Chapter 1 Importance of plants in modern pharmacy and medicine
Types of drugs derived from plants
Herbal drugs derived from specific parts of a medicinal plant
Botanical drugs which form the basis for herbal remedies or phytomedicines include, for example:
• the herb of St John’s wort (Hypericum perforatum), used in the treatment of mild to moderate depression
• the leaves of Ginkgo biloba, used for cognitive deficiencies (often in the elderly), including impairment of memory and affective symptoms such as anxiety
• the flower heads of chamomile (Chamomilla recutita), used for mild gastrointestinal complaints and as an anti-inflammatory agent
• the leaves and pods of senna (Cassia spp.), used for constipation.
Natural products or compounds isolated from nature
• morphine, from opium poppy (Papaver somniferum), used as an analgesic
• digoxin and other digitalis glycosides, from foxglove (Digitalis spp.), used to treat heart failure
• taxol, from the Pacific yew (Taxus brevifolia), used as an anticancer treatment
• quinine, from Cinchona bark (Cinchona spp.), used in the treatment of malaria
• galanthamine from Galanthus and Leucojum species, used in the management of cognitive disorders.
Use of herbal medicines
The use of these remedies is extensive, increasing and complex. In several surveys 20–33% of the UK population claimed to regularly use CAM alone or in addition to orthodox or conventional medicine and treatments. In the UK, usage is particularly frequent amongst those who are over-the-counter medicines-users. There is not, on the whole, a wide understanding of what herbal medicines are (or are not) (IPSOS-MORI 2008). Healthcare professionals and students also commonly use such products. Forty-three percent of students at a University School of Pharmacy reported using at least one type of CAM during the last 12 months (Freymann et al 2006).
In the United States, approximately 38% of adults and approximately 12% of children are using some form of CAM (NIH/NCCAM). Kennedy et al (2008) showed that in the preceding 12 months about 38 million adults in the US (18.9% of the population) used herbal medicines or supplements, but that only one-third revealed this use to their physician. Data for other regions are even more limited, but the usage of herbal medicines is widespread in countries like India, Indonesia, Australia and China, to name just a few.
In developed countries, most purchases of HMPs are made on a self-selection basis from pharmacies and health-food stores, as well as from supermarkets, by mail order and via the Internet. Normally, with the exception of pharmacists, there is no requirement for a trained healthcare professional to be available on the premises to provide information and advice. In any case, most HMPs can be sold or supplied without the involvement of a healthcare professional and several studies have confirmed that many individuals do not seek professional advice before purchasing or using such products, even when purchased from a pharmacy (Barnes et al 1998, Gulian et al 2002). Rather, consumers of HMPs tend to rely on their own (usually limited) knowledge, or are guided by advice from friends and relatives or the popular media. Consumers who do seek professional advice (e.g. from their pharmacist or general practitioner) may find that he or she is not able to answer their question(s) fully. In some cases this may be because the information simply is not available, but it is also recognized that, at present, many healthcare professionals are not adequately informed about herbal medicines, particularly with regard to their quality, safety and efficacy. This book attempts to redress that omission.
HMPs are used for general health maintenance, as well as for treating diseases, including serious conditions such as cancer, HIV/AIDS, multiple sclerosis, asthma, rheumatoid arthritis and osteoarthritis. Older patients, pregnant and breastfeeding women, and children also take HMPs, and this raises concerns because, as with conventional medicines, precautions need to be taken. For example, few medicines (whether conventional or herbal) have been established as safe for use during pregnancy and it is generally accepted that no medicine should be taken during pregnancy unless the benefit to the mother or fetus outweighs any possible risk to the fetus. Similarly, HMPs should be used with caution in children and the elderly, who, as with conventional medicines, differ from adults in their response to, and metabolism and clearance of drugs. The use of herbal medicines by patients who are already taking prescribed medicines is of particular concern as there is the potential for drug–herb interactions to occur. For example, important pharmacokinetic and pharmacodynamic interactions between St John’s wort (Hypericum perforatum) and certain conventional medicines have been documented (Williamson et al 2009) and mechanisms for such interactions have been identified. Generally, information on interactions between HMPs and conventional medicines is limited, although potential drug–herb interactions can sometimes be identified based on the known phytochemistry and pharmacological properties of the herbs involved.
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