Antimicrobial Residual Drug Error in the Intensive Care Unit; a Single Blinded Prospective Observational Study.

Objective: To determine the percentage of drug remaining in discarded antibiotic vials after use.Design: Blinded prospective observational trial.Setting: 26-bed Australian metropolitan tertiary referral intensive care unit.Main outcome measures: Percentage of labelled dose remaining in the vial after discard.Method: Discarded antibiotic vials collected over a 7-day period in an adult intensive care unit were analysed. Each collected vial had any drug remnant washed out and made up to a known volume. A 1 ml aliquot of each vials washings was analysed using high performance liquid chromatography. From this concentration, the percentage of the drug remaining in the vial after discard was calculated. Additionally, each vial was weighed before and after washing to determine the weight of the remnant in each vial.Results: A total of 311 vials comprising of 11 different drugs and 14 individual vial types were collected. The median residual drug error across all vials was 3.7 %. The drug with the highest median was piperacillin at 6.1 % (IQR 4.3) and the lowest was amoxicillin 0.2 % (IQR 0.1). The single highest value for a given vial was vancomycin (500 mg) with 33.2 % and the lowest for a given vial was 0.1 % amoxicillin (1 g). These two drugs also exhibited the greatest range between the maximum and minimum value for any drug being 32 % and 0.9 % respectively.Conclusions: Our study shows that up to a third of the intended dose may fail to reach the patient, highlighting a significant factor in the administration of antibiotics to the critically ill population. Implications for clinical practice: Residual drug often remains in antibiotic vials meaning that drug is not reaching the patient. There is considerable variation in the method by which medications are reconstituted in clinical settings. Two person checks should be completed after reconstitution in order to ensure that the medication is fully reconstituted and extracted from the vial.