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
Although there is no information regarding the time lapse between phenobarbital ingestion and ER admission, we might "guess" that the blood level approximates C0 and is certainly no higher. With such an assumption, the dose ingested is given by:Dose=C0xVd /f=50mg/Lx40L/1=2000mg=2g
100 mg
500 mg
1 g
2 g
C.N.S