Читать книгу Clinical Pharmacology and Therapeutics - Группа авторов - Страница 162

When administration of one drug influences the effect of another, the term ‘drug interaction’ is used. Interactions account for approximately one quarter of all adverse drug reactions, and are most commonly seen in elderly people taking a variety of drugs for multiple problems. There are an almost limitless number of drug interactions and while it is important to be aware of some of the most commonly encountered ones, there is no substitute for looking up prescribing resources or consulting a pharmacist. This is particularly important when prescribing an unfamiliar drug.

Drug interactions can result from interference between the pharmacological action of the drug – for example through action on the same receptor or a similar biological process – or it may be due to interference with drug absorption, metabolism or clearance leading to altered drug levels at the site of action. It is important to bear in mind that drug interactions can also occur between non‐prescribed drugs such as over the counter medicines or herbal remedies. St John's Wart can be bought in health food shops and is known to interfere with the metabolism of many drugs. Grapefruit juice is also known to alter the bioavailability of many drugs.