Prescribing errors in patients with documented drug allergies: comparison of ICD-10 coding and written patient notes

Introduction: Allergies to drugs are a major cause for hospitalisation and inappropriate prescriptions to patients. However, allergies can be prevented if the patient’s history of drug allergy is known and coded. Objective of the study: Assessment of the value of the widely used ICD-10 codes for drug-allergies (e.g. Z88, L27) as triggers for decision support in an electronic prescription system and evaluation of the potential impact of such an alert system. We also evaluated the usefulness of manual drug allergy notes recorded in patients’ charts in the prevention of prescribing errors due to drug allergies. Setting: University hospital providing primary and tertiary care. Methods: Using Anatomical Therapeutic Chemical (ATC) classification codes we allocated to drug specifying ICD-10 codes (i.e. Z88) all drugs belonging to the same group of compounds or those known to induce cross-allergy. In a randomly selected cohort of 200 in-patients we then assessed documentation and coding of drug allergies and incident prescribing errors ignoring patients’ drug allergies. Results: Eighteen of the 200 patients had an allergy-related ICD code in the chart, 51 had a written note, and 13 had both. About 21% of patients with documented drug allergies were prescribed a drug potentially triggering the allergy. There was no difference in prescribing errors due to drugs potentially inducing allergies when the allergy was only documented as an ICD-10 code or the information was available in the paper record (P > 0.05). Conclusion: The findings of this study emphasise the necessity of a more precise and efficient documentation system of drug allergies along with the implementation of an electronic CDS for drug allergies that makes physicians aware of patients’ drug allergies during the prescribing process.