['We evaluated the efficacy of prophylactic valproic acid treatment (6 months) on the frequency of migraine attacks and the number of migraine headache days with respect to serum levels.', 'Valproic acid, a GABAergic drug, has been shown to be effective for migraine prophylaxis. Results from several dose- and serum level-adjusted studies have recommended valproic acid doses within a range of 500 to 1500 mg per day for migraine prophylaxis.', 'In this prospective open-label study, 52 patients received valproic acid doses of 300 to 1200 mg per day; 45 patients were treated per protocol. Valproic acid serum levels increased linearly in relation to the valproic acid dose and were between 21 and 107 microg/mL at the end of the treatment period. Patients were divided into two groups: those with valproic acid serum levels less than 50 microg/mL (group 1) and those with serum levels greater than 50 microg/mL (group 2).', 'The frequency of migraine attacks was significantly reduced in group 1 from 3.5 +/- 0.9 to 2.0 +/- 0.9 attacks per month. Migraine headache days also decreased (6.4 +/- 3.5 to 4.6 +/- 2.9 days per month). In the high serum level group, a reduction of migraine attacks from 3.5 +/- 0.9 to 2.8 +/- 1.0 attacks per month and only a slight decrease in headache days (6.4 +/- 3.5 to 6.1 +/- 2.4 days per month) was observed. The outcome of group 1 (low serum level) was significantly better than that of group 2 with respect to both parameters (P<.05). Side effects were generally mild and temporary.'] Is valproic acid effective in migraine prophylaxis at low serum levels : a prospective open-label study?