Effect of timing of blood collection on serum phenobarbital concentrations in dogs with epilepsy.
OBJECTIVE
To determine whether there are therapeutically relevant changes in serum phenobarbital concentrations throughout a daily dosing interval in epileptic dogs receiving phenobarbital for > or = 3 weeks.


METHODS
Prospective study.


METHODS
33 epileptic dogs receiving phenobarbital.


METHODS
Serum phenobarbital concentrations were measured at 0 hour (trough), 3 hours, and 6 hours after oral administration of phenobarbital in epileptic dogs that had received phenobarbital twice daily for a minimum of 3 weeks. For each dog, trough, 3-hour, and 6-hour serum phenobarbital concentrations were evaluated to determine whether they were within the same therapeutic category (lower, middle, or upper end of the therapeutic range of 15 to 45 micrograms/ml), or whether there was a > 30% change in serum concentrations throughout the day.


RESULTS
Ninety-one percent (30/33) of dogs had trough, 3-hour, and 6-hour serum phenobarbital concentrations in the same therapeutic category. Only 9% (3/33) of dogs had trough, 3-hour, and 6-hour serum concentrations in different therapeutic categories with a > 30% change in concentrations throughout the day. Significant differences were not detected among mean serum phenobarbital concentrations when comparing the trough, 3-hour, and 6-hour samples for all dogs.


CONCLUSIONS
There is no therapeutically relevant change in serum phenobarbital concentrations throughout a daily dosing interval in most epileptic dogs. Therefore, timing is not important when collecting blood samples to measure serum phenobarbital concentrations in most epileptic dogs treated long-term with phenobarbital.
Levitski
R E
RE
Department of Medical Sciences, School of Veterinary Medicine, University of Wisconsin, Madison 53706, USA.
Trepanier
L A
LA
D000284:Administration, Oral; D000818:Animals; D000927:Anticonvulsants / Q000008:administration & dosage / Q000097:blood / Q000493:pharmacokinetics*; D001800:Blood Specimen Collection / Q000662:veterinary*; D004283:Dog Diseases / Q000188:drug therapy / Q000378:metabolism*; D004285:Dogs; D004827:Epilepsy / Q000188:drug therapy / Q000378:metabolism / Q000662:veterinary*; D006207:Half-Life; D010634:Phenobarbital / Q000008:administration & dosage / Q000097:blood / Q000493:pharmacokinetics*; D011446:Prospective Studies; D013810:Therapeutic Equivalency; D013997:Time Factors
D000927:Anticonvulsants; D010634:Phenobarbital