The stability of anticonvulsant drugs in whole blood.

The stability of four commonly used anticonvulsant drugs, viz., valproic acid, carbamazepine, phenytoin, and phenobarbital in whole blood was investigated after storage at conditions simulating storage and transport from outlying rural clinics. Storage conditions included 24 h at 23-25 degrees C, 24 h at 37 degrees C, 48 h at 37 degrees C, and 48 h at 23-25 degrees C. Valproic acid, carbamazepine, and phenobarbital were stable for 48 h at both storage temperatures. Phenytoin was stable at 23-25 degrees C for 48 h. However, small but statistically significant decreases in phenytoin concentrations were observed in samples that were stored for 24 h or longer at 37 degrees C. These changes may not be clinically significant.