4. Mode of administration

The active ingredients of chemical medicines are usually relatively simple molecules. Advances with medicines formulations made it possible that many can be taken orally as tablets or liquids, applied as creams, lotions, eye drops, nasal sprays (topical) or patches on the skin (transdermal) which means that patients can take them at home. For example, eye infections are often treated with a topical eye-drop formulation of an antibiotic, rather than with a tablet, to allow the medicine to act where it is most effective. Some chemical agents, however, must be injected under the skin (subcutaneous), into a muscle (intramuscular) or directly into the blood stream (intravenous). The different ways of administering medicines can help to ensure the medication is delivered at the right speed. Some medicines need to act very quickly, such as salbutamol in the case of an asthma attack which is inhaled. Other medicines should work slowly and over several hours. Medicines such as growth hormone can be injected into the fat under the skin because there are few blood vessels there and the medication can take up to 24 hours to find its way into the bloodstream to reach the target.