Valpromide-amitriptyline interaction. Increase in the bioavailability of amitriptyline and nortriptyline caused by valpromide

Valpromide is largely used in the therapy of affective disorders for its presumed thymoregulating activity. So, it is often associated with tricyclic antidepressant treatment. Previous clinical studies lead us to consider the possibility of an interaction between valpromide and tricyclic antidepressants, interaction which could result in an increase of antidepressant plasma concentrations. But no pharmacokinetic study has been realized up to now in order to clearly demonstrate such a phenomenon. The authors studied amitriptyline and nortriptyline plasma levels in two groups of ten patients receiving 125 mg amitriptyline, once a day, during 20 days. In the second group, patients also received 600 mg valpromide daily after ten days on amitriptyline. In the first group amitriptyline and nortriptyline plasma concentrations remained stable between the tenth and the twentieth day. In the second group, addition of valpromide resulted in a significant increase of antidepressant plasma levels: from 70.5 +/- 35 to 105.5 +/- 49 ng/ml (p less than 0.0003) for amitriptyline, and from 61.0 +/- 34 to 100.5 +/- 65 ng/ml (p less than 0.01) for nortriptyline.