Purpose: Valerian root ( Valeriana officinalis L.) has been used since antiquity as a medicinal herb. Recent studies have found that certain herbal products used concomitantly with conventional therapeutic products can markedly affect drug disposition.
Methods: The in vitro effect of aliquots from 14 commercially available single-entity and blended products containing valerian root on cytochrome P450 CYP3A4-mediated metabolism and P-glycoprotein transport has been determined with aqueous, ethanol and acetonitrile extracts.
Results: Hydroxyvalerenic acid, acetoxyvalerenic acid and valerenic acid content was analyzed and wide variation was found between samples and compared to the concentrations noted on the product labels. Valerian extracts from the products tested also exhibited a marked capacity to inhibit cytochrome P450 3A4-mediated metabolism and P-glycoprotein transport based upon the ATPase assay.
Conclusions: There is wide variation between commercially available samples of valerian root. The findings from this study suggest that valerian root may have an initial inhibitory effect when taken with therapeutic products. Further work is warranted to determine whether valerian root can affect other CYP450 isozymes and how the results of this in vitro investigation can be extrapolated to in vivo situations.