drug

drug The term ‘drug’ has become something of a misnomer. Strictly, a drug is a chemical substance used to treat disease in animals, including man. Today, a drug is a pure chemical substance whose structure is known and is formulated, by mixing it with other materials, into a preparation suitable for administration. This results in the familiar tablets, pills, injections, liquid mixtures, emulsions, and syrups; ointments, creams, and salves; infusions and tinctures; drops for eyes, ears, and noses; sprays for inhalation, gases delivered by machine, supositories, and the like. In earlier times drugs were not always pure, single substances, but mixtures of substances together with many unknown constituents, and were derived from medicinal plants. Here the dried leaves, roots, stems, bark, or rhizomes of plants were ground into powders or used to prepare infusions, tinctures, syrups etc. For example, malaria was treated with infusions made from cinchona bark, and constipation by extracts of casacara sagrada bark. Today, the same diseases might be treated with tablets containing quinine or emodins, respectively.

Approved drugs are those which have passed all the stringent tests for safety and efficacy granted by organizations such as the Committee on the Safety of Drugs (in the UK) and the Federal Drugs Administration (FDA) (in the US). Approved drugs then become listed in National Formularies and pharmacopoeias of various countries. The designation BP, USP, or EP after the name of a drug implies it conforms to the standards described in the British, US, or European Pharmacopoeias. Even crude drugs, made from medicinal plants, were standardized during preparation to give galenicals having the same potency from batch to batch and as given in the pharmacopoeias.

With the advances in science and medicine it became appropriate to extract and purify drugs of plant origin, separating them from other plant constituents so that they could be formulated as with pure drugs. As the chemical structures of drugs were discovered it became clear that it could be economically sound to synthesize the compound chemically, rather than to rely on its synthesis by plants, together with all the attendant problems of extraction and purification. The commonly-held view that drugs produced naturally are good while synthetics are bad is a myth. The same substance produced by nature or by chemical synthesis is identical in its actions. The idea of vital force, believed to be locked away in molecules of natural origin, was destroyed in 1828 when Wohler produced the naturally-occuring substance urea from inorganic starting materials.

Open any newspaper or listen to any news broadcast and you are likely to read or hear about drugs — drug problems, drug abuse, drug culture, drug barons, drug smuggling. While it is true that Harry Lime smuggled penicillin in the Third Man, the film portraying racketeering in post World War II Europe, today's references refer almost exclusively to drugs of abuse which lead to addiction. It is entirely possible for a drug to be a useful therapeutic agent as well as a drug of abuse. Properly used, morphine and its derivative heroin are excellent analgesics, which can be used without causing addiction. In former times cocaine was the local anaesthetic used by most dentists, and currently cannabinoids (from marajhuana) are being examined for their usefulness in multiple sclerosis.

Chemical modification of a drug can be made without necessarily affecting either its biological effects or its potency. In this way a new substance is produced which is not covered by any legislation. So-called designer drugs produced from drugs used for their abuse potential thus enter the illicit marketplace. In these situations rapid actions are necessary to prevent the rapid spread of their use.

The potential of chemical substances to modify biological function in disease states is still a largely untapped area. The appearance of new diseases (e.g. HIV, BSE) creates urgent demands for drug discovery. The cloning of the human genome, and identification of genes and their functions, combined with high throughput screening methods and combinatorial chemistry, will lead to a revolution in drug discovery programmes. The control of drug abuse is likely to be a more intractable problem.

Alan W. Cuthbert

See also addiction; drug abuse; drug administration.