['To compare the pharmacokinetics and efficacy of oral versus intravenous mixed micellar vitamin K prophylaxis in infants with cholestatic liver disease, a known risk factor for vitamin K deficiency bleeding.', 'Prospective randomised controlled study.', 'Paediatric Liver Unit.', 'Forty four infants less than 6 months of age with conjugated hyperbilirubinaemia.', 'Serum concentrations of vitamin K(1) and undercarboxylated prothrombin (PIVKA-II; a sensitive functional indicator of vitamin K status) before and for up to four days after a single dose of mixed micellar K(1) 1 mg intravenously or 2 mg orally. Comparison of K(1) levels 24 hours after oral K(1) with those from 14 healthy newborns given the same dose.', 'At admission, 18 infants (41%) had elevated levels of serum PIVKA-II and eight (18%) had low K(1) concentrations, indicative of subclinical vitamin K deficiency. Median serum K(1) concentrations were similar in the oral and intravenous groups at baseline (0.92 v 1.15 ng/ml), rising to 139 ng/ml six hours after intravenous K(1) but to only 1.4 ng/ml after oral administration. In the latter group, the low median value (0.95 ng/ml) and wide range (< 0.15-111 ng/ml) of serum K(1) compared unfavourably with the much higher levels (median 77, range 11-263 ng/ml) observed in healthy infants given the same oral dose, and suggested impaired and erratic intestinal absorption in cholestatic infants. The severity of malabsorption was such that only 4/24 (17%) achieved an incremental rise in serum K(1) > 10 ng/ml.'] Is intestinal absorption of mixed micellar phylloquinone ( vitamin K1 ) unreliable in infants with conjugated hyperbilirubinaemia : implications for oral prophylaxis of vitamin K deficiency bleeding?