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Dear Editor

With regard to the recent review on milk thistle and its use in the treatment of liver disease, we would like to highlight an errant omission in the footnotes of this review, in which numerous beneficial actions of silibinin phosphatidylcholine complex (SPC) for liver health are cited but no mention was made of Marin®, an SPC product from Nutramax Laboratories, Inc.[1] This omission is especially critical, as most of the referenced companion animal studies in this recent review on milk thistle used Marin, the earliest SPC product available to veterinarians, in their studies. Studies using Marin provide compelling evidence showing SPC to be significantly more bioavailable than uncomplexed silibinin and document bioavailability in both cats and dogs.[2-4]

Provision of standardized veterinary milk thistle products, with evidence based pharmacokinetic and therapeutic recommendations, is particularly important when approaching the common misconception that milk thistle products are not useful to the veterinary practitioner due to low bioavailability. As illustrated in Figure 1, studies have shown that complexing silybin into a phytosome with phosphatidylcholine not only dramatically increases the bioavailability as evidenced by the Cmax and AUC, but also allows it to enter into the bloodstream more rapidly, as evidenced by the Tmax of SPC as compared to silymarin extract.[4]

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Figure 1. Comparison of key pharmacokinetic parameters in plasma of silymarin extract and silybin: phosphatidylcholine complex (SPC) in Beagles, administered equivalent amounts of silybin with *p < .05. A: Maximum plasma concentration (Cmax); B: 24-hour area under the curve (AUC); C: Time to maximum concentration (Tmax).

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In other studies evaluating the bioavailability of Marin, the plasma concentrations of silybin in dogs given SPC were 3–4.4 times greater than those in dogs given another oral silymarin extract, as illustrated in the Figure 2.[3] This study was also important in establishing Marin's safety profile in dogs, which has not been documented with other SPC products.

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Figure 2. Silybin plasma concentration time course after dosing with silybin-phosphatidylcholine complex (SPC) or silymarin extract. Values represent the mean values ± standard deviation of measured levels after subtraction of background peaks averaged for days −1 and 0.

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Beyond demonstrated efficacy and safety, Marin contains additional elements that support overall liver health beyond that of SPC, namely vitamin E and zinc. The authors acknowledge a discussion of the benefits of milk thistle extracts in domestic animals with liver disease is incomplete without the specific mention of the commercially available product Marin and corresponding scientific evidence for its use.

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