Anticoagulation with sodium warfarin in children: effect of a loading regimen.

To assess dose requirements of warfarin in children, we analyzed retrospectively the treatment of 26 patients with the drug. Subsequently we treated 15 children, prospectively, with a regimen derived from our retrospective analysis (0.2 mg/kg/day for 2 days). In the retrospective analysis we found the prothrombin time (PT) at day 2 to correlate significantly with the dose given on day 0 (p less than 0.001) and with the cumulative dose on days 0 and 1 (p less than 0.001), but the standardized loading regimen resulted in a wide range of PTs independent of age, weight, or body surface area. The warfarin dose contributes only 40% of the variability in PT; an individual child's response to warfarin cannot be predicted accurately on the basis of the usual morphometric measurements.