Superior bioavailability is also an under-researched advantage of herbal liquids. When a solid dosage preparation is ingested, it must first disintegrate. The plant’s phytochemicals need to dissolve in digestive juices (and the water simultaneously imbibed with the tablet or capsule) to be absorbed by the body. Research has demonstrated that there is a relationship between the rate and degree of dissolution of the phytochemicals in a solid dosage preparation and their ultimate absorption into the bloodstream. The advantage of herbal liquids is that the all-important phytochemical constituents are already in solution.
The main disadvantage of liquids is taste, although in the case of bitters the taste is an essential part of the therapy. The taste problem is somewhat exaggerated by some patients. Most patients get used to the taste of their mixture, and some even grow to like it. If taste becomes a problem, there are flavoring preparations available, and these are particularly useful for children.
Sometimes the best way to prescribe an herb is as a powder. This mainly applies to mucilage-containing herbs. When these herbs are mixed with water, the mucilage reacts with the water to form a gel, and the wet herb swells to many times its original volume. Mucilage is not very soluble in alcohol-water mixtures; hence it is difficult to use mucilaginous herbs effectively as liquids. In any case, if fluid extracts of, say, slippery elm and marshmallow were made correctly, they would be so gelatinous that they could not be poured.
When giving mucilaginous herbs as powders, it is best to advise the patient to mix them quickly with water and to take the mixture immediately before it swells. Otherwise, the patient often experiences difficulty negotiating the gelatinous mass which results. A copious amount of water should then be consumed to allow swelling in the stomach. Other herbs given as powders are also best taken slurried with water and rinsed down with additional water.
Tannin-containing herbs for the treatment of colon problems should also be given as powders. This is because the tannins are only slowly dissolved from the herb matrix and, therefore, are still being released in an active form when the powdered herb reaches the colon.
A big advantage of powders is that the total constituents of an herb are presented to the patient’s digestive tract, rather than those constituents which only dissolve in alcohol or water. This can also be a disadvantage if the patient has compromised digestion. Where the fat-soluble components are an important part of the activity of an herb, the powder should be followed by a dose of vegetable oil or lecithin to assist absorption.
Herbal tablets are a convenient dosage form, and no problems with taste or alcohol are associated with their use. However, tablets contain fixed formulations which cannot be precisely adapted to the needs of the individual patient. Therefore, it is critical that the herbs listed in a tablet are carefully chosen for the disorder they are intended to treat. Even then, the degree of treatment flexibility is limited.
A major potential problem with tablets is the degree of processing required. Processing is minimal for tablets containing the powdered herb, but the amount of herb which can be incorporated into such tablets is limited (without making them excessively large). Tablets are therefore usually made from extracts, which are more concentrated than the original dried herb. In order to achieve this, the herb is first extracted with a solvent. Often water is used to keep costs down. The resultant liquid is then dried to either a soft or a powdered concentrate using processes such as vacuum concentration or spray drying. Heat-sensitive or volatile components can be damaged or lost by this process. Heat is also sometimes used in the tablet-making process via a granulation step: the tablet mixture may be wetted and then dried in an oven before the final pressing. This risk further damage to the active components. Hence, when manufacturing tablets, quality may be sacrificed for the sake of quantity.
INFUSIONS AND DECOCTIONS
Infusions and decoctions are time-honored methods for delivering oral doses of herbs. In modern phytotherapy, they are mainly used where the active components of the herb are water soluble, for example, for herbs containing polysaccharides, tannins or mucilage or some glycosides. They also can be advantageous for the treatment of urinary tract problems and the administration of alterative (depurative) herbs. Diaphoretics should be given hot to maximize their effectiveness; hence they are often administered as infusions or decoctions.
The major disadvantage of infusions or decoctions is that water is not a good solvent for many of the active components in herbs. This problem is compounded by the relatively short extraction time used in their preparation (usually 5 to 10 minutes). In addition, the large volume of hot liquid usually means that exposure to any unpleasant taste is considerably prolonged. The higher doses of herb often used in infusions and decoctions can sometimes compensate for the limitations of hot water as a solvent.
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