Anticonvulsants in Psychiatry: Their Similarities Are Different Part 2-Clinical Applications

Article excerpt

Issue All anticonvulsants reduce seizures but not all anticonvulsants have convincing therapeutic actions in bipolar disorder, anxiety disorders, chronic pain, or schizophrenia (1-10)

Actions Learn the therapeutic profiles of various anticonvulsants by examining both the evidence and the mechanistic rationale for using each agent in bipolar disorder, anxiety disorders, chronic pain, and schizophrenia

Benefits Knowing the similarities and differences among the anticonvulsants should improve the chances that a prescriber will select and combine the most effective agents for any given patient with any given disorder

The famous baseball star Yogi Berra was once asked whether he and his son were alike. He paused, scratched his head, and replied, "Yeah, we're alike. But our similarities are different." The same could be said about anticonvulsants, which are alike in that they are all effective at treating epilepsy, but are different in that they do not all have the same pharmacologic mechanisms of action. Neither do they have the same evidence for efficacy in multiple psychiatric disorders, such as bipolar disorder, anxiety disorders, chronic pain, and schizophrenia.

In the absence of data

Agents with proven efficacy in a given disorder, as determined by randomized controlled trials, should be prescribed first for that disorder. The trick to prescribing in the absence of data is to focus on mechanism of action. Even if an anticonvulsant does not yet have much evidence of efficacy, two agents with the same or similar mechanisms of action are likely to lead to similar therapeutic effects. On the other hand, anticonvulsants with different mechanisms of action will likely result in different therapeutic actions and side effects. This concept provides a rationale for off-label prescribing of second-line anticonvulsants that are approved for epilepsy but have not been adequately tested in another condition.

Anticonvulsants in bipolar disorder and schizophrenia

Controlled data demonstrate that valproate effectively treats acute mania (treating from above) and may prevent recurrence of manic episodes (stabilizing from above); preliminary data suggest it may also treat depression (treating from below) and prevent recurrence of depressive episodes (stabilizing from below). (6,10) Lamotrigine seems to best stabilize from below, and second-best to treat from below and stabilize from above. (6,10) Carbamazepine may also treat from above, but is less well investigated than valproate and lamotrigine. (6,10) Oxcarbazepine, which acts just like carbamazepine and at the same site as lamotrigine, may be expected to have useful actions in bipolar disorder, although this has not been proven. (6,10) Zonisamide may also have a mechanism of action that is similar to bipolar agents, and may therefore be an effective second-line choice. …