ABSTRACT
Adverse drug reactions account for about 2% of acute hospital admissions and occur in 10-20% of hospital inpatients. A patient with diabetes and associated cardiovascular disease is likely to be taking more than 10 drugs, all of proven efficacy. The greater the number of drugs that a patient receives, the greater the risk of drug interactions. In a large study in north-west England, involving almost 20,000 patients admitted to hospital, this was by far the most important type of interaction. Interactions at the site of action can be additive or antagonistic. As with adverse effects, most interactions occur with drugs at their site of action or because the routes of elimination are affected. Interactions become important when the dose of a drug is critical and a small change in the amount of drug in the body results in toxicity or lack of therapeutic effect.
