Measurement of aspirin and paracetamol metabolites.

Clinical laboratories are frequently asked to measure the concentration of drugs in blood and urine. Of the many thousands of drugs prescribed, however, the measurement of only a relatively small number provides useful clinical information. There are three main reasons for measuring drugs: to test patient compliance, to ensure that dosage is high enough to have therapeutic effect but sufficiently low to avoid toxicity and, finally, to identify drugs taken during deliberate or accidental overdose. This article is concerned with the last of these.