Abstracts

Patients who did not respond to carbamazepine (CBZ) or who developed side effects with CBZ were switched to oxcarbazepine (OXC), a newer antiepileptic drug (AED). This study looked at the effect of switching these patients to OXC. A total of 424 charts of patients attending the outpatient clinic from January 2000 to September 2003 were reviewed retrospectively. Patients on CBZ, who were converted to OXC monotherapy or who had OXC added to their existing AED regimen were identified and the data collected and analyzed. Demographics, seizure severity, side effects, dose of AEDs, concomitant medications, failed AEDs, sodium levels, OXC plasma levels and EEG findings recorded at each visit were reviewed. A total of 154 patients had been switched from CBZ to OXC, 61 were on CBZ polytherapy and 93 were on CBZ monotherapy on their first visit. Ninety-three were female and 61 were male. The average age at onset of seizures was 19 yrs. In the whole group, 1(1%) had worsening of seizures, 49 (32%) had decreased severity of seizures, 78 (51%) became seizure free, 20 (13%) showed no change and there was no information available for 6 (4%).
Among the 61 patients on CBZ polytherapy, 21(34%) could be converted to OXC monotherapy while 40 (66%) had OXC added to their polytherapy regimen. Among the 93 patients on CBZ alone, 82 (88%) were converted to OXC monotherapy and 11(12%) had OXC added on. Of the 103 patients converted to OXC monotherapy, 65 (63%) were seizure free, and 21(20%) had decreased severity. Of the 51 patients for which OXC was added, 13(25%) were seizure free and 25(49%) had decreased severity.
Side effects developed in 78(51%) of the patients ranging from mild to severe, and 13(8%) of these had to stop their treatment. Thirteen patients (8%) who were switched from CBZ to OXC, had to be switched back to CBZ due to side effects from OXC. Three of these developed rashes and the remaining developed side effects such as diplopia, dizziness and lethargy. A total of 12 (8%) patients developed hyponatrenia (sodium[lt]125 mmol/L) however only 3 patients had to stop their treatment due to side effects related to the hyponatremia. Sodium levels ranged from 115- 153.
Oxcarbazepine levels ranged from 9-63[micro]g/ml. Patients with mild seizures appeared to require levels ranging from 10-20 [micro]g/ml, patients with moderate seizure severity required levels in the range of 20-30 [micro]g/ml and those with severe seizures levels above 30 [micro]g/ml. Of the 54 patients who had OXC levels above 30, 20(37%) were seizure free, 24(44%) had decreased severity and 9(17%) showed no change. However, 32(59%) of these patients developed side effects which resolved over time in all but 1 patient who had to discontinue OXC. OXC can be safely used for conversion to monotherapy or as add-on in patients already on CBZ. Plasma levels of OXC appear to correlate with the severity of seizures. (Supported by Unrestricted grant from Novartis Pharmaceutical Corporation)