Drug therapy reviews: clinical pharmacology of antiepileptic drugs.

The absorption, distribution, biotransformation, excretion and clinical pharmacokinetics of antiepileptic drugs are reviewed. Six guidelines for the therapeutic use of these drugs are given: (1) when therapy with an antiepileptic drug is initiated or when dosage is raised or lowered, the new steady-state drug serum concentration and the full effect of the dosage change will not occur for five elimination half-lives; (2) a loading dose is usually necessary to immediately achieve a steady-state serum drug concentration equal to the usual maintenance steady-state serum drug concentration; (3) the choice of dosage intervals for antiepileptic drugs is determined in part by the range of fluctuation in drug concentration between doses that is acceptable; (4) addition of a drug to an existing antiepileptic regimen may raise or lower the serum concentration of prior drugs by inhibition or induction of their metabolism; (5) if possible, make only one change at a time in an antiepileptic drug regimen; and (6) antiepileptic drugs should not be given by the i.m. route in emergency situations.