The clinical pharmacology of 5-iodo-2′-deoxycytidine (ICDR) has been investigated in twelve patients with advanced neoplastic disorders and compared with that of 5-iodo-2′-deoxyuridine (IUDR).

Studies of the catabolism of ICDR-I125 in four of these patients revealed that between 85 and 98 per cent of this compound was deaminated, with subsequent cleavage of the formed IUDR to 5-iodouracil, which, in turn, was de-iodinated, with the formation of iodide.

Objective evidence of inhibitory effects on various rapidly growing normal tissues was noted after treatment with ICDR and included stomatitis, hair loss, nail changes, and hematopoietic depression similar to that observed after administration of IUDR.

In those patients in whom metabolic studies with ICDR-I125 were performed, and in whom an adequate maintenance of blood levels of IUDR-I125 did not occur, typical signs of toxicity were not seen, and significant antineoplastic effects were not produced. In one patient in whom sustained blood levels of IUDR-I125 resulted from the ICDR-I125 injected, a marked regression of a carcinoma of the vulva was obtained repeatedly on four occasions. Both the antineoplastic effects and the manifestations of toxicity observed in this patient were comparable to those seen after an identical course of therapy with IUDR-I125.

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These studies were supported by a special grant provided jointly by the American Cancer Society and its Connecticut division, as well as by grants of the Public Health Service (CY-2817, CRTY-5138, CY-5262, CA-05944, and OG-14).

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