Background
DBS are well established for testing several different drug levels. DBS for penicillin has been developed to assist with pharmacokinetic studies in children, however the stability of DBS has not been validated. DBS, like other methods still require freezing for long term storage.
Aims
To assess the reliability of DBS as an alternative for collecting blood penicillin levels in real world scenarios.
Methods
Fresh heparinsed blood was collected and spiked with penicillin (1mg/L) and dispensed on to standard protein saver cards (40µL/spot). All samples were then placed in an air tight container with desiccant. Samples were exposed to a range of temperatures to mimic real collection scenarios and degradation was assessed; refrigeration (4°C), room temperature (22°C), hot room (35°C), and hot car (45°C). An esky (with ice bricks) and portable fridge (Waeco) sampling was also conducted with exposure to 45°C ambient temperature.
Results
At 4°C and the portable fridge (10°C), there was no significant penicillin degradation at 8 hours. Room temperature showed minimal degradation (1.5%) at 8 hours. Esky with ice-bricks expose to 45°C for 8 hours showed a 2.5% degradation of penicillin. When dried in hot environments DBS showed accelerated degradation of penicillin (>5%) at 2.5hours (35°C) and less than 1 hour (45°C).
Conclusion
When using DBS to assess penicillin levels, keeping temperatures <22°C or <10°C allow approximately 6 hours and 8 hours of sample stability respectively. These results validate the use of the DBS penicillin assay as a viable alternative to traditional collection methods in clinical practice.