Background Pharmacokinetic monitoring optimises drug treatment. However, blood samples should be carefully collected at the right time after drug administration. Otherwise, drug levels could be interpreted in the wrong way and the physician could make an incorrect clinical decision.

Purpose To evaluate the percentage of blood samples collected at the wrong times in the Emergency Department (ED) with respect to time after drug administration.

Material and methods A prospective observational study was conducted in the ED. All patients who took medicines that should be monitored were included. The study period was 20 days (June 2014). The following variables were recorded: demographics (age and gender) and pharmacokinetics (drug name, time of drug administration, time of sample collection and number of drug levels requested per patient). The collection times recommended in our institution are: a) digoxin: at least 8 h after oral administration and 3 h after intravenous administration; b) paracetamol poisoning: at least 4 h after the last administration; c) valproate, phenobarbital, carbamazepine and lithium: prior to next dose (trough level).

Results A total of 40 patients fulfilled the inclusion criteria. 17 patients had plasma drug concentration measurements (65% were female and the median age was 65). The total number of drug measurements was 40 (1–5 measurements per patient). Regarding wrong sampling times, 20% blood samples (8/40) were collected at the wrong times: a) digoxin: 5/17 measurements (29%); b) paracetamol: 2/11 (18%), c) valproate: 1/6 (17%), d) phenobarbital: 0/3 (0%); e) carbamazepine: 0/1 (0%); f) lithium: 0/2 (0%).

Conclusion A high percentage of drug levels were collected at the wrong times in the ED. This fact could lead to unnecessary sampling and data misinterpretation. For this reason, pharmacokinetics training provided by clinical pharmacists prior to blood sampling should be mandatory.

References and/or acknowledgements No conflict of interest.