| There are far more anti-convulsants drugs available that the average physician can use effectively, and even Neurologists today use a very limited range. The aim is to suppress fits by an effective concentration of drug in plasma (and hence the brain) at all times. (Careful dose- adjustment is necessary to achieve this and best results can be achieved with a single drug in 90% of cases. The old idea of adding drug after drug is now known to be much less satisfatory. The principle therefore is to start with an “average” dose, modified if the patient is very large, very small, has liver damage or any other features which would affect dose-response. The dose may then be increased until fits are controlled. The balance between control of fits and side effects of overdose, requires care on the physician’s part and cooperation and com- pliance on the patient’s part.The need for compliance must be emphasized repeatedly. Dose Frequency and Compliance Most anti-epileptics can be given twice daily or even as a single dose at night. Three times daily regime is usually unnecessary and results in poor compliance as middday doses are most often forgotten. Three times daily regime is usually only needed if large doses are causing transient side effects associated with high peak levels. Therapeutic Drug Monitoring Optional plasma levels are now well established, and drug monitoring is now possible at the Queen Elizabeth Hospital for phenytoin, phenobaritone and carbamazepine. Plasma measure-ments are usually needed in three situations: (i) to check compliance, if poor compliance is suspected; (ii) if fits are poorly controlled in spite of moderate to large doses; (iii) if drug toxicity is suspected. Therapeutic blood levels are: Phenytoin 10 - 20mcg/ml Phenobarbitone 15 - 40mcg/ml Carbamazepine 4 - 10mcg/ml Drug Interaction Anti-epileptics are especially prone to interactions with other drugs e.g. through induction or inhibition of metabolism. |
