How to Choose the Ideal Venotonic or Vasoprotective – Which Properties Are Key?
Medicines and dietary supplements containing flavonoids, often hesperidin or diosmin, are available on the market. What should you consider when choosing these products?
Effects of Flavonoids on Blood Vessels
Natural substances from the flavonoid glycosides group have a number of beneficial pharmacological effects confirmed by both preclinical and clinical research. Hesperidin, diosmin, and some other related flavonoids are used as venotonics and vasoprotectives to treat symptoms and manifestations of chronic venous insufficiency of the lower limbs or during acute manifestations of hemorrhoids. The action of diosmin is a combination of the following effects:
- reduction of venous distensibility and venostasis
- normalization of capillary permeability and increase of capillary resistance
- increase of lymphatic flow
Diosmin and Diosmetin
Citrus fruits, used in pharmaceutical purposes, have a high content of venotonic flavonoids. Hesperidin is extracted from their pericarp. It is then purposefully converted to diosmin by dehydrogenation. However, the reaction also leads to other products, and the resulting mixture is referred to as the so-called flavonoid fraction. The aim is to obtain a mixture with a predominance of diosmin.
In the body, the sugar component is hydrolyzed off from these flavonoids, and the so-called aglycone is formed. The aglycone of hesperidin is called hesperetin, from diosmin arises diosmetin. These two aglycones — the actual active substances — are significantly different in terms of pharmacokinetics; diosmetin has a multiple times longer biological half-life than hesperetin, amounting to 26–43 hours.
Hesperidin as an Impurity in Diosmin
The above-mentioned flavonoid fraction with a relatively large representation of hesperidin and other flavonoids is usually used in medicinal products and dietary supplements. From a therapeutic perspective, however, it is more advantageous to administer the purest possible diosmin. A 100% pure substance exists only for laboratory purposes. For the manufacture of medicines, the European Pharmacopoeia sets permissible impurities and their content. These include the following flavonoid glycosides:
- hesperidin (max. 4%)
- isorhoifolin (max. 3%)
- linarin (max. 3%)
There are several diosmin products on the market, and it is easy to verify how pure the active substance is. If the impurities are present in under-limit amounts, they don’t have to be listed in the Summary of Product Characteristics (SPC). Such a product will then list only diosmin as the active ingredient, and not hesperidin or flavonoid fraction.
Improving Bioavailability
Another characteristic that an ideal flavonoid-containing product should have is micronization of the drug, which ensures optimal absorption of diosmin when taken orally. This process reduces the size of the drug particles to micrometers, increasing the active surface area and improving solubility. Diosmin is practically insoluble in water; for similar poorly soluble substances, the aim is to achieve particle sizes of up to 10 μm — at these dimensions, active transport systems can already be involved in the absorption in the body. This achieves not only faster release of the active substance but also higher plasma concentrations of the drug.
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Sources:
1. Okáčová L., Vetchý O., Franc A. et al. Increasing the availability of poorly soluble substances by their modification. Chemické listy 2010; 104: 21–26.
2. Diozen — diosminum micronisatum. Brochure for professionals. Zentiva.
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