Drug level monitoring in paediatric practice

Abstract

A knowledge of the concentration of a drug in blood or other tissue fluid is now considered an important and sometimes essential part of the therapeutic management of various conditions. Its importance has increased as information showing wide interindividual variation in drug response has become recognised. Such variation arising from differences in absorption, distribution, and elimination appears to be greater during development, and yet many drugs are still prescribed for children in doses calculated by scaling down adult doses according to weight or surface area. For many drugs, there is a close relationship between plasma level and therapeutic effect, and the value of knowing the plasma level has been proved for a number of drugs. Although fewer data are available for these drugs in children, in the case of most drugs the plasma level-therapeutic response relationship will be better than that between dosage and clinical effectiveness. However, it should be remembered that the clinical effects of some drugs cannot be adequately monitored by concentration measurements, as in the case of cytotoxic agents where there is no temporal relationship between drug level and effect.