IdB 1016 is a complex of silybin (the main active component of silymarin) and phosphatidylcholine, which in animal models shows greater oral bioavailability and therefore greater pharmacological activity compared with pure silybin and silymarin. In order to assess its pharmacokinetic profile in man, plasma silybin levels were determined after administration of single oral doses of IdB 1016 and silymarin (equivalent to 360 mg silybin) to 9 healthy volunteers. Although absorption was rapid with both preparations, the bioavailability of IdB 1016 was much greater than that of silymarin, as indicated by higher plasma silybin levels at all sampling times after intake of the complex. Regardless of the preparation used, the terminal half-life was relatively short (generally less than 4 h). In a subsequent study, 9 healthy volunteers received IdB 1016 (120 mg b.i.d., expressed as silybin equivalents) for 8 consecutive days. The plasma silybin level profiles and kinetic parameters on day 1 were similar to those determined on day 8. Most of the silybin present in the systemic circulation was in conjugated form. Less than 3% of the administered dose was accounted for by urinary recovery of free plus conjugated silybin, a significant proportion of the dose probably being excreted in the bile. It is concluded that complexation with phosphatidylcholine in IdB 1016 greatly increases the oral bioavailability of silybin, probably by facilitating its passage across the gastrointestinal mucosa.

The most important part of a medicine as far as its weight is concerned, is constituted by its excipients, which have the important functions of guaranteeing the dosage, stability and bioavailability of the active principle. The components employed as excipients must present the characteristics required by their technological function but, as with any substance administered to man, they must also correspond to suitable safety requirements. In fact, in the past the importance of evaluating the possible adverse effects of excipients was underestimated, because their inertia and innocuity were taken for granted. The safety profile of these substances is more deeply researched as regards the toxicological aspect only if they are also employed in the food industry (anti-oxidants, sweeteners, colouring agents, etc.). Indeed, in this case, the International Toxicological Committees (among which the Joint Expert Committee on Food Additives, a mixed committee of the WHO/FAO) demand thorough studies in laboratory animals, with the intent of protecting the consumer's safety. Tackling the question of the toxicity of excipients thoroughly is not a simple matter for several reasons: the large number of substances on the market and the diversity of their chemical profiles, their sources, their technological functions, and the presence of secondary products and/or contaminants that may be the true causes of adverse effects. In this article we shall review the principal classes of excipients and their respective side effects. Then we shall proceed to their toxicological evaluation, giving examples of: (a) intrinsic toxicity, or adverse effects that may be encountered in the whole population; and (b) specific toxicity, which manifests only in people who are carriers of a transmissible disease or who are genetically predisposed, such as people with allergies and intolerances.

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The plasma level profile and the biliary excretion of silybin, the main flavanolignan component of silymarin, were evaluated in rats after single equimolar oral doses (200 mg/kg, expressed as silybin equivalents) of the silybin-phosphatidylcholine complex silipide (laboratory code IdB 1016) and of silymarin. Silybin was assayed by using a specific HPLC method which allowed also the determination of other flavanolignans present in the biological fluids after administration of silymarin (i.e. silydianin, silycristin and isosilybin). After oral silipide, silybin reached peak plasma levels within 2 h, with a Cmax of 9.0 +/- 3.0 micrograms/ml for unconjugated drug and 93.4 +/- 16.7 micrograms/ml for total (free + unconjugated drug). Maximum total biliary concentrations of silybin (2989 +/- 568 micrograms/ml) were observed within 2 h and the biliary recovery after 24 h accounted for about 13% of the administered amount. After administration of silymarin, unconjugated and total plasma silybin levels as well as biliary excretion were several-fold lower than those observed after treatment with silipide. Silybin recovered over a 24 h period after silymarin intake accounted for about 2% of the administered dose. Plasma and bile obtained after administration of silymarin contained also silydianin, silycristin and, to a greater extent, isosilybin. The concentrations of the latter compound in plasma and in bile were higher than those of silybin itself. The relative bioavailability of silipide (calculated in the target organ as the ratio between AUCs of cumulative biliary excretion curves) was 10-fold higher than that of silymarin.

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