Random and systematic medication errors in routine clinical practice: a multicentre study of infusions, using acetylcysteine as an example

Aims The nature and incidence of errors in prescribing and giving medicines have previously been estimated by trained observers, or by retrospective a nalysis of incidents in which patients have come to harm. We have examined prospectively in routine clinical practice the concentrations of intravenou s infusions of a drug (acetylcysteine) which is given according to a compli cated dosing schedule. Methods We prospectively collected samples before and, where possible, afte r the infusion of acetylcysteine in 66 anonymous patients requiring treatme nt for acetaminophen (paracetamol) overdose in four centres in the United K ingdom. We measured the concentration in each infusion bag, and deduced fro m the weight of the patient the percentage of the anticipated dose that had actually been given. Results The experimentally determined dose was within 10% of the anticipate d dose in 68 of 184 individual bags (37%), and within 20% of the anticipate d dose in 112 bags (61%). Doses in 17 bags were more than 50% from the anti cipated doses. In three patients, values in all three bags appeared to be s ystematically wrong by 50% or more; in a further seven cases, individual ba gs differed by 50% or more from the anticipated value. The median differenc e between pre- and post-infusion samples was 0% [interquartile range -5.2% to +14.6%], but 9% showed a disparity of greater than +/- 50%. Conclusions Our data suggest that there is large random variation in admini stered dosage of intravenous infusions. Systematic calculation errors occur ill about 5% [95% confidence interval 2, 8%] of cases, and major errors in drawing up in a further 3% [1, 7%], with inadequate mixing in 9% [4, 14%]. While we have no evidence that patients were adversely affected, and while the regime of administration of the drug studied (acetylcysteine) is compl icated, these data suggest that the delivered dose often deviates from the intended dose, and that methods of quality control are needed.