962.00960020691036