Serum phenobarbital and barbital concentrations in rats on a limited food regimen.

Serum barbiturate levels were tracked for several hours in food deprived rats given 40, 60 or 80 mg/kg (SC) of either phenobarbital or barbital. All 3 phenobarbital doses produced peak serum drug levels at 1.5 hr postinjection. Serum barbital concentrations peaked 3 hr after both 60 and 80 mg/kg barbital doses while the 40 mg/kg dose produced a stable low drug level throughout the 4 postinjection hours. For both barbiturates administered, 40 mg/kg doses produced lower serum drug levels than either 60 or 80 mg/kg. The differences in serum drug concentrations between the latter two dose levels were inconsistent over time.