Bioavailability of rectally administered carbamazepine suspension in dogs

The relative bioavailability of an investigational carbamazepine suspension was studied following rectal administration in dogs. Doses of carbamazepine, 20 mg/kg, were given to six dogs. The routes of administration were oral tablet, oral suspension, and rectal suspension. There was no significant difference (p greater than 0.05) in total absorption, as indicated by the area under the serum concentration-time curve between the oral and rectal suspensions. The notable differences between the oral suspension and the rectal suspension were in the maximum serum concentration achieved and the time to achieve this maximum serum concentration. This is due to a prolonged absorption of carbamazepine given rectally, which may limit the ability to achieve therapeutic serum concentrations rapidly. Carbamazepine suspension given rectally may be a satisfactory alternative when administration by the oral route is not possible.