Initial: orally 200 mg in 2 equal doses on day 1, then 100 mg on day 2. Maintenance: 50-150 mg/day.

Experiments for determination of inhibition of vitamin-K-dependent carboxylation was determined using preparation of rat liver microsomes. Experimental reaction mixtures contained both vitamin K and a vitamin K antagonist. The control reaction mixture contained 3.00 ml of microsomal suspension, 0.81 ml of buffer II. 1.20 ml of an ATP-generating system, 0.60 ml of NADH (final concentration 2 mM), 0.30 ml of dithiothreitol (final concentration 7 m.V/) in buffer II. 0.060 ml of NaH[14C]O3 (1.0 uCi/uL added 0.5 min prior to reaction initiation) and at the time of reaction initiation 0.030 ml of vitamin K (final concentration 20 ug/ml) diluted in 0.85% sodium chloride solution. Reaction mixtures were equilibrated at 27 °C in a reciprocating shaker water bath at 100 excursions per minute. Serial samples (0.45 ml each) were collected from each control and blank reaction tube at 2,4, 6, 8, 10, 12, 14, 16, 30, 60, 90 and 120 min, and from each experimental reaction tube at 2,4, 6, 8, 10, 12, 14 and 16 min. Each sample was transferred to a tube containing I ml of ice-cold 10% TCA. Amount of product formed was determined using liquid scintillation spectrometer with the external standard method of quench correction. Phenindione inhibits Vitamin K-dependent carboxylation with IC50 of 19 uM.