Drug eruptions.

The last four decades have seen an enormous increase in the use of potent and toxic drugs as therapy. The considerable advances that these drugs have provided in the control and prevention of disease are matched by their potential to produce unwanted side effects many of which are reflected in the skin. These side effects cannot in the main be predicted. Tests in animals may not reliably be extrapolated to the human and only occasionally can the occurrence of side effects be gauged from the structural formula of a new drug. With some fifty new drugs developed each year the practitioner is challenged simply to keep pace with their therapeutic indications. The results of one survey suggested that 30% of prescriptions from general practitioners was based on data supplied by drug companies. In 1985 it is also increasingly common to find that patients, when faced with a chronic disease have sought several medical opinions or have taken refuge in remedies which rely more on advertising than their therapeutic effectiveness. The available information suggests then that drug reactions are likely to be common. In a recent study (Black & Somers, 1984), drugrelated illness accounted for some 6% of hospital admissions in a year. It has been estimated that the average inpatient in a British hospital receives five drugs whilst one in an American hospital receives nine. Since a large majority of allergic reactions affect the skin the incidence of drug-induced cutaneous eruptions probably reflects the risk of allergic drug reactions in general. Reactions to drugs in over twenty thousand medical inpatients were studied in a large collaborative study (Arndt & Jick, 1976). Skin reactions occurred in a little over 2%. Despite the lack of data on non-hospitalized patients it is clear that even if only 2% of patients receiving drugs experience a 'rash' it is a number that we can all ill afford. Mechanisms of adverse drug reactions