Herbal medicine: Dry extracts production and applications

Abstract

Medicinal plants have provided therapeutic agents for thousands of years and continue being a great source of novel pharmaceutical products. Two-thirds of the world population still relies to some extent on natural medicines for primary health care. In addition, the demand for medicinal plant products is now increasing in both developing and developed countries as a consequence of a growing aging population and increasing consumer awareness about general health. Nevertheless, there is a widespread concern regarding safety, efficacy and quality of herbal medicines. Currently, many countries are conscious about the need of regulatory guidelines for medicinal herbs formulation, production and use. Phytomedicines represent a wide range of product types: from raw herbs (dried or fresh) to others with different processing degrees (such as tinctures and extracts). The production of herbal medicines involves adequate cultivation and post-harvest methodologies as well as botanical identification of the vegetable drugs. For herbal medicine end-products with added value, appropriate extraction procedures (i.e., in terms of bioactivity), standardization of extracts, selection and tuning of the drying processes operating conditions and design of pharmaceutical formulations are also necessary. In this chapter the current global scenario of phytomedicine is first presented, evaluating its impact on public health and markets. The challenges associated to safety, efficacy and quality of herbal medicines due to the extracts complexity are then introduced. Understanding the great importance of providing accurate dosages of herbal therapeutic agents, the production of dry plant extracts is next discussed focusing on: the drying step including the formulation of the solution to be dried (which comprises the herbal extract) and the dried extract quality. Regarding the available technologies for preparing dry medicinal plants extracts, spray drying is particularly described. This technique is the most commonly used in the herbal processing industry due to its ability to generate particulate products with precise specifications in continuous operations. Several key studies about the effect of the operating conditions and feed composition on the yield of the spray drying process and the particles properties are subsequently summarized. For the production of tablets by direct compression, stable herbal dried powders with good flow properties are required. Consequently, the effects of different processing variables on the stability and flowability of dried extracts are also presented. The formulation of solid dosage forms, based on spray-dried plant extracts, for conventional and modulated delivery is then reviewed. Besides, existing strategies to modulate the drug delivery of plant extracts are also described. Since modified-release phytomedicines are still in an exploratory stage, the prospective for the development of novel products is finally discussed.