Most adult patients with refractory epilepsy have partial (focal) seizures with or without secondary generalisation. During the 1970s and early 1980s studies showed that in 70-80% of adults with newly diagnosed epilepsy, seizures were controlled successfully by carefully monitored monotherapy with any of the four standard antiepileptic drugs—phenobarbital, phenytoin, carbamazepine, or sodium valproate—all of which seemed to have similar efficacy in partial epilepsy in later comparative trials of monotherapy.1^–4 Furthermore, adding a second drug for patients with continuing seizures on optimum monotherapy led to modest benefit in no more than one third, a deterioration in seizure control or unacceptable toxicity in about a quarter, and no change in the rest.2 5

These studies led to important questions. Should patients unresponsive to the optimum use of the first drug be switched to alternative monotherapy or treated with polytherapy? If so, …