Objective To monitor unprevented dispensing incidents in NHS hospitals by identifying incident types, drugs involved and factors that may have contributed to the occurrence of incidents. Setting All 20 Welsh NHS hospitals (15 district general; 2 teaching; 2 psychiatric and 1 other specialist hospital). Method Unprevented dispensing incidents that occurred between January 2003 and December 2004 were reported and analysed using a validated method. Incident rate was calculated for those hospitals that provided both incident and issue data. Incident rate was compared with previous research using a two‐sample t‐test. Reported incident types and contributory factors were compared with previous research using chi‐square analysis. Key findings A total of 1005 unprevented dispensing incidents were reported by 20 hospitals. The overall incident rate, based on data from 17 hospitals, was 16 incidents per 100000 items dispensed (range 0.2–46 incidents per 100000 items dispensed). The overall dispensing incident rate was less than previously reported (18 incidents per 100000 items dispensed).This finding was not statistically significant (t = 0.421, P = 0.676). The most common incidents reported were dispensing the wrong strength of drug (n = 241, 24%), wrong drug (n = 168, 17%), wrong form (n = 134, 13%) and printing the wrong warnings/directions on the label (n = 112, 11%). A statistically significant finding was that fewer incidents involving dispensing the wrong drug were reported by Welsh hospitals (17%) compared to previous research in the UK (23%; P = 0.01). Drugs most commonly involved in incidents were insulin (n = 34; 6 incidents per 10000 issues of insulin), nifedipine (n = 16; 10 incidents per 10000 issues of nifedipine) and carbamazepine (n = 10; 5 incidents per 10000 issues of carbamazepine). Conclusion The overall unprevented dispensing incident rate was less than previously reported. Dispensing the wrong strength of the correct drug is a problem. Staff should be aware of the risk of dispensing incidents involving insulin, nifedipine and carbamazepine. Strategies for minimising dispensing incidents include using shelf labels to highlight different strengths or formulations of the same drug, and educating staff about easily confused drugs.

Focal points

The use of prevented dispensing incidents as a surrogate marker for unprevented incidents is questionable. There were significant differences between unprevented and prevented dispensing incidents in terms of rate and error types. This is consistent with the medication error iceberg. Care must be exercised when extrapolating prevented dispensing incident data on error types to unprevented dispensing incidents.