Drugs that block pain sensations in a limited region of the body
Local anaesthetics produce reversible loss of sensation in a specific area of the body. They have a wide range of uses, including the prevention of pain during minor surgical procedures or diagnostic tests. The drugs are also used to produce regional anaesthesia, sometimes called a nerve block, in which a large area of the body is anaesthetized. Local anaesthetics vary in potency and in the duration of their effect. They work by temporarily preventing the conduction of pain signals along nerve fibres.
A local anaesthetic may be injected directly into the site at which sensation needs to be blocked (see Having a local anaesthetic). For example, local anaesthesia may be used to numb a small area of skin before the removal of a mole. Local anaesthetics may also be applied to the skin or the mucous membranes as a cream, gel, or spray. Some products that contain a local anaesthetic are available over the counter; these include throat lozenges and suppositories or ointments used to relieve painful haemorrhoids.
Regional anaesthesia is used to anaesthetize a large area of the body. The drug is usually injected at a site close to a nerve or bundle of nerves that supplies a specific area of the body (see Having a regional anaesthetic). The anaesthetic then numbs the entire area supplied by that nerve or nerve bundle. One example of this type of anaesthesia is epidural anaesthesia, in which a local anaesthetic is injected into the space around the spinal cord. This procedure anaesthetizes the whole of the lower body and is sometimes used as a form of pain relief during labour (see Epidural anaesthesia in labour).
Some local anaesthetics applied to the skin can cause an allergic reaction if they are used repeatedly. If a large dose of local anaesthetic becomes absorbed into the bloodstream, it may lead to symptoms such as dizziness.
Following an epidural anaesthetic, you may have a headache or backache that can last for several days.
From the 2010 revision of the Complete Home Medical Guide © Dorling Kindersley Limited.