Blood collection techniques, heparin and quinidine protein binding

Area of Science:

• Pharmacokinetics
• Clinical Chemistry
• Analytical Toxicology

Background:

• Accurate measurement of unbound quinidine is crucial for therapeutic drug monitoring and understanding its pharmacodynamics.
• Previous methods for assessing quinidine binding may be subject to pre-analytical variables affecting results.

Purpose of the Study:

• To evaluate the impact of blood collection methods and heparin on the accuracy of unbound quinidine fraction measurements.
• To establish optimal conditions for reliable in vitro determination of quinidine binding.

Main Methods:

• Blood samples were collected using all-glass syringes and Vacutainers (containing rubber stoppers).
• Unbound quinidine was quantified using ultrafiltration and a double-extraction assay after quinidine sulfate addition.
• The effect of varying heparin concentrations (in vitro and in vivo) on quinidine binding was assessed.

Main Results:

• Vacutainer collection led to erroneous and variable decreases in quinidine binding due to rubber-stopper interaction.
• Normal unbound quinidine fraction was 10% in healthy volunteers, with variations in heart failure and renal failure patients.
• Cardiac catheterization patients exhibited significantly elevated unbound quinidine (24%), coinciding with in vivo heparin administration.

Conclusions:

• All-glass or equivalent equipment is essential for accurate measurement of unbound quinidine fractions.
• Heparin significantly influences quinidine binding, necessitating careful handling of samples from patients receiving heparin.
• Standardized blood collection and analysis protocols are critical for reliable quinidine therapeutic drug monitoring.