Drug

I

Introduction

Drug, chemical or other substance that alters the function of an organism. Such chemicals are used for the prevention, treatment, and alleviation of disease. The term “medicine” (such as in prescription-only medicine) is sometimes used to distinguish therapeutic drugs from recreational and other drugs, such as opiates, which are used illegally. This article covers therapeutic drugs—for information about other drugs, see Drug Dependence. The study of action of drugs in the human body is called pharmacology.

The use of drugs dates from prehistoric times; the first list of drugs with instructions for preparation, called a pharmacopoeia, appeared in 1546 in Nuremberg, Germany. Drugs can be derived from plant, mineral, animal, or synthetic sources. Many early folk medicines, including aspirin, digitalis, ergot, opium, and quinine, were derived from plants. Minerals used as medicines include boric acid, Epsom salts, and iodine. Many hormones used to treat a bodily malfunction—such as insulin for diabetes, or growth hormone to promote proper human development—may be obtained from animals. Some newer analgesic (pain-killing), sedative, psychoactive, and anaesthetic drugs have been developed entirely by chemical analysis, and many substances formerly obtained from animals, plants, or other organisms are now made synthetically. Some of the newest drugs are produced by biotechnology or genetic engineering.

II

Administration of Drugs

A drug may be administered by mouth (orally) or through the skin (parenterally). Parenteral methods include: injection into a vein (intravenously); into a muscle (intramuscularly); under the skin (subcutaneously); in a patch or as a cream or lotion on to the skin (topically); as a nasal spray (intranasally); or as a suppository (rectally). Intravenous administration may entail injection using a hypodermic needle, or a continuous flow through a cannula, which has been inserted and left in a vein. Oral drugs can be formulated to dissolve slowly in the stomach or gut in slow-release or controlled-release versions. Drugs for asthma are often made in an aerosol form for spraying down the throat into the lungs. The insulin pump, a small battery-driven instrument strapped to the body, delivers insulin continuously into the blood of a diabetic to imitate the natural release of insulin from the pancreas of someone who is not diabetic. One form of intramuscular injection is the depot preparation in which the drug is formulated to be released slowly via the tissues into the blood capillaries. Some insulins, steroids, and contraceptives are given in this way.

III

Use of Drugs

An important consideration in drug therapy is the risk-to-benefit ratio of the drug; that is, measuring its benefits against risks of proven side-effects. For example, the antibiotic gentamicin, a derivative of streptomycin, can damage the kidneys, so there must be regular careful medical supervision when large doses are required. The drug ganciclovir is used to treat life-threatening or sight-threatening cytomegalovirus infections, but because it can cause cancer, regular clinical and haematological assessments (blood tests) are recommended.

An aid to the effective use of many drugs is the determination of the amount of the drug in the blood; this is called serum monitoring. For some drugs used to treat epilepsy, for example, the difference between a therapeutic and a toxic drug concentration is small, so the exact blood level needs to be known. Use of the anticoagulant heparin also requires precise adjustment of the dose by serum monitoring.

When doctors are considering which drug to prescribe, they need to consider the contraindications; that is, medical conditions where the drug should not be given, or where there is hypersensitivity to that drug. If the patient is pregnant, the doctor must consider whether the drug could be passed to the foetus. The doctor must also find out what other drugs the patient may be taking, including over-the-counter drugs. This is because many drugs have adverse side-effects through interactions with other drugs, foods or alchohol, as well as when taken on their own. Such interactions may also simply negate the effectiveness of a drug. The patient also needs to be forewarned of any possible side-effects and be told about any special precautions and storage requirements (some drugs have to be kept refrigerated). All drugs have to be accompanied by a patient information leaflet which contains this and other useful information.

IV

Research and Testing

In the wake of the development of the sulpha drugs (see Sulphonamides) in the 1930s and penicillin in the 1940s, the pharmaceutical industry became geared to intensive research on antibiotics, antihistamines, steroid hormones, and many other kinds of drugs. Discovery of a new drug triggers an elaborate programme to test toxicity, first on small animals such as rats or rabbits, then on larger animals such as dogs or monkeys. In most countries approval must be obtained from the appropriate government body for clinical trials on humans. The first trial, Phase 1, uses a few healthy volunteers to test for toxicity, tolerance, absorption, and excretion. Phase 2 tests the drug on a small number of patients suffering from the illness the drug is intended to combat. If the drug has safely passed these trials and has proved to be an effective treatment, Phase 3 tests it in comparison with a placebo (inert substance), on hundreds of volunteers in a blinded trial. In such a trial, patients do not know if they are being given the active drug or the placebo. Only if the drug shows measurable benefit will an application be made to license it.