Phase I clinical study with pharmacokinetic analysis of 2-beta-D-ribofuranosylthiazole-4-carboxamide (NSC 286193) administered as a five-day infusion.

A Phase I trial of 2-beta-D-ribofuranosylthiazole-4-carboxamide (NSC 286193, tiazofurin) was conducted using a 5-day continuous infusion schedule. Twenty-four patients with advanced cancer were entered on this trial. Dose levels ranged from 360 to 2350 mg/sq m/day for 5 days. Neurotoxicity was dose limiting and occurred in six patients. Neurotoxicity was expressed as confusion, lethargy, or obtundation and was associated with focal neurological deficits in four of six patients: hemiparesis, three; cortical blindness and bilateral upper extremity weakness, one. Neurotoxicity was not clearly dose related, occurring at 900 mg/sq m/day for 5 days (two patients), 1100 mg/sq m/day for 5 days (two patients), 1850 mg/sq m/day for 5 days, and 2350 mg/sq m/day for 5 days (one patient each). Other toxicities seen were myelosuppression, desquamation of palms and soles, malar erythema, and hyperpigmentation, stomatitis, chest pain, drug fever, and increased serum creatine phosphokinase. Administered drug [71.5 +/- 11.2% (SE)] was recovered intact in the urine within 24 h of administration. Terminal-phase mean harmonic half-life was 8.0 h. The unpredictable neurotoxicity seen following continuous infusion therapy with tiazofurin suggests that Phase II trials of this schedule are not indicated until better understanding of the biochemical effects of tiazofurin is achieved.