When should the blood sample be collected for THERAPEUTIC MONITORING of PHENOBARBITAL?
There is no significant difference between serum phenobarbital concentrations in samples obtained prior to dosing, or at 3 or 6 hours postpill. Thus, when you are monitoring therapeutic serum phenobarbital concentrations in dogs, you can collect a sample at any time of the day as long as: 1) the dose has been constant for at least 7 days; 2) the dog is not receiving any drugs that would alter the P450 enzymes (cimetidine); and 3) the dog is receiving < 8 mg/kg/day of phenobarbital.
