In vitro release of valerenic and hydroxyvalerenic acids from valerian tablets

Although most commercial valerian formulations are coated tablets not any comparison study of their drug release profiles has been published so far. The main objective of this work is to establish a drug release test suitable for studying and comparing different valerian tablets. Thus, hydroxyvalerenic and valerenic acid concentrations were assayed by HPLC using a C18 Kromasil (200 x 4.6 mm, 5 microm) column and a mobile phase containing methanol and an orthophosphoric acid solution 0.5% v/v in water at a ratio of 75:25 at a constant flow rate of 1 ml/min. Saturation solubilities for hydroxyvalerenic and valerenic acid at pH 6.8 were 26 +/- 5.1 and 1 +/- 0.6 microg/ml, respectively. Usually for drugs with such low solubility values, their oral absorption and hence bioavailability are limited by their dissolution characteristics. A dissolution test was conducted according to the general method 2 (paddles) of USP 24 using 500 ml buffer medium (pH 6.8) at 50 rpm. Five different formulations were studied and compared: one uncoated tablet formulation and four marketed coated tablets. The uncoated tablet formulation had the fastest release profile, whereas the coated tablets manifested very different release patterns, depending on the type of formulation. Because of these differences in drug release pattern not every tablet formulation may be appropriate for the same clinical indications. Clinical data are required to confirm the correlation between drug release pattern and the therapeutically value of each formulation.