Standard Procedure for PK Sample Collection from Peripheral IV Line
When collecting PK samples from a peripheral IV line used for saline flushing only (not continuous infusion), you must discard an adequate volume of blood before collecting the actual sample to prevent dilution from residual flush solution.
Core Sampling Protocol
Pre-Collection Requirements
Record precise timing: Document the exact time of oral drug administration and each sample collection using calendar time (month, day, hours, minutes) to ensure accurate PK modeling 1, 2
Obtain baseline sample: Collect a pre-dose sample (time 0) before drug administration to establish baseline levels 1, 2
Document recent dosing history: Record the times and doses of any recent prior doses of the same medication 1
Critical IV Line Sampling Technique
The key procedural step when sampling from a peripheral IV line that is flushed with saline:
Discard volume first: Before collecting each PK sample, withdraw and discard 3-5 mL of blood (or at least 2-3 times the dead space volume of the catheter and extension tubing) to clear any residual saline flush that could dilute your sample
Then collect the actual sample: After discarding the initial volume, collect your PK sample in the appropriate tube
Flush after collection: After obtaining the sample, flush the line again with saline to maintain patency for the next timepoint
Sample Collection Timepoints
Your specified timepoints (0,30,60,120,180 minutes) are appropriate for capturing early absorption and distribution phases of an oral drug 1
Record actual collection times: Document the precise time each sample is actually collected, not just the scheduled time, as delays can significantly affect PK analysis 1, 2
Laboratory Handling
Use appropriate assay methods: Ensure the laboratory uses validated analytical methods suitable for your specific drug 1
Report all measurements: Include any values below the limit of quantification (BLQ) rather than discarding them, as this data is valuable for PK modeling 1, 3
Standardize units: Report concentrations in consistent units (e.g., ng/mL or μg/mL) 1
Common Pitfalls to Avoid
Inadequate discard volume: Failing to discard sufficient blood before sample collection is the most critical error when using an IV line for PK sampling, as residual saline will falsely lower measured drug concentrations
Imprecise timing documentation: Recording only approximate times rather than exact times compromises the accuracy of PK parameter estimation 1, 2
Sampling from the same line used for drug infusion: While not applicable to your oral drug scenario, never sample from a line used to administer IV medication without adequate discard volume and time separation
Discarding BLQ values: Laboratories may report concentrations as "undetectable" or "<LLOQ" - these should be recorded as reported, not excluded from analysis 1, 3