|
| |
| Anticonvulsants |
| Overview |
 | Anticonvulsants differ substantially in terms of side effects, pharmacokinetic properties, and cost. |
| Treat with one drug if possible
 | More drug may cause increased side effects, due to drug interactions, not necessarily
from "toxic" blood concentrations of either drug. |
|
| First drug tried: about 60% of patients achieve satisfactory control
| Second drug used alone: about 55% respond |
| Of the remaining patients, only half have better control of seizures with two drugs. |
|
| Drug levels
| The older AEDs (phenytoin, carbamazepine, phenobarbital) have narrow, well-defined therapeutic
ranges |
| Individual patients vary in terms of the concentration which is effective and
that which causes toxic symptoms. |
| May be useful for
 | suspected noncompliance |
| lack or loss of therapeutic effect |
| suspected toxicity |
| suspected alteration of metabolism by a secondary disease,
changing physiological state (e.g. pregnancy); drug-drug
interaction |
| need for medicolegal verification of treatment |
|
|
|
| Choice of anticonvulsant based on
seizure type |
| Most important aspect of choosing a drug for
epilepsy is classifying the seizure type correctly. |
| Partial and secondarily generalized seizures
| Carbamazepine, phenytoin, primidone, and phenobarbitalare equally effective |
| For each individual patient one drug may be effective when another is not. |
| Valproate is effective for secondarily generalized seizures, but it is less effective in treating simple or complex partial seizures. |
|
| Generalized-onset seizures
| respond well to valproate. |
| Lamotrigine, topiramate, and zonisamide are reasonable alternatives. |
| Infrequently, carbamazepine, phenytoin,
tiagabine, or gabapentin may aggravate myoclonic and absence seizures. |
|
|
| Other factors
influencing choice of anticonvulsant |
| Phenobarbital and primidone:
| rarely used now as initial therapy |
| high incidence of sedation and cognitive side effects. |
|
| Phenytoin
| occasional undesirable cosmetic effects |
| gingival hypertrophy, hirsutism, and coarsening of facial
features |
| less preferable in young
women for long term use |
|
| Phenytoin and zonisamide have relatively long
half-lives
| once daily dosing. |
| may be preferable in patients with poor compliance. |
|
|
| Further reading |
|
|
|
