The hazards of prescribing from serum levels

Clinical audit at a mental handicap hospital suggested that doses of antiepileptic drugs were being altered in response to suspiciously high or low serum level results. In order to assess the reliability of such results, sequential serum levels for individual patients were examined for consistency. Correlation between results which should have been the same was found to be so low as to call into question the value of drug serum level sampling in this hospital. Investigation of the source of the variability continues. In the meantime, clinical staff are reminded that it is unsafe to make any decision on the basis of a single drug serum level.