A) Estimated fVIII t1/2 from Day 1 or Day 2 time points for a single pt. fVIII levels drawn on first day (up to 6 hours post infusion) predict t1/2 = 4.7 h. Day 2 levels (> 24–48 post infusion) demonstrate t1/2 = 7 h. (p for difference = 0.047). Due to apparent biphasic elimination kinetics, day 2 data better predict terminal half-life. B) Half-life estimation in an 18 y.o. pt using day 2 PK levels, demonstrating prolonged fVIII survival.