Lateral Gaze Nystagmus in Carbamazepine-Treated Epileptic Patients

Publisher Website
Google Scholar
Abstract
The incidence of lateral gaze nystagmus and its correlation with free and total plasma concentrations of carbamazepine (CBZ) an carbamazepine-10,11-epoxide (CBZ-E) were examined in 97 epileptic patients receiving chronic treatment with CBZ alone (n = 54) or in combination with phenobarbital (PB) (n = 43). All patients had plasma CBZ concentrations within the clinically optimal range (< 50 .mu.mol/L). Nystagmus was seen in 26% of patients receiving monotherapy and in 33% receiving combination therapy. Within each group, however, nystagmus was much more frequent among patients with higher CBZ concentrations. For patients receiving PB in combination the CBZ levels above which nystagmus was particularly frequent appeared to be lower than in the monotherapy patients, a finding that could not be attributed to differences in plasma PB concentrations. The correlation of CBZ-E levels (or the sum of CBZ + CBZ-E) with the occurrence of nystagmus was no better than that observed with CBZ levels alone. Free drug levels did not appear to be superior to total levels in discriminating between patients with or without nystagmus. The occurrence of nystagmus is concentration-dependent within the therapeutic plasma CBZ concentration range and threshold at which this neurological sign appears is reduced in the presence of PB, possibly as a result of a pharmacodynamic interaction.