A 40-year-old man was brought to the ER after ingesting an unknown quantity of phenobarbital, the plasma level of which was 50 mg/L on admission. Pharmacokinetic parameters for phenobarbital are: Vd=40 L, CL=6 L/day, half-life = 4 days, oral bioavailability f=1. The quantity of the drug that the patient ingested must have been close to