Pharmacokinetic Comparison of Two Formulations Containing Silymarin : Legalon cap. $140^{\circledR}$vs. a Generic Formulation

레가론캅셀 $140^{\circledR}$ 및 국내 generic 제형의 약동학적 특성에 관한 비교 연구

Background : Silymarin formulations show low bioavailability due to its poor solubility. Therefore, developing a formulation which could improve bioavailability was a major issue. In Korea, there are many kinds of silymarin-containing formulations, including Legalon cap. $140^{\circledR}$. We compared the pharmacokinetic characteristics of a generic silymarin formulation developed by H company with those of Legalon cap. $140^{\circledR}$. and speculated on the clinical implications. Methods : The study was conducted as a open-labeled, randomized, 2-way crossover Latin square design in 16 healthy subjects. Subjects were separated into two groups, A and B. Subjects in group A were administered a generic formulation orally, and 1 week later they were administered Legalon cap. $140^{\circledR}$. Subjects in group B were administered the drugs in opposite sequence in the same manner. Dosage administered was 60 mg as silibinin. Serial blood samples were collected till 24 hours after the drug administration. Plasma concentrations of silibinin diastereomers were assayed by HPLC and total silibinin concentrations were obtained. Pharmacokinetic parameters of the two formulations were analyzed by noncompartmental methods. We tested the sequence effect, period effect and differences of parameters between the two formulations by ANOVA. The pharmacokinetic characteristics of two test formulations were compared by 90% confidence intervals for ratios of $AUC_{0-\infty}$ and $C_{max}$, and the other kinetic parameters by student t-test. Results : Mean $AUC_{0-\infty}$ and $C_{max}$ of the generic formulation were 1.46 and 3.06 times higher than those of Legalon cap. $140^{\circledR}$, respectively $(AUC_{0-\infty}\;:\;3766{\pm}1475\;vs.\;2580{\pm}863\;ng{\cdot}hr/mL,\;C_{max}\;:\;1639{\pm}499\;vs.\;535{\pm}181\;ng/mL\;;\;generic\;vs.\;Legalon\;cap.\;140^{\circledR},\;mean\;{\pm}\;SD)$. The differences of $AUC_{0-\infty}$ and $C_{max}$ were statistically significant (p<0.001). $t_{max}$, MRT, and terminal half-life of the two drugs were also statistically different $(t_{max}\;:\;0.73{\pm}0.22\;vs\;1.67{\pm}0.98\;hr,\;MRT\;:\;5.38{\pm}1.65\;vs\;6.11{\pm}1.41\;hr,\;t_{1/2}\;:\;5.48{\pm}1.71\;vs.\;4.47{\pm}1.75\;hr,\;a\;generic\;vs.\;Legalon\;cap.\;140^{\circledR})$. The mean of individual relative bioavailability $(generic/Legalon\;Cap.\;140^{\circledR})$ was 1.46, and the 90% confidence interval was 1.31-1.62. The mean ratio of $C_{max}$ $(generic/Legalon\;Cap.\;140^{\circledR})$ was 3.1, and the 90% confidence interval was 2.47-3.82. Conclusion : The $AUC_{0-\infty}$ and $C_{max}$ of the new generic drug were significantly greater then those of Legalon cap. $140^{\circledR}$. The generic drug was rapidly absorbed, and the increase in oral bioavailability was primarily due to the increase in the early phase absorption. The two formulations were not bioequivalent, and the therapeutic equivalence needs to be evaluated. The clinical implications of greater $AUC_{0-\infty}$ and $C_{max}$ should be investigated by additional clinical studies. The dosage of the generic has not been established by clinical studies, in contrast to that of Legalon Cap. $140^{\circledR}$.