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Pharmacokinetics and Pharmacodynamics of Peldesine (BCX‐34), a Purine Nucleoside Phosphorylase Inhibitor, following Single and Multiple Oral Doses in Healthy Volunteers

The pharmacokinetic parameters of peldesine (BCX‐34) were investigated after single and multiple oral doses in two groups of healthy adult volunteers. The pharmacodynamic elevation of endogenous inosine and 2′‐deoxyguanosine was simultaneously monitored. The first group of 8 subjects received an intravenous dose (18 mg/m2) and five oral doses (30, 63, 108, 144, and 192 mg/m2) of drug. A second group of 12 subjects received 160 mg/m2 in four and in six divided doses orally Serial blood samples and total urine outputs were collected during dosing and for at least 24 hours after the last dose was administered. One set of samples was analyzed using high‐pressure liquid chromatography/ultraviolet (LC/UV) methods, validated for intact drug in human plasma and urine samples. Another set of samples was analyzed for the biomarkers, inosine and 2′‐deoxyguanosine, using high‐pressure LC with either mass spectrometry (MS) or electrochemical detection (EC) methods. The pharmacokinetic parameters of inosine and 2′‐deoxyguanosine were calculated using noncompartmental methods and correlated against the pharmacokinetic parameters of BCX‐34. For the single‐dose study, the results exhibited linear pharmacokinetics over the dose range from 30 to 144 mg/m2. The calculated terminal half‐life was 3.5 ± 1.0 h, and the absolute bioavailability of the oral formulation was approximately 51%. Analysis of urine in the first 24 hours of collection accounted for approximately 82% of the absorbed intact drug. Evaluation of the multiple‐dose pharmacokinetics indicated that steady‐state blood concentrations were achieved by 24 hours when the drug was administered four or six times a day. A drug dose‐related elevation of plasma 2′‐deoxyguanosine was observed. This phenomenon was not seen with plasma inosine levels. However, analysis of urine samples showed an increase in inosine output with an increase in the drug dose. The calculated terminal half‐life of inosine and 2′‐deoxyguanosine was 15.3 ± 1.8 h and 1.3 ± 0.1 h, respectively.